Merge branch 'vb_arc_welder' into master_262

lib/Slic3r/Geometry.pm

@@ -15,7 +15,6 @@ our @EXPORT_OK = qw(
 
     X Y Z
     convex_hull
-    chained_path_from
     deg2rad
     rad2deg
 );

src/libslic3r/AABBTreeLines.hpp

@@ -345,7 +345,7 @@ public:
         return dist;
     }
 
-    std::vector<size_t> all_lines_in_radius(const Vec<2, Scalar> &point, Floating radius)
+    std::vector<size_t> all_lines_in_radius(const Vec<2, Scalar> &point, Floating radius) const
     {
         return AABBTreeLines::all_lines_in_radius(this->lines, this->tree, point.template cast<Floating>(), radius * radius);
     }

src/libslic3r/Brim.cpp

@@ -490,8 +490,10 @@ static void make_inner_brim(const Print                   &print,
 
     loops = union_pt_chained_outside_in(loops);
     std::reverse(loops.begin(), loops.end());
-    extrusion_entities_append_loops(brim.entities, std::move(loops), ExtrusionRole::Skirt, float(flow.mm3_per_mm()),
-                                    float(flow.width()), float(print.skirt_first_layer_height()));
+    extrusion_entities_append_loops(brim.entities, std::move(loops), 
+        ExtrusionAttributes{
+            ExtrusionRole::Skirt,
+            ExtrusionFlow{ float(flow.mm3_per_mm()), float(flow.width()), float(print.skirt_first_layer_height()) } });
 }
 
 // Produce brim lines around those objects, that have the brim enabled.
@@ -672,7 +674,9 @@ ExtrusionEntityCollection make_brim(const Print &print, PrintTryCancel try_cance
 				if (i + 1 == j && first_path.size() > 3 && first_path.front().x() == first_path.back().x() && first_path.front().y() == first_path.back().y()) {
 					auto *loop = new ExtrusionLoop();
                     brim.entities.emplace_back(loop);
-					loop->paths.emplace_back(ExtrusionRole::Skirt, float(flow.mm3_per_mm()), float(flow.width()), float(print.skirt_first_layer_height()));
+                    loop->paths.emplace_back(ExtrusionAttributes{
+                        ExtrusionRole::Skirt, 
+                        ExtrusionFlow{ float(flow.mm3_per_mm()), float(flow.width()), float(print.skirt_first_layer_height()) } });
 		            Points &points = loop->paths.front().polyline.points;
 		            points.reserve(first_path.size());
 		            for (const ClipperLib_Z::IntPoint &pt : first_path)
@@ -683,7 +687,9 @@ ExtrusionEntityCollection make_brim(const Print &print, PrintTryCancel try_cance
 			    	ExtrusionEntityCollection this_loop_trimmed;
 					this_loop_trimmed.entities.reserve(j - i);
 			    	for (; i < j; ++ i) {
-			            this_loop_trimmed.entities.emplace_back(new ExtrusionPath(ExtrusionRole::Skirt, float(flow.mm3_per_mm()), float(flow.width()), float(print.skirt_first_layer_height())));
+                        this_loop_trimmed.entities.emplace_back(new ExtrusionPath({
+                            ExtrusionRole::Skirt,
+                            ExtrusionFlow{ float(flow.mm3_per_mm()), float(flow.width()), float(print.skirt_first_layer_height()) } }));
 						const ClipperLib_Z::Path &path = *loops_trimmed_order[i].first;
 			            Points &points = dynamic_cast<ExtrusionPath*>(this_loop_trimmed.entities.back())->polyline.points;
 			            points.reserve(path.size());
@@ -699,7 +705,9 @@ ExtrusionEntityCollection make_brim(const Print &print, PrintTryCancel try_cance
 			}
 		}
     } else {
-        extrusion_entities_append_loops_and_paths(brim.entities, std::move(all_loops), ExtrusionRole::Skirt, float(flow.mm3_per_mm()), float(flow.width()), float(print.skirt_first_layer_height()));
+        extrusion_entities_append_loops_and_paths(brim.entities, std::move(all_loops), 
+            ExtrusionAttributes{ ExtrusionRole::Skirt,
+                ExtrusionFlow{ float(flow.mm3_per_mm()), float(flow.width()), float(print.skirt_first_layer_height()) } });
     }
 
     make_inner_brim(print, top_level_objects_with_brim, bottom_layers_expolygons, brim);

src/libslic3r/CMakeLists.txt

@@ -142,8 +142,12 @@ set(SLIC3R_SOURCES
     GCode/ConflictChecker.hpp
     GCode/CoolingBuffer.cpp
     GCode/CoolingBuffer.hpp
+    GCode/ExtrusionProcessor.cpp
+    GCode/ExtrusionProcessor.hpp
     GCode/FindReplace.cpp
     GCode/FindReplace.hpp
+    GCode/GCodeWriter.cpp
+    GCode/GCodeWriter.hpp
     GCode/PostProcessor.cpp
     GCode/PostProcessor.hpp
     GCode/PressureEqualizer.cpp
@@ -156,10 +160,16 @@ set(SLIC3R_SOURCES
     GCode/SpiralVase.hpp
     GCode/SeamPlacer.cpp
     GCode/SeamPlacer.hpp
+    GCode/SmoothPath.cpp
+    GCode/SmoothPath.hpp
     GCode/ToolOrdering.cpp
     GCode/ToolOrdering.hpp
+    GCode/Wipe.cpp
+    GCode/Wipe.hpp
     GCode/WipeTower.cpp
     GCode/WipeTower.hpp
+    GCode/WipeTowerIntegration.cpp
+    GCode/WipeTowerIntegration.hpp
     GCode/GCodeProcessor.cpp
     GCode/GCodeProcessor.hpp
     GCode/AvoidCrossingPerimeters.cpp
@@ -170,10 +180,10 @@ set(SLIC3R_SOURCES
     GCodeReader.hpp
     # GCodeSender.cpp
     # GCodeSender.hpp
-    GCodeWriter.cpp
-    GCodeWriter.hpp
     Geometry.cpp
     Geometry.hpp
+    Geometry/ArcWelder.cpp
+    Geometry/ArcWelder.hpp
     Geometry/Bicubic.hpp
     Geometry/Circle.cpp
     Geometry/Circle.hpp

src/libslic3r/CustomGCode.cpp

@@ -1,7 +1,7 @@
 #include "CustomGCode.hpp"
 #include "Config.hpp"
 #include "GCode.hpp"
-#include "GCodeWriter.hpp"
+#include "GCode/GCodeWriter.hpp"
 
 namespace Slic3r {
 

src/libslic3r/Extruder.cpp

@@ -1,5 +1,5 @@
 #include "Extruder.hpp"
-#include "GCodeWriter.hpp"
+#include "GCode/GCodeWriter.hpp"
 #include "PrintConfig.hpp"
 
 namespace Slic3r {

src/libslic3r/ExtrusionEntity.cpp

@@ -2,6 +2,7 @@
 #include "ExtrusionEntityCollection.hpp"
 #include "ExPolygon.hpp"
 #include "ClipperUtils.hpp"
+#include "Exception.hpp"
 #include "Extruder.hpp"
 #include "Flow.hpp"
 #include <cmath>
@@ -38,12 +39,12 @@ double ExtrusionPath::length() const
 void ExtrusionPath::_inflate_collection(const Polylines &polylines, ExtrusionEntityCollection* collection) const
 {
     for (const Polyline &polyline : polylines)
-        collection->entities.emplace_back(new ExtrusionPath(polyline, *this));
+        collection->entities.emplace_back(new ExtrusionPath(polyline, this->attributes()));
 }
 
 void ExtrusionPath::polygons_covered_by_width(Polygons &out, const float scaled_epsilon) const
 {
-    polygons_append(out, offset(this->polyline, float(scale_(this->width/2)) + scaled_epsilon));
+    polygons_append(out, offset(this->polyline, float(scale_(m_attributes.width/2)) + scaled_epsilon));
 }
 
 void ExtrusionPath::polygons_covered_by_spacing(Polygons &out, const float scaled_epsilon) const
@@ -51,8 +52,8 @@ void ExtrusionPath::polygons_covered_by_spacing(Polygons &out, const float scale
     // Instantiating the Flow class to get the line spacing.
     // Don't know the nozzle diameter, setting to zero. It shall not matter it shall be optimized out by the compiler.
     bool bridge = this->role().is_bridge();
-    assert(! bridge || this->width == this->height);
-    auto flow = bridge ? Flow::bridging_flow(this->width, 0.f) : Flow(this->width, this->height, 0.f);
+    assert(! bridge || m_attributes.width == m_attributes.height);
+    auto flow = bridge ? Flow::bridging_flow(m_attributes.width, 0.f) : Flow(m_attributes.width, m_attributes.height, 0.f);
     polygons_append(out, offset(this->polyline, 0.5f * float(flow.scaled_spacing()) + scaled_epsilon));
 }
 
@@ -87,7 +88,7 @@ double ExtrusionMultiPath::min_mm3_per_mm() const
 {
     double min_mm3_per_mm = std::numeric_limits<double>::max();
     for (const ExtrusionPath &path : this->paths)
-        min_mm3_per_mm = std::min(min_mm3_per_mm, path.mm3_per_mm);
+        min_mm3_per_mm = std::min(min_mm3_per_mm, path.min_mm3_per_mm());
     return min_mm3_per_mm;
 }
 
@@ -112,21 +113,34 @@ Polyline ExtrusionMultiPath::as_polyline() const
     return out;
 }
 
-bool ExtrusionLoop::make_clockwise()
+double ExtrusionLoop::area() const
 {
-    bool was_ccw = this->polygon().is_counter_clockwise();
-    if (was_ccw) this->reverse();
-    return was_ccw;
-}
-
-bool ExtrusionLoop::make_counter_clockwise()
-{
-    bool was_cw = this->polygon().is_clockwise();
-    if (was_cw) this->reverse();
-    return was_cw;
+    double a = 0;
+    for (const ExtrusionPath &path : this->paths) {
+        assert(path.size() >= 2);
+        if (path.size() >= 2) {
+            // Assumming that the last point of one path segment is repeated at the start of the following path segment.
+            auto it = path.polyline.points.begin();
+            Point prev = *it ++;
+            for (; it != path.polyline.points.end(); ++ it) {
+                a += cross2(prev.cast<double>(), it->cast<double>());
+                prev = *it;
+            }
+        }
+    }
+    return a * 0.5;
 }
 
 void ExtrusionLoop::reverse()
+{
+#if 0
+    this->reverse_loop();
+#else
+    throw Slic3r::LogicError("ExtrusionLoop::reverse() must NOT be called");
+#endif
+}
+
+void ExtrusionLoop::reverse_loop()
 {
     for (ExtrusionPath &path : this->paths)
         path.reverse();
@@ -248,8 +262,8 @@ void ExtrusionLoop::split_at(const Point &point, bool prefer_non_overhang, const
     
     // now split path_idx in two parts
     const ExtrusionPath &path = this->paths[path_idx];
-    ExtrusionPath p1(path.role(), path.mm3_per_mm, path.width, path.height);
-    ExtrusionPath p2(path.role(), path.mm3_per_mm, path.width, path.height);
+    ExtrusionPath p1(path.attributes());
+    ExtrusionPath p2(path.attributes());
     path.polyline.split_at(p, &p1.polyline, &p2.polyline);
     
     if (this->paths.size() == 1) {
@@ -316,7 +330,7 @@ double ExtrusionLoop::min_mm3_per_mm() const
 {
     double min_mm3_per_mm = std::numeric_limits<double>::max();
     for (const ExtrusionPath &path : this->paths)
-        min_mm3_per_mm = std::min(min_mm3_per_mm, path.mm3_per_mm);
+        min_mm3_per_mm = std::min(min_mm3_per_mm, path.min_mm3_per_mm());
     return min_mm3_per_mm;
 }
 

src/libslic3r/ExtrusionEntity.hpp

@@ -3,10 +3,12 @@
 
 #include "libslic3r.h"
 #include "ExtrusionRole.hpp"
+#include "Flow.hpp"
 #include "Polygon.hpp"
 #include "Polyline.hpp"
 
 #include <assert.h>
+#include <optional>
 #include <string_view>
 #include <numeric>
 
@@ -55,28 +57,91 @@ public:
     virtual double total_volume() const = 0;
 };
 
-typedef std::vector<ExtrusionEntity*> ExtrusionEntitiesPtr;
+using ExtrusionEntitiesPtr = std::vector<ExtrusionEntity*>;
+
+// Const reference for ordering extrusion entities without having to modify them.
+class ExtrusionEntityReference final
+{
+public:
+    ExtrusionEntityReference() = delete;
+    ExtrusionEntityReference(const ExtrusionEntity &extrusion_entity, bool flipped) : 
+        m_extrusion_entity(&extrusion_entity), m_flipped(flipped) {}
+    ExtrusionEntityReference operator=(const ExtrusionEntityReference &rhs) 
+        { m_extrusion_entity = rhs.m_extrusion_entity; m_flipped = rhs.m_flipped; return *this; }
+
+    const ExtrusionEntity& extrusion_entity() const { return *m_extrusion_entity; }
+    template<typename Type>
+    const Type*            cast()             const { return dynamic_cast<const Type*>(m_extrusion_entity); }
+    bool                   flipped()          const { return m_flipped; }
+
+private:
+    const ExtrusionEntity *m_extrusion_entity;
+    bool                   m_flipped;
+};
+
+using ExtrusionEntityReferences = std::vector<ExtrusionEntityReference>;
+
+struct ExtrusionFlow
+{
+    ExtrusionFlow() = default;
+    ExtrusionFlow(double mm3_per_mm, float width, float height) : 
+        mm3_per_mm{ mm3_per_mm }, width{ width }, height{ height } {}
+    ExtrusionFlow(const Flow &flow) :
+        mm3_per_mm(flow.mm3_per_mm()), width(flow.width()), height(flow.height()) {}
+
+    // Volumetric velocity. mm^3 of plastic per mm of linear head motion. Used by the G-code generator.
+    double          mm3_per_mm{ -1. };
+    // Width of the extrusion, used for visualization purposes.
+    float           width{ -1.f };
+    // Height of the extrusion, used for visualization purposes.
+    float           height{ -1.f };
+};
+
+inline bool operator==(const ExtrusionFlow &lhs, const ExtrusionFlow &rhs)
+{
+    return lhs.mm3_per_mm == rhs.mm3_per_mm && lhs.width == rhs.width && lhs.height == rhs.height;
+}
+
+struct OverhangAttributes {
+    float start_distance_from_prev_layer;
+    float end_distance_from_prev_layer;
+    float proximity_to_curled_lines; //value between 0 and 1
+};
+
+struct ExtrusionAttributes : ExtrusionFlow
+{
+    ExtrusionAttributes() = default;
+    ExtrusionAttributes(ExtrusionRole role) : role{ role } {}
+    ExtrusionAttributes(ExtrusionRole role, const Flow &flow) : role{ role }, ExtrusionFlow{ flow } {}
+    ExtrusionAttributes(ExtrusionRole role, const ExtrusionFlow &flow) : role{ role }, ExtrusionFlow{ flow } {}
+
+    // What is the role / purpose of this extrusion?
+    ExtrusionRole   role{ ExtrusionRole::None };
+    // OVerhangAttributes are currently computed for perimeters if dynamic overhangs are enabled. 
+    // They are used to control fan and print speed in export.
+    std::optional<OverhangAttributes> overhang_attributes;
+};
+
+inline bool operator==(const ExtrusionAttributes &lhs, const ExtrusionAttributes &rhs)
+{
+    return static_cast<const ExtrusionFlow&>(lhs) == static_cast<const ExtrusionFlow&>(rhs) &&
+           lhs.role == rhs.role;
+}
 
 class ExtrusionPath : public ExtrusionEntity
 {
 public:
     Polyline polyline;
-    // Volumetric velocity. mm^3 of plastic per mm of linear head motion. Used by the G-code generator.
-    double mm3_per_mm;
-    // Width of the extrusion, used for visualization purposes.
-    float width;
-    // Height of the extrusion, used for visualization purposes.
-    float height;
 
-    ExtrusionPath(ExtrusionRole role) : mm3_per_mm(-1), width(-1), height(-1), m_role(role) {}
-    ExtrusionPath(ExtrusionRole role, double mm3_per_mm, float width, float height) : mm3_per_mm(mm3_per_mm), width(width), height(height), m_role(role) {}
-    ExtrusionPath(const ExtrusionPath& rhs) : polyline(rhs.polyline), mm3_per_mm(rhs.mm3_per_mm), width(rhs.width), height(rhs.height), m_role(rhs.m_role) {}
-    ExtrusionPath(ExtrusionPath&& rhs) : polyline(std::move(rhs.polyline)), mm3_per_mm(rhs.mm3_per_mm), width(rhs.width), height(rhs.height), m_role(rhs.m_role) {}
-    ExtrusionPath(const Polyline &polyline, const ExtrusionPath &rhs) : polyline(polyline), mm3_per_mm(rhs.mm3_per_mm), width(rhs.width), height(rhs.height), m_role(rhs.m_role) {}
-    ExtrusionPath(Polyline &&polyline, const ExtrusionPath &rhs) : polyline(std::move(polyline)), mm3_per_mm(rhs.mm3_per_mm), width(rhs.width), height(rhs.height), m_role(rhs.m_role) {}
+    ExtrusionPath(ExtrusionRole role) : m_attributes{ role } {}
+    ExtrusionPath(const ExtrusionAttributes &attributes) : m_attributes(attributes) {}
+    ExtrusionPath(const ExtrusionPath &rhs) : polyline(rhs.polyline), m_attributes(rhs.m_attributes) {}
+    ExtrusionPath(ExtrusionPath &&rhs) : polyline(std::move(rhs.polyline)), m_attributes(rhs.m_attributes) {}
+    ExtrusionPath(const Polyline &polyline, const ExtrusionAttributes &attribs) : polyline(polyline), m_attributes(attribs) {}
+    ExtrusionPath(Polyline &&polyline, const ExtrusionAttributes &attribs) : polyline(std::move(polyline)), m_attributes(attribs) {}
 
-    ExtrusionPath& operator=(const ExtrusionPath& rhs) { m_role = rhs.m_role; this->mm3_per_mm = rhs.mm3_per_mm; this->width = rhs.width; this->height = rhs.height; this->polyline = rhs.polyline; return *this; }
-    ExtrusionPath& operator=(ExtrusionPath&& rhs) { m_role = rhs.m_role; this->mm3_per_mm = rhs.mm3_per_mm; this->width = rhs.width; this->height = rhs.height; this->polyline = std::move(rhs.polyline); return *this; }
+    ExtrusionPath& operator=(const ExtrusionPath &rhs) { this->polyline = rhs.polyline; m_attributes = rhs.m_attributes; return *this; }
+    ExtrusionPath& operator=(ExtrusionPath &&rhs) { this->polyline = std::move(rhs.polyline); m_attributes = rhs.m_attributes; return *this; }
 
 	ExtrusionEntity* clone() const override { return new ExtrusionPath(*this); }
     // Create a new object, initialize it with this object using the move semantics.
@@ -97,7 +162,16 @@ public:
     void clip_end(double distance);
     void simplify(double tolerance);
     double length() const override;
-    ExtrusionRole role() const override { return m_role; }
+   
+    const ExtrusionAttributes&  attributes() const { return m_attributes; }
+    ExtrusionRole               role() const override { return m_attributes.role; }
+    float                       width() const { return m_attributes.width; }
+    float                       height() const { return m_attributes.height; }
+    double                      mm3_per_mm() const { return m_attributes.mm3_per_mm; }
+    // Minimum volumetric velocity of this extrusion entity. Used by the constant nozzle pressure algorithm.
+    double                      min_mm3_per_mm() const override { return m_attributes.mm3_per_mm; }
+    std::optional<OverhangAttributes>& overhang_attributes_mutable() { return m_attributes.overhang_attributes; }
+
     // Produce a list of 2D polygons covered by the extruded paths, offsetted by the extrusion width.
     // Increase the offset by scaled_epsilon to achieve an overlap, so a union will produce no gaps.
     void        polygons_covered_by_width(Polygons &out, const float scaled_epsilon) const override;
@@ -109,23 +183,25 @@ public:
         { Polygons out; this->polygons_covered_by_width(out, scaled_epsilon); return out; }
     Polygons    polygons_covered_by_spacing(const float scaled_epsilon = 0.f) const
         { Polygons out; this->polygons_covered_by_spacing(out, scaled_epsilon); return out; }
-    // Minimum volumetric velocity of this extrusion entity. Used by the constant nozzle pressure algorithm.
-    double min_mm3_per_mm() const override { return this->mm3_per_mm; }
+
     Polyline    as_polyline() const override { return this->polyline; }
     void        collect_polylines(Polylines &dst) const override { if (! this->polyline.empty()) dst.emplace_back(this->polyline); }
     void        collect_points(Points &dst) const override { append(dst, this->polyline.points); }
-    double total_volume() const override { return mm3_per_mm * unscale<double>(length()); }
+    double      total_volume() const override { return m_attributes.mm3_per_mm * unscale<double>(length()); }
 
 private:
     void        _inflate_collection(const Polylines &polylines, ExtrusionEntityCollection* collection) const;
 
-    ExtrusionRole m_role;
+    ExtrusionAttributes     m_attributes;
 };
 
 class ExtrusionPathOriented : public ExtrusionPath
 {
 public:
-    ExtrusionPathOriented(ExtrusionRole role, double mm3_per_mm, float width, float height) : ExtrusionPath(role, mm3_per_mm, width, height) {}
+    ExtrusionPathOriented(const ExtrusionAttributes &attribs) : ExtrusionPath(attribs) {}
+    ExtrusionPathOriented(const Polyline &polyline, const ExtrusionAttributes &attribs) : ExtrusionPath(polyline, attribs) {}
+    ExtrusionPathOriented(Polyline &&polyline, const ExtrusionAttributes &attribs) : ExtrusionPath(std::move(polyline), attribs) {}
+
     ExtrusionEntity* clone() const override { return new ExtrusionPathOriented(*this); }
     // Create a new object, initialize it with this object using the move semantics.
     ExtrusionEntity* clone_move() override { return new ExtrusionPathOriented(std::move(*this)); }
@@ -192,7 +268,8 @@ class ExtrusionLoop : public ExtrusionEntity
 public:
     ExtrusionPaths paths;
     
-    ExtrusionLoop(ExtrusionLoopRole role = elrDefault) : m_loop_role(role) {}
+    ExtrusionLoop() = default;
+    ExtrusionLoop(ExtrusionLoopRole role) : m_loop_role(role) {}
     ExtrusionLoop(const ExtrusionPaths &paths, ExtrusionLoopRole role = elrDefault) : paths(paths), m_loop_role(role) {}
     ExtrusionLoop(ExtrusionPaths &&paths, ExtrusionLoopRole role = elrDefault) : paths(std::move(paths)), m_loop_role(role) {}
     ExtrusionLoop(const ExtrusionPath &path, ExtrusionLoopRole role = elrDefault) : m_loop_role(role) 
@@ -204,9 +281,14 @@ public:
 	ExtrusionEntity* clone() const override{ return new ExtrusionLoop (*this); }
     // Create a new object, initialize it with this object using the move semantics.
 	ExtrusionEntity* clone_move() override { return new ExtrusionLoop(std::move(*this)); }
-    bool make_clockwise();
-    bool make_counter_clockwise();
+    double          area() const;
+    bool            is_counter_clockwise() const { return this->area() > 0; }
+    bool            is_clockwise() const { return this->area() < 0; }
+    // Reverse shall never be called on ExtrusionLoop using a virtual function call, it is most likely never what one wants,
+    // as this->can_reverse() returns false for an ExtrusionLoop.
     void            reverse() override;
+    // Used by PerimeterGenerator to reorient extrusion loops.
+    void            reverse_loop();
     const Point&    first_point() const override { return this->paths.front().polyline.points.front(); }
     const Point&    last_point() const override { assert(this->first_point() == this->paths.back().polyline.points.back()); return this->first_point(); }
     const Point&    middle_point() const override { auto& path = this->paths[this->paths.size() / 2]; return path.polyline.points[path.polyline.size() / 2]; }
@@ -259,59 +341,51 @@ public:
 #endif /* NDEBUG */
 
 private:
-    ExtrusionLoopRole m_loop_role;
+    ExtrusionLoopRole m_loop_role{ elrDefault };
 };
 
-inline void extrusion_paths_append(ExtrusionPaths &dst, Polylines &polylines, ExtrusionRole role, double mm3_per_mm, float width, float height)
+inline void extrusion_paths_append(ExtrusionPaths &dst, Polylines &polylines, const ExtrusionAttributes &attributes)
 {
     dst.reserve(dst.size() + polylines.size());
     for (Polyline &polyline : polylines)
-        if (polyline.is_valid()) {
-            dst.push_back(ExtrusionPath(role, mm3_per_mm, width, height));
-            dst.back().polyline = polyline;
-        }
+        if (polyline.is_valid())
+            dst.emplace_back(polyline, attributes);
 }
 
-inline void extrusion_paths_append(ExtrusionPaths &dst, Polylines &&polylines, ExtrusionRole role, double mm3_per_mm, float width, float height)
+inline void extrusion_paths_append(ExtrusionPaths &dst, Polylines &&polylines, const ExtrusionAttributes &attributes)
 {
     dst.reserve(dst.size() + polylines.size());
     for (Polyline &polyline : polylines)
-        if (polyline.is_valid()) {
-            dst.push_back(ExtrusionPath(role, mm3_per_mm, width, height));
-            dst.back().polyline = std::move(polyline);
-        }
+        if (polyline.is_valid())
+            dst.emplace_back(std::move(polyline), attributes);
     polylines.clear();
 }
 
-inline void extrusion_entities_append_paths(ExtrusionEntitiesPtr &dst, const Polylines &polylines, ExtrusionRole role, double mm3_per_mm, float width, float height, bool can_reverse = true)
+inline void extrusion_entities_append_paths(ExtrusionEntitiesPtr &dst, const Polylines &polylines, const ExtrusionAttributes &attributes, bool can_reverse = true)
 {
     dst.reserve(dst.size() + polylines.size());
     for (const Polyline &polyline : polylines)
-        if (polyline.is_valid()) {
-            ExtrusionPath* extrusion_path = can_reverse ? new ExtrusionPath(role, mm3_per_mm, width, height) : new ExtrusionPathOriented(role, mm3_per_mm, width, height);
-            dst.push_back(extrusion_path);
-            extrusion_path->polyline = polyline;
-        }
+        if (polyline.is_valid())
+            dst.emplace_back(can_reverse ? new ExtrusionPath(polyline, attributes) : new ExtrusionPathOriented(polyline, attributes));
 }
 
-inline void extrusion_entities_append_paths(ExtrusionEntitiesPtr &dst, Polylines &&polylines, ExtrusionRole role, double mm3_per_mm, float width, float height, bool can_reverse = true)
+inline void extrusion_entities_append_paths(ExtrusionEntitiesPtr &dst, Polylines &&polylines, const ExtrusionAttributes &attributes, bool can_reverse = true)
 {
     dst.reserve(dst.size() + polylines.size());
     for (Polyline &polyline : polylines)
-        if (polyline.is_valid()) {
-            ExtrusionPath *extrusion_path = can_reverse ? new ExtrusionPath(role, mm3_per_mm, width, height) : new ExtrusionPathOriented(role, mm3_per_mm, width, height);
-            dst.push_back(extrusion_path);
-            extrusion_path->polyline = std::move(polyline);
-        }
+        if (polyline.is_valid())
+            dst.emplace_back(can_reverse ?
+                new ExtrusionPath(std::move(polyline), attributes) :
+                new ExtrusionPathOriented(std::move(polyline), attributes));
     polylines.clear();
 }
 
-inline void extrusion_entities_append_loops(ExtrusionEntitiesPtr &dst, Polygons &&loops, ExtrusionRole role, double mm3_per_mm, float width, float height)
+inline void extrusion_entities_append_loops(ExtrusionEntitiesPtr &dst, Polygons &&loops, const ExtrusionAttributes &attributes)
 {
     dst.reserve(dst.size() + loops.size());
     for (Polygon &poly : loops) {
         if (poly.is_valid()) {
-            ExtrusionPath path(role, mm3_per_mm, width, height);
+            ExtrusionPath path(attributes);
             path.polyline.points = std::move(poly.points);
             path.polyline.points.push_back(path.polyline.points.front());
             dst.emplace_back(new ExtrusionLoop(std::move(path)));
@@ -320,22 +394,14 @@ inline void extrusion_entities_append_loops(ExtrusionEntitiesPtr &dst, Polygons
     loops.clear();
 }
 
-inline void extrusion_entities_append_loops_and_paths(ExtrusionEntitiesPtr &dst, Polylines &&polylines, ExtrusionRole role, double mm3_per_mm, float width, float height)
+inline void extrusion_entities_append_loops_and_paths(ExtrusionEntitiesPtr &dst, Polylines &&polylines, const ExtrusionAttributes &attributes)
 {
     dst.reserve(dst.size() + polylines.size());
-    for (Polyline &polyline : polylines) {
-        if (polyline.is_valid()) {
-            if (polyline.is_closed()) {
-                ExtrusionPath extrusion_path(role, mm3_per_mm, width, height);
-                extrusion_path.polyline = std::move(polyline);
-                dst.emplace_back(new ExtrusionLoop(std::move(extrusion_path)));
-            } else {
-                ExtrusionPath *extrusion_path = new ExtrusionPath(role, mm3_per_mm, width, height);
-                extrusion_path->polyline      = std::move(polyline);
-                dst.emplace_back(extrusion_path);
-            }
-        }
-    }
+    for (Polyline &polyline : polylines)
+        if (polyline.is_valid())
+            dst.emplace_back(polyline.is_closed() ?
+                static_cast<ExtrusionEntity*>(new ExtrusionLoop(ExtrusionPath{ std::move(polyline), attributes })) :
+                static_cast<ExtrusionEntity*>(new ExtrusionPath(std::move(polyline), attributes)));
     polylines.clear();
 }
 

src/libslic3r/ExtrusionEntityCollection.cpp

@@ -6,6 +6,7 @@
 
 namespace Slic3r {
 
+#if 0
 void filter_by_extrusion_role_in_place(ExtrusionEntitiesPtr &extrusion_entities, ExtrusionRole role)
 {
 	if (role != ExtrusionRole::Mixed) {
@@ -17,6 +18,7 @@ void filter_by_extrusion_role_in_place(ExtrusionEntitiesPtr &extrusion_entities,
             last);
 	}
 }
+#endif
 
 ExtrusionEntityCollection::ExtrusionEntityCollection(const ExtrusionPaths &paths)
     : no_sort(false)
@@ -83,18 +85,6 @@ void ExtrusionEntityCollection::remove(size_t i)
     this->entities.erase(this->entities.begin() + i);
 }
 
-ExtrusionEntityCollection ExtrusionEntityCollection::chained_path_from(const ExtrusionEntitiesPtr& extrusion_entities, const Point &start_near, ExtrusionRole role)
-{
-	// Return a filtered copy of the collection.
-    ExtrusionEntityCollection out;
-    out.entities = filter_by_extrusion_role(extrusion_entities, role);
-	// Clone the extrusion entities.
-	for (auto &ptr : out.entities)
-		ptr = ptr->clone();
-	chain_and_reorder_extrusion_entities(out.entities, &start_near);
-    return out;
-}
-
 void ExtrusionEntityCollection::polygons_covered_by_width(Polygons &out, const float scaled_epsilon) const
 {
     for (const ExtrusionEntity *entity : this->entities)

src/libslic3r/ExtrusionEntityCollection.hpp

@@ -7,6 +7,7 @@
 
 namespace Slic3r {
 
+#if 0
 // Remove those items from extrusion_entities, that do not match role.
 // Do nothing if role is mixed.
 // Removed elements are NOT being deleted.
@@ -21,6 +22,7 @@ inline ExtrusionEntitiesPtr filter_by_extrusion_role(const ExtrusionEntitiesPtr
 	filter_by_extrusion_role_in_place(out, role);
 	return out;
 }
+#endif
 
 class ExtrusionEntityCollection : public ExtrusionEntity
 {
@@ -96,9 +98,6 @@ public:
     }
     void replace(size_t i, const ExtrusionEntity &entity);
     void remove(size_t i);
-    static ExtrusionEntityCollection chained_path_from(const ExtrusionEntitiesPtr &extrusion_entities, const Point &start_near, ExtrusionRole role = ExtrusionRole::Mixed);
-    ExtrusionEntityCollection chained_path_from(const Point &start_near, ExtrusionRole role = ExtrusionRole::Mixed) const
-    	{ return this->no_sort ? *this : chained_path_from(this->entities, start_near, role); }
     void reverse() override;
     const Point& first_point() const override { return this->entities.front()->first_point(); }
     const Point& last_point() const override { return this->entities.back()->last_point(); }

src/libslic3r/ExtrusionRole.hpp

@@ -82,6 +82,7 @@ struct ExtrusionRole : public ExtrusionRoleModifiers
     bool is_external_perimeter() const { return this->is_perimeter() && this->is_external(); }
     bool is_infill() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Infill); }
     bool is_solid_infill() const { return this->is_infill() && this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Solid); }
+    bool is_sparse_infill() const { return this->is_infill() && ! this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Solid); }
     bool is_external() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::External); }
     bool is_bridge() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Bridge); }
 
@@ -89,6 +90,9 @@ struct ExtrusionRole : public ExtrusionRoleModifiers
     bool is_support_base() const { return this->is_support() && ! this->is_external(); }
     bool is_support_interface() const { return this->is_support() && this->is_external(); }
     bool is_mixed() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Mixed); }
+
+    // Brim is currently marked as skirt.
+    bool is_skirt() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Skirt); }
 };
 
 // Special flags describing loop

src/libslic3r/ExtrusionSimulator.cpp

@@ -957,9 +957,9 @@ void ExtrusionSimulator::extrude_to_accumulator(const ExtrusionPath &path, const
 	polyline.reserve(path.polyline.points.size());
 	float scalex  = float(viewport.size().x()) / float(bbox.size().x());
 	float scaley  = float(viewport.size().y()) / float(bbox.size().y());
-	float w = scale_(path.width) * scalex;
+	float w = scale_(path.width()) * scalex;
 	//float h = scale_(path.height) * scalex;
-	w = scale_(path.mm3_per_mm / path.height) * scalex;
+	w = scale_(path.mm3_per_mm() / path.height()) * scalex;
 	// printf("scalex: %f, scaley: %f\n", scalex, scaley);
 	// printf("bbox: %d,%d %d,%d\n", bbox.min.x(), bbox.min.y, bbox.max.x(), bbox.max.y);
 	for (Points::const_iterator it = path.polyline.points.begin(); it != path.polyline.points.end(); ++ it) {

src/libslic3r/Fill/Fill.cpp

@@ -558,8 +558,9 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
                 } else {
                     extrusion_entities_append_paths(
                         eec->entities, std::move(polylines),
-                        surface_fill.params.extrusion_role,
-                        flow_mm3_per_mm, float(flow_width), surface_fill.params.flow.height());
+						ExtrusionAttributes{ surface_fill.params.extrusion_role,
+							ExtrusionFlow{ flow_mm3_per_mm, float(flow_width), surface_fill.params.flow.height() } 
+						});
                 }
                 insert_fills_into_islands(*this, uint32_t(surface_fill.region_id), fill_begin, uint32_t(layerm.fills().size()));
 		    }
@@ -904,8 +905,9 @@ void Layer::make_ironing()
 				eec->no_sort = true;
 		        extrusion_entities_append_paths(
 		            eec->entities, std::move(polylines),
-					ExtrusionRole::Ironing,
-		            flow_mm3_per_mm, extrusion_width, float(extrusion_height));
+					ExtrusionAttributes{ ExtrusionRole::Ironing,
+						ExtrusionFlow{ flow_mm3_per_mm, extrusion_width, float(extrusion_height) }
+					});
 				insert_fills_into_islands(*this, ironing_params.region_id, fill_begin, uint32_t(ironing_params.layerm->fills().size()));
 		    }
 		}

src/libslic3r/GCode.hpp

@@ -5,18 +5,22 @@
 #include "JumpPointSearch.hpp"
 #include "libslic3r.h"
 #include "ExPolygon.hpp"
-#include "GCodeWriter.hpp"
 #include "Layer.hpp"
 #include "Point.hpp"
 #include "PlaceholderParser.hpp"
 #include "PrintConfig.hpp"
+#include "Geometry/ArcWelder.hpp"
 #include "GCode/AvoidCrossingPerimeters.hpp"
 #include "GCode/CoolingBuffer.hpp"
 #include "GCode/FindReplace.hpp"
+#include "GCode/GCodeWriter.hpp"
+#include "GCode/PressureEqualizer.hpp"
 #include "GCode/RetractWhenCrossingPerimeters.hpp"
+#include "GCode/SmoothPath.hpp"
 #include "GCode/SpiralVase.hpp"
 #include "GCode/ToolOrdering.hpp"
-#include "GCode/WipeTower.hpp"
+#include "GCode/Wipe.hpp"
+#include "GCode/WipeTowerIntegration.hpp"
 #include "GCode/SeamPlacer.hpp"
 #include "GCode/GCodeProcessor.hpp"
 #include "EdgeGrid.hpp"
@@ -26,12 +30,10 @@
 #include <map>
 #include <string>
 
-#include "GCode/PressureEqualizer.hpp"
-
 namespace Slic3r {
 
 // Forward declarations.
-class GCode;
+class GCodeGenerator;
 
 namespace { struct Item; }
 struct PrintInstance;
@@ -41,71 +43,11 @@ public:
     bool enable;
     
     OozePrevention() : enable(false) {}
-    std::string pre_toolchange(GCode &gcodegen);
-    std::string post_toolchange(GCode &gcodegen);
+    std::string pre_toolchange(GCodeGenerator &gcodegen);
+    std::string post_toolchange(GCodeGenerator &gcodegen);
     
 private:
-    int _get_temp(const GCode &gcodegen) const;
-};
-
-class Wipe {
-public:
-    bool enable;
-    Polyline path;
-    
-    Wipe() : enable(false) {}
-    bool has_path() const { return ! this->path.empty(); }
-    void reset_path() { this->path.clear(); }
-    std::string wipe(GCode &gcodegen, bool toolchange);
-};
-
-class WipeTowerIntegration {
-public:
-    WipeTowerIntegration(
-        const PrintConfig                                           &print_config,
-        const std::vector<WipeTower::ToolChangeResult>              &priming,
-        const std::vector<std::vector<WipeTower::ToolChangeResult>> &tool_changes,
-        const WipeTower::ToolChangeResult                           &final_purge) :
-        m_left(/*float(print_config.wipe_tower_x.value)*/ 0.f),
-        m_right(float(/*print_config.wipe_tower_x.value +*/ print_config.wipe_tower_width.value)),
-        m_wipe_tower_pos(float(print_config.wipe_tower_x.value), float(print_config.wipe_tower_y.value)),
-        m_wipe_tower_rotation(float(print_config.wipe_tower_rotation_angle)),
-        m_extruder_offsets(print_config.extruder_offset.values),
-        m_priming(priming),
-        m_tool_changes(tool_changes),
-        m_final_purge(final_purge),
-        m_layer_idx(-1),
-        m_tool_change_idx(0)
-    {}
-
-    std::string prime(GCode &gcodegen);
-    void next_layer() { ++ m_layer_idx; m_tool_change_idx = 0; }
-    std::string tool_change(GCode &gcodegen, int extruder_id, bool finish_layer);
-    std::string finalize(GCode &gcodegen);
-    std::vector<float> used_filament_length() const;
-
-private:
-    WipeTowerIntegration& operator=(const WipeTowerIntegration&);
-    std::string append_tcr(GCode &gcodegen, const WipeTower::ToolChangeResult &tcr, int new_extruder_id, double z = -1.) const;
-
-    // Postprocesses gcode: rotates and moves G1 extrusions and returns result
-    std::string post_process_wipe_tower_moves(const WipeTower::ToolChangeResult& tcr, const Vec2f& translation, float angle) const;
-
-    // Left / right edges of the wipe tower, for the planning of wipe moves.
-    const float                                                  m_left;
-    const float                                                  m_right;
-    const Vec2f                                                  m_wipe_tower_pos;
-    const float                                                  m_wipe_tower_rotation;
-    const std::vector<Vec2d>                                     m_extruder_offsets;
-
-    // Reference to cached values at the Printer class.
-    const std::vector<WipeTower::ToolChangeResult>              &m_priming;
-    const std::vector<std::vector<WipeTower::ToolChangeResult>> &m_tool_changes;
-    const WipeTower::ToolChangeResult                           &m_final_purge;
-    // Current layer index.
-    int                                                          m_layer_idx;
-    int                                                          m_tool_change_idx;
-    double                                                       m_last_wipe_tower_print_z = 0.f;
+    int _get_temp(const GCodeGenerator &gcodegen) const;
 };
 
 class ColorPrintColors
@@ -129,9 +71,9 @@ struct LayerResult {
     static LayerResult make_nop_layer_result() { return {"", std::numeric_limits<coord_t>::max(), false, false, true}; }
 };
 
-class GCode {
+class GCodeGenerator {
 public:        
-    GCode() : 
+    GCodeGenerator() : 
     	m_origin(Vec2d::Zero()),
         m_enable_loop_clipping(true), 
         m_enable_cooling_markers(false), 
@@ -153,7 +95,7 @@ public:
         m_silent_time_estimator_enabled(false),
         m_last_obj_copy(nullptr, Point(std::numeric_limits<coord_t>::max(), std::numeric_limits<coord_t>::max()))
         {}
-    ~GCode() = default;
+    ~GCodeGenerator() = default;
 
     // throws std::runtime_exception on error,
     // throws CanceledException through print->throw_if_canceled().
@@ -165,9 +107,19 @@ public:
     void            set_origin(const coordf_t x, const coordf_t y) { this->set_origin(Vec2d(x, y)); }
     const Point&    last_pos() const { return m_last_pos; }
     // Convert coordinates of the active object to G-code coordinates, possibly adjusted for extruder offset.
-    Vec2d           point_to_gcode(const Point &point) const;
+    template<typename Derived>
+    Vec2d           point_to_gcode(const Eigen::MatrixBase<Derived> &point) const {
+        static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "GCodeGenerator::point_to_gcode(): first parameter is not a 2D vector");
+        return Vec2d(unscaled<double>(point.x()), unscaled<double>(point.y())) + m_origin 
+            - m_config.extruder_offset.get_at(m_writer.extruder()->id());
+    }
     // Convert coordinates of the active object to G-code coordinates, possibly adjusted for extruder offset and quantized to G-code resolution.
-    Vec2d           point_to_gcode_quantized(const Point &point) const;
+    template<typename Derived>
+    Vec2d           point_to_gcode_quantized(const Eigen::MatrixBase<Derived> &point) const {
+        static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "GCodeGenerator::point_to_gcode_quantized(): first parameter is not a 2D vector");
+        Vec2d p = this->point_to_gcode(point);
+        return { GCodeFormatter::quantize_xyzf(p.x()), GCodeFormatter::quantize_xyzf(p.y()) };
+    }
     Point           gcode_to_point(const Vec2d &point) const;
     const FullPrintConfig &config() const { return m_config; }
     const Layer*    layer() const { return m_layer; }
@@ -250,6 +202,7 @@ private:
         // Set of object & print layers of the same PrintObject and with the same print_z.
         const ObjectsLayerToPrint       &layers,
         const LayerTools  				&layer_tools,
+        const GCode::SmoothPathCaches   &smooth_path_caches,
         const bool                       last_layer,
 		// Pairs of PrintObject index and its instance index.
 		const std::vector<const PrintInstance*> *ordering,
@@ -264,6 +217,7 @@ private:
         const ToolOrdering                                            &tool_ordering,
         const std::vector<const PrintInstance*>                       &print_object_instances_ordering,
         const std::vector<std::pair<coordf_t, ObjectsLayerToPrint>>   &layers_to_print,
+        const GCode::SmoothPathCache                                  &smooth_path_cache_global,
         GCodeOutputStream                                             &output_stream);
     // Process all layers of a single object instance (sequential mode) with a parallel pipeline:
     // Generate G-code, run the filters (vase mode, cooling buffer), run the G-code analyser
@@ -273,6 +227,7 @@ private:
         const ToolOrdering                      &tool_ordering,
         ObjectsLayerToPrint                      layers_to_print,
         const size_t                             single_object_idx,
+        const GCode::SmoothPathCache            &smooth_path_cache_global,
         GCodeOutputStream                       &output_stream);
 
     void            set_last_pos(const Point &pos) { m_last_pos = pos; m_last_pos_defined = true; }
@@ -280,10 +235,13 @@ private:
     void            set_extruders(const std::vector<unsigned int> &extruder_ids);
     std::string     preamble();
     std::string     change_layer(coordf_t print_z);
-    std::string     extrude_entity(const ExtrusionEntity &entity, const std::string_view description, double speed = -1.);
-    std::string     extrude_loop(ExtrusionLoop loop, const std::string_view description, double speed = -1.);
-    std::string     extrude_multi_path(ExtrusionMultiPath multipath, const std::string_view description, double speed = -1.);
-    std::string     extrude_path(ExtrusionPath path, const std::string_view description, double speed = -1.);
+    std::string     extrude_entity(const ExtrusionEntityReference &entity, const GCode::SmoothPathCache &smooth_path_cache, const std::string_view description, double speed = -1.);
+    std::string     extrude_loop(const ExtrusionLoop &loop, const GCode::SmoothPathCache &smooth_path_cache, const std::string_view description, double speed = -1.);
+    std::string     extrude_skirt(const ExtrusionLoop &loop_src, const ExtrusionFlow &extrusion_flow_override,
+        const GCode::SmoothPathCache &smooth_path_cache, const std::string_view description, double speed);
+
+    std::string     extrude_multi_path(const ExtrusionMultiPath &multipath, bool reverse, const GCode::SmoothPathCache &smooth_path_cache, const std::string_view description, double speed = -1.);
+    std::string     extrude_path(const ExtrusionPath &path, bool reverse, const GCode::SmoothPathCache &smooth_path_cache, const std::string_view description, double speed = -1.);
 
     struct InstanceToPrint
     {
@@ -317,12 +275,14 @@ private:
         const ObjectLayerToPrint &layer_to_print, 
         // Container for extruder overrides (when wiping into object or infill).
         const LayerTools         &layer_tools,
+        // Optional smooth path interpolating extrusion polylines.
+        const GCode::SmoothPathCache &smooth_path_cache,
         // Is any extrusion possibly marked as wiping extrusion?
         const bool                is_anything_overridden, 
         // Round 1 (wiping into object or infill) or round 2 (normal extrusions).
         const bool                print_wipe_extrusions);
 
-    std::string     extrude_support(const ExtrusionEntityCollection &support_fills);
+    std::string     extrude_support(const ExtrusionEntityReferences &support_fills, const GCode::SmoothPathCache &smooth_path_cache);
 
     std::string     travel_to(const Point &point, ExtrusionRole role, std::string comment);
     bool            needs_retraction(const Polyline &travel, ExtrusionRole role = ExtrusionRole::None);
@@ -333,8 +293,6 @@ private:
     // Cache for custom seam enforcers/blockers for each layer.
     SeamPlacer                          m_seam_placer;
 
-    ExtrusionQualityEstimator           m_extrusion_quality_estimator;
-
     /* Origin of print coordinates expressed in unscaled G-code coordinates.
        This affects the input arguments supplied to the extrude*() and travel_to()
        methods. */
@@ -375,7 +333,7 @@ private:
     } m_placeholder_parser_integration;
 
     OozePrevention                      m_ooze_prevention;
-    Wipe                                m_wipe;
+    GCode::Wipe                         m_wipe;
     AvoidCrossingPerimeters             m_avoid_crossing_perimeters;
     JPSPathFinder                       m_avoid_crossing_curled_overhangs;
     RetractWhenCrossingPerimeters       m_retract_when_crossing_perimeters;
@@ -418,7 +376,7 @@ private:
     std::unique_ptr<SpiralVase>         m_spiral_vase;
     std::unique_ptr<GCodeFindReplace>   m_find_replace;
     std::unique_ptr<PressureEqualizer>  m_pressure_equalizer;
-    std::unique_ptr<WipeTowerIntegration> m_wipe_tower;
+    std::unique_ptr<GCode::WipeTowerIntegration> m_wipe_tower;
 
     // Heights (print_z) at which the skirt has already been extruded.
     std::vector<coordf_t>               m_skirt_done;
@@ -434,7 +392,8 @@ private:
     // Processor
     GCodeProcessor                      m_processor;
 
-    std::string                         _extrude(const ExtrusionPath &path, const std::string_view description, double speed = -1);
+    std::string                         _extrude(
+        const ExtrusionAttributes &attribs, const Geometry::ArcWelder::Path &path, const std::string_view description, double speed = -1);
     void                                print_machine_envelope(GCodeOutputStream &file, Print &print);
     void                                _print_first_layer_bed_temperature(GCodeOutputStream &file, Print &print, const std::string &gcode, unsigned int first_printing_extruder_id, bool wait);
     void                                _print_first_layer_extruder_temperatures(GCodeOutputStream &file, Print &print, const std::string &gcode, unsigned int first_printing_extruder_id, bool wait);
@@ -443,8 +402,12 @@ private:
     // To control print speed of 1st object layer over raft interface.
     bool                                object_layer_over_raft() const { return m_object_layer_over_raft; }
 
-    friend class Wipe;
-    friend class WipeTowerIntegration;
+    // Fill in cache of smooth paths for perimeters, fills and supports of the given object layers.
+    // Based on params, the paths are either decimated to sparser polylines, or interpolated with circular arches.
+    static void                         smooth_path_interpolate(const ObjectLayerToPrint &layers, const GCode::SmoothPathCache::InterpolationParameters &params, GCode::SmoothPathCache &out);
+
+    friend class GCode::Wipe;
+    friend class GCode::WipeTowerIntegration;
     friend class PressureEqualizer;
 };
 

src/libslic3r/GCode/AvoidCrossingPerimeters.cpp

@@ -730,7 +730,7 @@ static bool any_expolygon_contains(const ExPolygons &ex_polygons, const std::vec
     return false;
 }
 
-static bool need_wipe(const GCode                    &gcodegen,
+static bool need_wipe(const GCodeGenerator           &gcodegen,
                       const ExPolygons               &lslices_offset,
                       const std::vector<BoundingBox> &lslices_offset_bboxes,
                       const EdgeGrid::Grid           &grid_lslices_offset,
@@ -1167,7 +1167,7 @@ static void init_boundary(AvoidCrossingPerimeters::Boundary *boundary, Polygons
 }
 
 // Plan travel, which avoids perimeter crossings by following the boundaries of the layer.
-Polyline AvoidCrossingPerimeters::travel_to(const GCode &gcodegen, const Point &point, bool *could_be_wipe_disabled)
+Polyline AvoidCrossingPerimeters::travel_to(const GCodeGenerator &gcodegen, const Point &point, bool *could_be_wipe_disabled)
 {
     // If use_external, then perform the path planning in the world coordinate system (correcting for the gcodegen offset).
     // Otherwise perform the path planning in the coordinate system of the active object.
@@ -1470,7 +1470,7 @@ static size_t avoid_perimeters(const AvoidCrossingPerimeters::Boundary &boundary
 }
 
 // Plan travel, which avoids perimeter crossings by following the boundaries of the layer.
-Polyline AvoidCrossingPerimeters::travel_to(const GCode &gcodegen, const Point &point, bool *could_be_wipe_disabled)
+Polyline AvoidCrossingPerimeters::travel_to(const GCodeGenerator &gcodegen, const Point &point, bool *could_be_wipe_disabled)
 {
     // If use_external, then perform the path planning in the world coordinate system (correcting for the gcodegen offset).
     // Otherwise perform the path planning in the coordinate system of the active object.

src/libslic3r/GCode/AvoidCrossingPerimeters.hpp

@@ -8,7 +8,7 @@
 namespace Slic3r {
 
 // Forward declarations.
-class GCode;
+class GCodeGenerator;
 class Layer;
 class Point;
 
@@ -25,13 +25,13 @@ public:
 
     void        init_layer(const Layer &layer);
 
-    Polyline    travel_to(const GCode& gcodegen, const Point& point)
+    Polyline    travel_to(const GCodeGenerator &gcodegen, const Point& point)
     {
         bool could_be_wipe_disabled;
         return this->travel_to(gcodegen, point, &could_be_wipe_disabled);
     }
 
-    Polyline    travel_to(const GCode& gcodegen, const Point& point, bool* could_be_wipe_disabled);
+    Polyline    travel_to(const GCodeGenerator &gcodegen, const Point& point, bool* could_be_wipe_disabled);
 
     struct Boundary {
         // Collection of boundaries used for detection of crossing perimeters for travels

src/libslic3r/GCode/ConflictChecker.hpp

@@ -43,7 +43,7 @@ public:
     void raise()
     {
         if (valid()) {
-            if (_piles[_curPileIdx].empty() == false) { _curHeight += _piles[_curPileIdx].front().height; }
+            if (_piles[_curPileIdx].empty() == false) { _curHeight += _piles[_curPileIdx].front().height(); }
             _curPileIdx++;
         }
     }

src/libslic3r/GCode/CoolingBuffer.cpp

@@ -19,7 +19,7 @@
 
 namespace Slic3r {
 
-CoolingBuffer::CoolingBuffer(GCode &gcodegen) : m_config(gcodegen.config()), m_toolchange_prefix(gcodegen.writer().toolchange_prefix()), m_current_extruder(0)
+CoolingBuffer::CoolingBuffer(GCodeGenerator &gcodegen) : m_config(gcodegen.config()), m_toolchange_prefix(gcodegen.writer().toolchange_prefix()), m_current_extruder(0)
 {
     this->reset(gcodegen.writer().get_position());
 
@@ -33,36 +33,45 @@ CoolingBuffer::CoolingBuffer(GCode &gcodegen) : m_config(gcodegen.config()), m_t
 
 void CoolingBuffer::reset(const Vec3d &position)
 {
-    m_current_pos.assign(5, 0.f);
-    m_current_pos[0] = float(position.x());
-    m_current_pos[1] = float(position.y());
-    m_current_pos[2] = float(position.z());
-    m_current_pos[4] = float(m_config.travel_speed.value);
+    assert(m_current_pos.size() == 5);
+    m_current_pos[AxisIdx::X] = float(position.x());
+    m_current_pos[AxisIdx::Y] = float(position.y());
+    m_current_pos[AxisIdx::Z] = float(position.z());
+    m_current_pos[AxisIdx::E] = 0.f;
+    m_current_pos[AxisIdx::F] = float(m_config.travel_speed.value);
     m_fan_speed = -1;
 }
 
 struct CoolingLine
 {
-    enum Type {
+    enum Type : uint32_t {
         TYPE_SET_TOOL           = 1 << 0,
         TYPE_EXTRUDE_END        = 1 << 1,
         TYPE_BRIDGE_FAN_START   = 1 << 2,
         TYPE_BRIDGE_FAN_END     = 1 << 3,
         TYPE_G0                 = 1 << 4,
         TYPE_G1                 = 1 << 5,
-        TYPE_ADJUSTABLE         = 1 << 6,
-        TYPE_EXTERNAL_PERIMETER = 1 << 7,
+        // G2 or G3: Arc interpolation
+        TYPE_G2G3               = 1 << 6,
+        TYPE_ADJUSTABLE         = 1 << 7,
+        TYPE_EXTERNAL_PERIMETER = 1 << 8,
+        // Arc interpolation, counter-clockwise.
+        TYPE_G2G3_CCW           = 1 << 9,
+        // Arc interpolation, arc defined by IJ (offset of arc center from its start position).
+        TYPE_G2G3_IJ            = 1 << 10,
+        // Arc interpolation, arc defined by R (arc radius, positive - smaller, negative - larger).
+        TYPE_G2G3_R             = 1 << 11,
         // The line sets a feedrate.
-        TYPE_HAS_F              = 1 << 8,
-        TYPE_WIPE               = 1 << 9,
-        TYPE_G4                 = 1 << 10,
-        TYPE_G92                = 1 << 11,
+        TYPE_HAS_F              = 1 << 12,
+        TYPE_WIPE               = 1 << 13,
+        TYPE_G4                 = 1 << 14,
+        TYPE_G92                = 1 << 15,
         // Would be TYPE_ADJUSTABLE, but the block of G-code lines has zero extrusion length, thus the block
         // cannot have its speed adjusted. This should not happen (sic!).
-        TYPE_ADJUSTABLE_EMPTY   = 1 << 12,
+        TYPE_ADJUSTABLE_EMPTY   = 1 << 16,
         // Custom fan speed (introduced for overhang fan speed)
-        TYPE_SET_FAN_SPEED      = 1 << 13,
-        TYPE_RESET_FAN_SPEED    = 1 << 14,
+        TYPE_SET_FAN_SPEED      = 1 << 17,
+        TYPE_RESET_FAN_SPEED    = 1 << 18,
     };
 
     CoolingLine(unsigned int type, size_t  line_start, size_t  line_end) :
@@ -324,7 +333,7 @@ std::string CoolingBuffer::process_layer(std::string &&gcode, size_t layer_id, b
 
 // Parse the layer G-code for the moves, which could be adjusted.
 // Return the list of parsed lines, bucketed by an extruder.
-std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::string &gcode, std::vector<float> &current_pos) const
+std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::string &gcode, std::array<float, 5> &current_pos) const
 {
     std::vector<PerExtruderAdjustments> per_extruder_adjustments(m_extruder_ids.size());
     std::vector<size_t>                 map_extruder_to_per_extruder_adjustment(m_num_extruders, 0);
@@ -347,7 +356,7 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
     // for a sequence of extrusion moves.
     size_t            active_speed_modifier = size_t(-1);
 
-    std::vector<float> new_pos;
+    std::array<float, AxisIdx::Count> new_pos;
     for (; *line_start != 0; line_start = line_end) 
     {
         while (*line_end != '\n' && *line_end != 0)
@@ -362,12 +371,20 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
             line.type = CoolingLine::TYPE_G0;
         else if (boost::starts_with(sline, "G1 "))
             line.type = CoolingLine::TYPE_G1;
+        else if (boost::starts_with(sline, "G2 "))
+            // Arc, clockwise.
+            line.type = CoolingLine::TYPE_G2G3;
+        else if (boost::starts_with(sline, "G3 "))
+            // Arc, counter-clockwise.
+            line.type = CoolingLine::TYPE_G2G3 | CoolingLine::TYPE_G2G3_CCW;
         else if (boost::starts_with(sline, "G92 "))
             line.type = CoolingLine::TYPE_G92;
         if (line.type) {
-            // G0, G1 or G92
+            // G0, G1, G2, G3 or G92
+            // Initialize current_pos from new_pos, set IJKR to zero.
+            std::fill(std::copy(std::begin(current_pos), std::end(current_pos), std::begin(new_pos)),
+                std::end(new_pos), 0.f);
             // Parse the G-code line.
-            new_pos = current_pos;
             for (auto c = sline.begin() + 3;;) {
                 // Skip whitespaces.
                 for (; c != sline.end() && (*c == ' ' || *c == '\t'); ++ c);
@@ -376,21 +393,31 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
 
                 // Parse the axis.
                 size_t axis = (*c >= 'X' && *c <= 'Z') ? (*c - 'X') :
-                              (*c == extrusion_axis) ? 3 : (*c == 'F') ? 4 : size_t(-1);
+                              (*c == extrusion_axis) ? AxisIdx::E : (*c == 'F') ? AxisIdx::F : 
+                              (*c >= 'I' && *c <= 'K') ? int(AxisIdx::I) + (*c - 'I') : 
+                              (*c == 'R') ? AxisIdx::R : size_t(-1);
                 if (axis != size_t(-1)) {
                     //auto [pend, ec] = 
                         fast_float::from_chars(&*(++ c), sline.data() + sline.size(), new_pos[axis]);
-                    if (axis == 4) {
+                    if (axis == AxisIdx::F) {
                         // Convert mm/min to mm/sec.
-                        new_pos[4] /= 60.f;
+                        new_pos[AxisIdx::F] /= 60.f;
                         if ((line.type & CoolingLine::TYPE_G92) == 0)
                             // This is G0 or G1 line and it sets the feedrate. This mark is used for reducing the duplicate F calls.
                             line.type |= CoolingLine::TYPE_HAS_F;
-                    }
+                    } else if (axis >= AxisIdx::I && axis <= AxisIdx::J)
+                        line.type |= CoolingLine::TYPE_G2G3_IJ;
+                    else if (axis == AxisIdx::R)
+                        line.type |= CoolingLine::TYPE_G2G3_R;
                 }
                 // Skip this word.
                 for (; c != sline.end() && *c != ' ' && *c != '\t'; ++ c);
             }
+            // If G2 or G3, then either center of the arc or radius has to be defined.
+            assert(! (line.type & CoolingLine::TYPE_G2G3) ||
+                (line.type & (CoolingLine::TYPE_G2G3_IJ | CoolingLine::TYPE_G2G3_R)));
+            // Arc is defined either by IJ or by R, not by both.
+            assert(! ((line.type & CoolingLine::TYPE_G2G3_IJ) && (line.type & CoolingLine::TYPE_G2G3_R)));
             bool external_perimeter = boost::contains(sline, ";_EXTERNAL_PERIMETER");
             bool wipe               = boost::contains(sline, ";_WIPE");
             if (external_perimeter)
@@ -402,23 +429,41 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
                 active_speed_modifier = adjustment->lines.size();
             }
             if ((line.type & CoolingLine::TYPE_G92) == 0) {
-                // G0 or G1. Calculate the duration.
+                // G0, G1, G2, G3. Calculate the duration.
+                assert((line.type & CoolingLine::TYPE_G0) != 0 + (line.type & CoolingLine::TYPE_G1) != 0 + (line.type & CoolingLine::TYPE_G2G3) != 0 == 1);
                 if (m_config.use_relative_e_distances.value)
                     // Reset extruder accumulator.
-                    current_pos[3] = 0.f;
+                    current_pos[AxisIdx::E] = 0.f;
                 float dif[4];
                 for (size_t i = 0; i < 4; ++ i)
                     dif[i] = new_pos[i] - current_pos[i];
-                float dxy2 = dif[0] * dif[0] + dif[1] * dif[1];
-                float dxyz2 = dxy2 + dif[2] * dif[2];
+                float dxy2;
+                if (line.type & CoolingLine::TYPE_G2G3) {
+                    // Measure arc length.
+                    if (line.type & CoolingLine::TYPE_G2G3_IJ) {
+                        dxy2 = sqr(Geometry::ArcWelder::arc_length(
+                            Vec2d(current_pos[AxisIdx::X], current_pos[AxisIdx::Y]),
+                            Vec2d(new_pos[AxisIdx::X], new_pos[AxisIdx::Y]),
+                            Vec2d(current_pos[AxisIdx::X] + new_pos[AxisIdx::I], current_pos[AxisIdx::Y] + new_pos[AxisIdx::J]),
+                            line.type & CoolingLine::TYPE_G2G3_CCW));
+                    } else if (line.type & CoolingLine::TYPE_G2G3_R) {
+                        dxy2 = sqr(Geometry::ArcWelder::arc_length(
+                            Vec2d(current_pos[AxisIdx::X], current_pos[AxisIdx::Y]),
+                            Vec2d(new_pos[AxisIdx::X], new_pos[AxisIdx::Y]),
+                            double(new_pos[AxisIdx::R])));
+                    } else
+                        dxy2 = 0;
+                } else
+                    dxy2 = sqr(dif[AxisIdx::X]) + sqr(dif[AxisIdx::Y]);
+                float dxyz2 = dxy2 + sqr(dif[AxisIdx::Z]);
                 if (dxyz2 > 0.f) {
                     // Movement in xyz, calculate time from the xyz Euclidian distance.
                     line.length = sqrt(dxyz2);
-                } else if (std::abs(dif[3]) > 0.f) {
+                } else if (std::abs(dif[AxisIdx::E]) > 0.f) {
                     // Movement in the extruder axis.
-                    line.length = std::abs(dif[3]);
+                    line.length = std::abs(dif[AxisIdx::E]);
                 }
-                line.feedrate = new_pos[4];
+                line.feedrate = new_pos[AxisIdx::F];
                 assert((line.type & CoolingLine::TYPE_ADJUSTABLE) == 0 || line.feedrate > 0.f);
                 if (line.length > 0) {
                     assert(line.feedrate > 0);
@@ -430,7 +475,7 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
                     assert(adjustment->min_print_speed >= 0);
                     line.time_max = (adjustment->min_print_speed == 0.f) ? FLT_MAX : std::max(line.time, line.length / adjustment->min_print_speed);
                 }
-                if (active_speed_modifier < adjustment->lines.size() && (line.type & CoolingLine::TYPE_G1)) {
+                if (active_speed_modifier < adjustment->lines.size() && (line.type & (CoolingLine::TYPE_G1 | CoolingLine::TYPE_G2G3))) {
                     // Inside the ";_EXTRUDE_SET_SPEED" blocks, there must not be a G1 Fxx entry.
                     assert((line.type & CoolingLine::TYPE_HAS_F) == 0);
                     CoolingLine &sm = adjustment->lines[active_speed_modifier];
@@ -447,7 +492,7 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
                     line.type = 0;
                 }
             }
-            current_pos = std::move(new_pos);
+            std::copy(std::begin(new_pos), std::begin(new_pos) + 5, std::begin(current_pos));
         } else if (boost::starts_with(sline, ";_EXTRUDE_END")) {
             // Closing a block of non-zero length extrusion moves.
             line.type = CoolingLine::TYPE_EXTRUDE_END;

src/libslic3r/GCode/CoolingBuffer.hpp

@@ -7,7 +7,7 @@
 
 namespace Slic3r {
 
-class GCode;
+class GCodeGenerator;
 class Layer;
 struct PerExtruderAdjustments;
 
@@ -22,7 +22,7 @@ struct PerExtruderAdjustments;
 //
 class CoolingBuffer {
 public:
-    CoolingBuffer(GCode &gcodegen);
+    CoolingBuffer(GCodeGenerator &gcodegen);
     void        reset(const Vec3d &position);
     void        set_current_extruder(unsigned int extruder_id) { m_current_extruder = extruder_id; }
     std::string process_layer(std::string &&gcode, size_t layer_id, bool flush);
@@ -31,7 +31,7 @@ public:
 
 private:
 	CoolingBuffer& operator=(const CoolingBuffer&) = delete;
-    std::vector<PerExtruderAdjustments> parse_layer_gcode(const std::string &gcode, std::vector<float> &current_pos) const;
+    std::vector<PerExtruderAdjustments> parse_layer_gcode(const std::string &gcode, std::array<float, 5> &current_pos) const;
     float       calculate_layer_slowdown(std::vector<PerExtruderAdjustments> &per_extruder_adjustments);
     // Apply slow down over G-code lines stored in per_extruder_adjustments, enable fan if needed.
     // Returns the adjusted G-code.
@@ -40,9 +40,11 @@ private:
     // G-code snippet cached for the support layers preceding an object layer.
     std::string                 m_gcode;
     // Internal data.
-    // X,Y,Z,E,F
     std::vector<char>           m_axis;
-    std::vector<float>          m_current_pos;
+    enum AxisIdx : int {
+        X = 0, Y, Z, E, F, I, J, K, R, Count
+    };
+    std::array<float, 5>        m_current_pos;
     // Current known fan speed or -1 if not known yet.
     int                         m_fan_speed;
     // Cached from GCodeWriter.
@@ -51,7 +53,7 @@ private:
     // Highest of m_extruder_ids plus 1.
     unsigned int                m_num_extruders { 0 };
     const std::string           m_toolchange_prefix;
-    // Referencs GCode::m_config, which is FullPrintConfig. While the PrintObjectConfig slice of FullPrintConfig is being modified,
+    // Referencs GCodeGenerator::m_config, which is FullPrintConfig. While the PrintObjectConfig slice of FullPrintConfig is being modified,
     // the PrintConfig slice of FullPrintConfig is constant, thus no thread synchronization is required.
     const PrintConfig          &m_config;
     unsigned int                m_current_extruder;

src/libslic3r/GCode/ExtrusionProcessor.cpp

@@ -0,0 +1,216 @@
+#include "ExtrusionProcessor.hpp"
+#include <string>
+
+namespace Slic3r { namespace ExtrusionProcessor {
+
+ExtrusionPaths calculate_and_split_overhanging_extrusions(const ExtrusionPath                             &path,
+                                                          const AABBTreeLines::LinesDistancer<Linef>      &unscaled_prev_layer,
+                                                          const AABBTreeLines::LinesDistancer<CurledLine> &prev_layer_curled_lines)
+{
+    std::vector<ExtendedPoint>           extended_points = estimate_points_properties<true, true, true, true>(path.polyline.points,
+                                                                                                    unscaled_prev_layer, path.width());
+    std::vector<std::pair<float, float>> calculated_distances(extended_points.size());
+
+    for (size_t i = 0; i < extended_points.size(); i++) {
+        const ExtendedPoint &curr = extended_points[i];
+        const ExtendedPoint &next = extended_points[i + 1 < extended_points.size() ? i + 1 : i];
+
+        // The following code artifically increases the distance to provide slowdown for extrusions that are over curled lines
+        float        proximity_to_curled_lines = 0.0;
+        const double dist_limit                = 10.0 * path.width();
+        {
+            Vec2d middle       = 0.5 * (curr.position + next.position);
+            auto  line_indices = prev_layer_curled_lines.all_lines_in_radius(Point::new_scale(middle), scale_(dist_limit));
+            if (!line_indices.empty()) {
+                double len = (next.position - curr.position).norm();
+                // For long lines, there is a problem with the additional slowdown. If by accident, there is small curled line near the middle
+                // of this long line
+                //  The whole segment gets slower unnecesarily. For these long lines, we do additional check whether it is worth slowing down.
+                // NOTE that this is still quite rough approximation, e.g. we are still checking lines only near the middle point
+                // TODO maybe split the lines into smaller segments before running this alg? but can be demanding, and GCode will be huge
+                if (len > 8) {
+                    Vec2d dir   = Vec2d(next.position - curr.position) / len;
+                    Vec2d right = Vec2d(-dir.y(), dir.x());
+
+                    Polygon box_of_influence = {
+                        scaled(Vec2d(curr.position + right * dist_limit)),
+                        scaled(Vec2d(next.position + right * dist_limit)),
+                        scaled(Vec2d(next.position - right * dist_limit)),
+                        scaled(Vec2d(curr.position - right * dist_limit)),
+                    };
+
+                    double projected_lengths_sum = 0;
+                    for (size_t idx : line_indices) {
+                        const CurledLine &line   = prev_layer_curled_lines.get_line(idx);
+                        Lines             inside = intersection_ln({{line.a, line.b}}, {box_of_influence});
+                        if (inside.empty())
+                            continue;
+                        double projected_length = abs(dir.dot(unscaled(Vec2d((inside.back().b - inside.back().a).cast<double>()))));
+                        projected_lengths_sum += projected_length;
+                    }
+                    if (projected_lengths_sum < 0.4 * len) {
+                        line_indices.clear();
+                    }
+                }
+
+                for (size_t idx : line_indices) {
+                    const CurledLine &line                 = prev_layer_curled_lines.get_line(idx);
+                    float             distance_from_curled = unscaled(line_alg::distance_to(line, Point::new_scale(middle)));
+                    float proximity = (1.0 - (distance_from_curled / dist_limit)) * (1.0 - (distance_from_curled / dist_limit)) *
+                                      (line.curled_height / (path.height() * 10.0f)); // max_curled_height_factor from SupportSpotGenerator
+                    proximity_to_curled_lines = std::max(proximity_to_curled_lines, proximity);
+                }
+            }
+        }
+        calculated_distances[i].first  = std::max(curr.distance, next.distance);
+        calculated_distances[i].second = proximity_to_curled_lines;
+    }
+
+    ExtrusionPaths      result;
+    ExtrusionAttributes new_attrs = path.attributes();
+    new_attrs.overhang_attributes = std::optional<OverhangAttributes>(
+        {calculated_distances[0].first, calculated_distances[0].first, calculated_distances[0].second});
+    result.emplace_back(new_attrs);
+    result.back().polyline.append(Point::new_scale(extended_points[0].position));
+    size_t sequence_start_index = 0;
+    for (size_t i = 1; i < extended_points.size(); i++) {
+        result.back().polyline.append(Point::new_scale(extended_points[i].position));
+        result.back().overhang_attributes_mutable()->end_distance_from_prev_layer = extended_points[i].distance;
+
+        if (std::abs(calculated_distances[sequence_start_index].first - calculated_distances[i].first) < 0.001 * path.attributes().width &&
+            std::abs(calculated_distances[sequence_start_index].second - calculated_distances[i].second) < 0.001) {
+            // do not start new path, the attributes are similar enough
+            // NOTE: a larger tolerance may be applied here. However, it makes the gcode preview much less smooth
+            // (But it has very likely zero impact on the print quality.)
+        } else if (i + 1 < extended_points.size()) { // do not start new path if this is last point!
+            // start new path, parameters differ
+            new_attrs.overhang_attributes->start_distance_from_prev_layer = calculated_distances[i].first;
+            new_attrs.overhang_attributes->end_distance_from_prev_layer   = calculated_distances[i].first;
+            new_attrs.overhang_attributes->proximity_to_curled_lines      = calculated_distances[i].second;
+            sequence_start_index                                          = i;
+            result.emplace_back(new_attrs);
+            result.back().polyline.append(Point::new_scale(extended_points[i].position));
+        }
+    }
+
+    return result;
+};
+
+ExtrusionEntityCollection calculate_and_split_overhanging_extrusions(const ExtrusionEntityCollection            *ecc,
+                                                                     const AABBTreeLines::LinesDistancer<Linef> &unscaled_prev_layer,
+                                                                     const AABBTreeLines::LinesDistancer<CurledLine> &prev_layer_curled_lines)
+{
+    ExtrusionEntityCollection result{};
+    result.no_sort = ecc->no_sort;
+    for (const auto *e : ecc->entities) {
+        if (auto *col = dynamic_cast<const ExtrusionEntityCollection *>(e)) {
+            result.append(calculate_and_split_overhanging_extrusions(col, unscaled_prev_layer, prev_layer_curled_lines));
+        } else if (auto *loop = dynamic_cast<const ExtrusionLoop *>(e)) {
+            ExtrusionLoop new_loop = *loop;
+            new_loop.paths.clear();
+            for (const ExtrusionPath &p : loop->paths) {
+                auto paths = calculate_and_split_overhanging_extrusions(p, unscaled_prev_layer, prev_layer_curled_lines);
+                new_loop.paths.insert(new_loop.paths.end(), paths.begin(), paths.end());
+            }
+            result.append(new_loop);
+        } else if (auto *mp = dynamic_cast<const ExtrusionMultiPath *>(e)) {
+            ExtrusionMultiPath new_mp = *mp;
+            new_mp.paths.clear();
+            for (const ExtrusionPath &p : mp->paths) {
+                auto paths = calculate_and_split_overhanging_extrusions(p, unscaled_prev_layer, prev_layer_curled_lines);
+                new_mp.paths.insert(new_mp.paths.end(), paths.begin(), paths.end());
+            }
+            result.append(new_mp);
+        } else if (auto *op = dynamic_cast<const ExtrusionPathOriented *>(e)) {
+            auto paths = calculate_and_split_overhanging_extrusions(*op, unscaled_prev_layer, prev_layer_curled_lines);
+            for (const ExtrusionPath &p : paths) {
+                result.append(ExtrusionPathOriented(p.polyline, p.attributes()));
+            }
+        } else if (auto *p = dynamic_cast<const ExtrusionPath *>(e)) {
+            auto paths = calculate_and_split_overhanging_extrusions(*p, unscaled_prev_layer, prev_layer_curled_lines);
+            result.append(paths);
+        } else {
+            throw Slic3r::InvalidArgument("Unknown extrusion entity type");
+        }
+    }
+    return result;
+};
+
+
+std::pair<float,float> calculate_overhang_speed(const ExtrusionAttributes &attributes,
+                              const FullPrintConfig     &config,
+                              size_t                     extruder_id,
+                              float                      external_perim_reference_speed,
+                              float                      default_speed)
+{
+    assert(attributes.overhang_attributes.has_value());
+    std::vector<std::pair<int, ConfigOptionFloatOrPercent>> overhangs_with_speeds = {
+        {100, ConfigOptionFloatOrPercent{default_speed, false}}};
+    if (config.enable_dynamic_overhang_speeds) {
+        overhangs_with_speeds = {{0, config.overhang_speed_0},
+                                 {25, config.overhang_speed_1},
+                                 {50, config.overhang_speed_2},
+                                 {75, config.overhang_speed_3},
+                                 {100, ConfigOptionFloatOrPercent{default_speed, false}}};
+    }
+
+    std::vector<std::pair<int, ConfigOptionInts>> overhang_with_fan_speeds = {{100, ConfigOptionInts{0}}};
+    if (config.enable_dynamic_fan_speeds.get_at(extruder_id)) {
+        overhang_with_fan_speeds = {{0, config.overhang_fan_speed_0},
+                                    {25, config.overhang_fan_speed_1},
+                                    {50, config.overhang_fan_speed_2},
+                                    {75, config.overhang_fan_speed_3},
+                                    {100, ConfigOptionInts{0}}};
+    }
+
+    float                  speed_base = external_perim_reference_speed > 0 ? external_perim_reference_speed : default_speed;
+    std::map<float, float> speed_sections;
+    for (size_t i = 0; i < overhangs_with_speeds.size(); i++) {
+        float distance = attributes.width * (1.0 - (overhangs_with_speeds[i].first / 100.0));
+        float speed    = overhangs_with_speeds[i].second.percent ? (speed_base * overhangs_with_speeds[i].second.value / 100.0) :
+                                                                   overhangs_with_speeds[i].second.value;
+        if (speed < EPSILON)
+            speed = speed_base;
+        speed_sections[distance] = speed;
+    }
+
+    std::map<float, float> fan_speed_sections;
+    for (size_t i = 0; i < overhang_with_fan_speeds.size(); i++) {
+        float distance               = attributes.width * (1.0 - (overhang_with_fan_speeds[i].first / 100.0));
+        float fan_speed              = overhang_with_fan_speeds[i].second.get_at(extruder_id);
+        fan_speed_sections[distance] = fan_speed;
+    }
+
+    auto interpolate_speed = [](const std::map<float, float> &values, float distance) {
+        auto upper_dist = values.lower_bound(distance);
+        if (upper_dist == values.end()) {
+            return values.rbegin()->second;
+        }
+        if (upper_dist == values.begin()) {
+            return upper_dist->second;
+        }
+
+        auto  lower_dist = std::prev(upper_dist);
+        float t          = (distance - lower_dist->first) / (upper_dist->first - lower_dist->first);
+        return (1.0f - t) * lower_dist->second + t * upper_dist->second;
+    };
+
+    float extrusion_speed   = std::min(interpolate_speed(speed_sections, attributes.overhang_attributes->start_distance_from_prev_layer),
+                                       interpolate_speed(speed_sections, attributes.overhang_attributes->end_distance_from_prev_layer));
+    float curled_base_speed = interpolate_speed(speed_sections,
+                                                attributes.width * attributes.overhang_attributes->proximity_to_curled_lines);
+    float final_speed       = std::min(curled_base_speed, extrusion_speed);
+    float fan_speed = std::min(interpolate_speed(fan_speed_sections, attributes.overhang_attributes->start_distance_from_prev_layer),
+                               interpolate_speed(fan_speed_sections, attributes.overhang_attributes->end_distance_from_prev_layer));
+
+    if (!config.enable_dynamic_overhang_speeds) {
+        final_speed = -1;
+    }
+    if (!config.enable_dynamic_fan_speeds.get_at(extruder_id)) {
+        fan_speed = -1;
+    }
+
+    return {final_speed, fan_speed};
+}
+
+}} // namespace Slic3r::ExtrusionProcessor

src/libslic3r/GCode/ExtrusionProcessor.hpp

@@ -14,19 +14,23 @@
 #include "../Flow.hpp"
 #include "../Config.hpp"
 #include "../Line.hpp"
+#include "../Exception.hpp"
+#include "../PrintConfig.hpp"
 
 #include <algorithm>
+#include <cassert>
 #include <cmath>
 #include <cstddef>
 #include <iterator>
 #include <limits>
 #include <numeric>
+#include <optional>
 #include <ostream>
 #include <unordered_map>
 #include <utility>
 #include <vector>
 
-namespace Slic3r {
+namespace Slic3r { namespace ExtrusionProcessor {
 
 struct ExtendedPoint
 {
@@ -54,19 +58,22 @@ std::vector<ExtendedPoint> estimate_points_properties(const POINTS
 
     {
         ExtendedPoint start_point{maybe_unscale(input_points.front())};
-        auto [distance, nearest_line, x]    = unscaled_prev_layer.template distance_from_lines_extra<SIGNED_DISTANCE>(start_point.position.cast<AABBScalar>());
+        auto [distance, nearest_line,
+              x] = unscaled_prev_layer.template distance_from_lines_extra<SIGNED_DISTANCE>(start_point.position.cast<AABBScalar>());
         start_point.distance = distance + boundary_offset;
         points.push_back(start_point);
     }
     for (size_t i = 1; i < input_points.size(); i++) {
         ExtendedPoint next_point{maybe_unscale(input_points[i])};
-        auto [distance, nearest_line, x]   = unscaled_prev_layer.template distance_from_lines_extra<SIGNED_DISTANCE>(next_point.position.cast<AABBScalar>());
+        auto [distance, nearest_line,
+              x] = unscaled_prev_layer.template distance_from_lines_extra<SIGNED_DISTANCE>(next_point.position.cast<AABBScalar>());
         next_point.distance = distance + boundary_offset;
 
         if (ADD_INTERSECTIONS &&
             ((points.back().distance > boundary_offset + EPSILON) != (next_point.distance > boundary_offset + EPSILON))) {
             const ExtendedPoint &prev_point    = points.back();
-            auto intersections = unscaled_prev_layer.template intersections_with_line<true>(L{prev_point.position.cast<AABBScalar>(), next_point.position.cast<AABBScalar>()});
+            auto                 intersections = unscaled_prev_layer.template intersections_with_line<true>(
+                L{prev_point.position.cast<AABBScalar>(), next_point.position.cast<AABBScalar>()});
             for (const auto &intersection : intersections) {
                 ExtendedPoint p{};
                 p.position = intersection.first.template cast<double>();
@@ -79,24 +86,25 @@ std::vector<ExtendedPoint> estimate_points_properties(const POINTS
 
     if (PREV_LAYER_BOUNDARY_OFFSET && ADD_INTERSECTIONS) {
         std::vector<ExtendedPoint> new_points;
-        new_points.reserve(points.size()*2);
+        new_points.reserve(points.size() * 2);
         new_points.push_back(points.front());
         for (int point_idx = 0; point_idx < int(points.size()) - 1; ++point_idx) {
             const ExtendedPoint &curr = points[point_idx];
             const ExtendedPoint &next = points[point_idx + 1];
 
-            if ((curr.distance > 0 && curr.distance < boundary_offset + 2.0f) ||
-                (next.distance > 0 && next.distance < boundary_offset + 2.0f)) {
+            if ((curr.distance > -boundary_offset && curr.distance < boundary_offset + 2.0f) ||
+                (next.distance > -boundary_offset && next.distance < boundary_offset + 2.0f)) {
                 double line_len = (next.position - curr.position).norm();
                 if (line_len > 4.0f) {
-                    double a0 = std::clamp((curr.distance + 2 * boundary_offset) / line_len, 0.0, 1.0);
-                    double a1 = std::clamp(1.0f - (next.distance + 2 * boundary_offset) / line_len, 0.0, 1.0);
+                    double a0 = std::clamp((curr.distance + 3 * boundary_offset) / line_len, 0.0, 1.0);
+                    double a1 = std::clamp(1.0f - (next.distance + 3 * boundary_offset) / line_len, 0.0, 1.0);
                     double t0 = std::min(a0, a1);
                     double t1 = std::max(a0, a1);
 
                     if (t0 < 1.0) {
                         auto p0     = curr.position + t0 * (next.position - curr.position);
-                        auto [p0_dist, p0_near_l, p0_x] = unscaled_prev_layer.template distance_from_lines_extra<SIGNED_DISTANCE>(p0.cast<AABBScalar>());
+                        auto [p0_dist, p0_near_l,
+                              p0_x] = unscaled_prev_layer.template distance_from_lines_extra<SIGNED_DISTANCE>(p0.cast<AABBScalar>());
                         ExtendedPoint new_p{};
                         new_p.position = p0;
                         new_p.distance = float(p0_dist + boundary_offset);
@@ -104,7 +112,8 @@ std::vector<ExtendedPoint> estimate_points_properties(const POINTS
                     }
                     if (t1 > 0.0) {
                         auto p1     = curr.position + t1 * (next.position - curr.position);
-                        auto [p1_dist, p1_near_l, p1_x] = unscaled_prev_layer.template distance_from_lines_extra<SIGNED_DISTANCE>(p1.cast<AABBScalar>());
+                        auto [p1_dist, p1_near_l,
+                              p1_x] = unscaled_prev_layer.template distance_from_lines_extra<SIGNED_DISTANCE>(p1.cast<AABBScalar>());
                         ExtendedPoint new_p{};
                         new_p.position = p1;
                         new_p.distance = float(p1_dist + boundary_offset);
@@ -114,12 +123,12 @@ std::vector<ExtendedPoint> estimate_points_properties(const POINTS
             }
             new_points.push_back(next);
         }
-        points = new_points;
+        points = std::move(new_points);
     }
 
     if (max_line_length > 0) {
         std::vector<ExtendedPoint> new_points;
-        new_points.reserve(points.size()*2);
+        new_points.reserve(points.size() * 2);
         {
             for (size_t i = 0; i + 1 < points.size(); i++) {
                 const ExtendedPoint &curr = points[i];
@@ -140,7 +149,7 @@ std::vector<ExtendedPoint> estimate_points_properties(const POINTS
             }
             new_points.push_back(points.back());
         }
-        points = new_points;
+        points = std::move(new_points);
     }
 
     std::vector<float> angles_for_curvature(points.size());
@@ -212,144 +221,21 @@ std::vector<ExtendedPoint> estimate_points_properties(const POINTS
     return points;
 }
 
-struct ProcessedPoint
-{
-    Point p;
-    float speed = 1.0f;
-    int fan_speed = 0;
-};
+ExtrusionPaths calculate_and_split_overhanging_extrusions(const ExtrusionPath                             &path,
+                                                          const AABBTreeLines::LinesDistancer<Linef>      &unscaled_prev_layer,
+                                                          const AABBTreeLines::LinesDistancer<CurledLine> &prev_layer_curled_lines);
 
-class ExtrusionQualityEstimator
-{
-    std::unordered_map<const PrintObject *, AABBTreeLines::LinesDistancer<Linef>> prev_layer_boundaries;
-    std::unordered_map<const PrintObject *, AABBTreeLines::LinesDistancer<Linef>> next_layer_boundaries;
-    std::unordered_map<const PrintObject *, AABBTreeLines::LinesDistancer<CurledLine>> prev_curled_extrusions;
-    std::unordered_map<const PrintObject *, AABBTreeLines::LinesDistancer<CurledLine>> next_curled_extrusions;
-    const PrintObject                                                            *current_object;
+ExtrusionEntityCollection calculate_and_split_overhanging_extrusions(
+    const ExtrusionEntityCollection                 *ecc,
+    const AABBTreeLines::LinesDistancer<Linef>      &unscaled_prev_layer,
+    const AABBTreeLines::LinesDistancer<CurledLine> &prev_layer_curled_lines);
 
-public:
-    void set_current_object(const PrintObject *object) { current_object = object; }
-
-    void prepare_for_new_layer(const Layer *layer)
-    {
-        if (layer == nullptr)
-            return;
-        const PrintObject *object      = layer->object();
-        prev_layer_boundaries[object]  = next_layer_boundaries[object];
-        next_layer_boundaries[object]  = AABBTreeLines::LinesDistancer<Linef>{to_unscaled_linesf(layer->lslices)};
-        prev_curled_extrusions[object] = next_curled_extrusions[object];
-        next_curled_extrusions[object] = AABBTreeLines::LinesDistancer<CurledLine>{layer->curled_lines};
-    }
-
-    std::vector<ProcessedPoint> estimate_speed_from_extrusion_quality(
-        const ExtrusionPath                                          &path,
-        const std::vector<std::pair<int, ConfigOptionFloatOrPercent>> overhangs_w_speeds,
-        const std::vector<std::pair<int, ConfigOptionInts>>           overhangs_w_fan_speeds,
+std::pair<float, float> calculate_overhang_speed(const ExtrusionAttributes &attributes,
+                                                 const FullPrintConfig     &config,
                                                  size_t                     extruder_id,
-        float                                                         ext_perimeter_speed,
-        float                                                         original_speed)
-    {
-        float                  speed_base = ext_perimeter_speed > 0 ? ext_perimeter_speed : original_speed;
-        std::map<float, float> speed_sections;
-        for (size_t i = 0; i < overhangs_w_speeds.size(); i++) {
-            float distance           = path.width * (1.0 - (overhangs_w_speeds[i].first / 100.0));
-            float speed              = overhangs_w_speeds[i].second.percent ? (speed_base * overhangs_w_speeds[i].second.value / 100.0) :
-                                                                              overhangs_w_speeds[i].second.value;
-            if (speed < EPSILON) speed = speed_base;
-            speed_sections[distance] = speed;
-        }
+                                                 float                      external_perim_reference_speed,
+                                                 float                      default_speed);
 
-        std::map<float, float> fan_speed_sections;
-        for (size_t i = 0; i < overhangs_w_fan_speeds.size(); i++) {
-            float distance           = path.width * (1.0 - (overhangs_w_fan_speeds[i].first / 100.0));
-            float fan_speed            = overhangs_w_fan_speeds[i].second.get_at(extruder_id);
-            fan_speed_sections[distance] = fan_speed;
-        }
-
-        std::vector<ExtendedPoint> extended_points =
-            estimate_points_properties<true, true, true, true>(path.polyline.points, prev_layer_boundaries[current_object], path.width);
-
-        std::vector<ProcessedPoint> processed_points;
-        processed_points.reserve(extended_points.size());
-        for (size_t i = 0; i < extended_points.size(); i++) {
-            const ExtendedPoint &curr = extended_points[i];
-            const ExtendedPoint &next = extended_points[i + 1 < extended_points.size() ? i + 1 : i];
-
-            // The following code artifically increases the distance to provide slowdown for extrusions that are over curled lines
-            float artificial_distance_to_curled_lines = 0.0;
-            const double dist_limit = 10.0 * path.width;
-            {
-                Vec2d middle = 0.5 * (curr.position + next.position);
-                auto line_indices = prev_curled_extrusions[current_object].all_lines_in_radius(Point::new_scale(middle), scale_(dist_limit));
-                if (!line_indices.empty()) {
-                    double len   = (next.position - curr.position).norm();
-                    // For long lines, there is a problem with the additional slowdown. If by accident, there is small curled line near the middle of this long line
-                    //  The whole segment gets slower unnecesarily. For these long lines, we do additional check whether it is worth slowing down.
-                    // NOTE that this is still quite rough approximation, e.g. we are still checking lines only near the middle point
-                    // TODO maybe split the lines into smaller segments before running this alg? but can be demanding, and GCode will be huge
-                    if (len > 8) {
-                        Vec2d dir   = Vec2d(next.position - curr.position) / len;
-                        Vec2d right = Vec2d(-dir.y(), dir.x());
-
-                        Polygon box_of_influence = {
-                            scaled(Vec2d(curr.position + right * dist_limit)),
-                            scaled(Vec2d(next.position + right * dist_limit)),
-                            scaled(Vec2d(next.position - right * dist_limit)),
-                            scaled(Vec2d(curr.position - right * dist_limit)),
-                        };
-
-                        double projected_lengths_sum = 0;
-                        for (size_t idx : line_indices) {
-                            const CurledLine &line   = prev_curled_extrusions[current_object].get_line(idx);
-                            Lines             inside = intersection_ln({{line.a, line.b}}, {box_of_influence});
-                            if (inside.empty())
-                                continue;
-                            double projected_length = abs(dir.dot(unscaled(Vec2d((inside.back().b - inside.back().a).cast<double>()))));
-                            projected_lengths_sum += projected_length;
-                        }
-                        if (projected_lengths_sum < 0.4 * len) {
-                            line_indices.clear();
-                        }
-                    }
-
-                    for (size_t idx : line_indices) {
-                        const CurledLine &line                 = prev_curled_extrusions[current_object].get_line(idx);
-                        float             distance_from_curled = unscaled(line_alg::distance_to(line, Point::new_scale(middle)));
-                        float             dist                 = path.width * (1.0 - (distance_from_curled / dist_limit)) *
-                                     (1.0 - (distance_from_curled / dist_limit)) *
-                                     (line.curled_height / (path.height * 10.0f)); // max_curled_height_factor from SupportSpotGenerator
-                        artificial_distance_to_curled_lines = std::max(artificial_distance_to_curled_lines, dist);
-                    }
-                }
-            }
-
-            auto interpolate_speed = [](const std::map<float, float> &values, float distance) {
-                auto upper_dist = values.lower_bound(distance);
-                if (upper_dist == values.end()) {
-                    return values.rbegin()->second;
-                }
-                if (upper_dist == values.begin()) {
-                    return upper_dist->second;
-                }
-
-                auto  lower_dist = std::prev(upper_dist);
-                float t          = (distance - lower_dist->first) / (upper_dist->first - lower_dist->first);
-                return (1.0f - t) * lower_dist->second + t * upper_dist->second;
-            };
-
-            float extrusion_speed   = std::min(interpolate_speed(speed_sections, curr.distance),
-                                               interpolate_speed(speed_sections, next.distance));
-            float curled_base_speed = interpolate_speed(speed_sections, artificial_distance_to_curled_lines);
-            float final_speed       = std::min(curled_base_speed, extrusion_speed);
-            float fan_speed         = std::min(interpolate_speed(fan_speed_sections, curr.distance),
-                                               interpolate_speed(fan_speed_sections, next.distance));
-
-            processed_points.push_back({scaled(curr.position), final_speed, int(fan_speed)});
-        }
-        return processed_points;
-    }
-};
-
-} // namespace Slic3r
+}} // namespace Slic3r::ExtrusionProcessor
 
 #endif // slic3r_ExtrusionProcessor_hpp_

src/libslic3r/GCode/GCodeProcessor.cpp

@@ -4,8 +4,9 @@
 #include "libslic3r/LocalesUtils.hpp"
 #include "libslic3r/format.hpp"
 #include "libslic3r/I18N.hpp"
-#include "libslic3r/GCodeWriter.hpp"
+#include "libslic3r/GCode/GCodeWriter.hpp"
 #include "libslic3r/I18N.hpp"
+#include "libslic3r/Geometry/ArcWelder.hpp"
 #include "GCodeProcessor.hpp"
 
 #include <boost/algorithm/string/case_conv.hpp>
@@ -43,8 +44,6 @@ static const Slic3r::Vec3f DEFAULT_EXTRUDER_OFFSET = Slic3r::Vec3f::Zero();
 // taken from PrusaResearch.ini - [printer:Original Prusa i3 MK2.5 MMU2]
 static const std::vector<std::string> DEFAULT_EXTRUDER_COLORS = { "#FF8000", "#DB5182", "#3EC0FF", "#FF4F4F", "#FBEB7D" };
 
-static const std::string INTERNAL_G2G3_TAG = "!#!#! internal only - from G2/G3 expansion !#!#!";
-
 namespace Slic3r {
 
 const std::vector<std::string> GCodeProcessor::Reserved_Tags = {
@@ -2363,13 +2362,10 @@ void GCodeProcessor::process_G1(const GCodeReader::GCodeLine& line)
     if (line.has_e()) g1_axes[E] = (double)line.e();
     std::optional<double> g1_feedrate = std::nullopt;
     if (line.has_f()) g1_feedrate = (double)line.f();
-    std::optional<std::string> g1_cmt = std::nullopt;
-    if (!line.comment().empty()) g1_cmt = line.comment();
-
-    process_G1(g1_axes, g1_feedrate, g1_cmt);
+    process_G1(g1_axes, g1_feedrate);
 }
 
-void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes, std::optional<double> feedrate, std::optional<std::string> cmt)
+void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes, std::optional<double> feedrate, G1DiscretizationOrigin origin)
 {
     const float filament_diameter = (static_cast<size_t>(m_extruder_id) < m_result.filament_diameters.size()) ? m_result.filament_diameters[m_extruder_id] : m_result.filament_diameters.back();
     const float filament_radius = 0.5f * filament_diameter;
@@ -2452,7 +2448,7 @@ void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes
             m_height = m_forced_height;
         else if (m_layer_id == 0)
             m_height = m_first_layer_height + m_z_offset;
-        else if (!cmt.has_value() || *cmt != INTERNAL_G2G3_TAG) {
+        else if (origin == G1DiscretizationOrigin::G1) {
             if (m_end_position[Z] > m_extruded_last_z + EPSILON && delta_pos[Z] == 0.0)
                 m_height = m_end_position[Z] - m_extruded_last_z;
         }
@@ -2463,7 +2459,7 @@ void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes
         if (m_end_position[Z] == 0.0f || (m_extrusion_role == GCodeExtrusionRole::Custom && m_layer_id == 0))
             m_end_position[Z] = m_height;
 
-        if (!cmt.has_value() || *cmt != INTERNAL_G2G3_TAG)
+        if (origin == G1DiscretizationOrigin::G1)
             m_extruded_last_z = m_end_position[Z];
         m_options_z_corrector.update(m_height);
 
@@ -2693,18 +2689,48 @@ void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes
     }
 
     // store move
-    store_move_vertex(type, cmt.has_value() && *cmt == INTERNAL_G2G3_TAG);
+    store_move_vertex(type, origin == G1DiscretizationOrigin::G2G3);
 }
 
 void GCodeProcessor::process_G2_G3(const GCodeReader::GCodeLine& line, bool clockwise)
 {
-    if (!line.has('I') || !line.has('J'))
+    enum class EFitting { None, IJ, R };
+    const EFitting fitting = line.has('R') ? EFitting::R : (line.has('I') && line.has('J')) ? EFitting::IJ : EFitting::None;
+
+    if (fitting == EFitting::None)
         return;
 
+    const float filament_diameter = (static_cast<size_t>(m_extruder_id) < m_result.filament_diameters.size()) ? m_result.filament_diameters[m_extruder_id] : m_result.filament_diameters.back();
+    const float filament_radius = 0.5f * filament_diameter;
+    const float area_filament_cross_section = static_cast<float>(M_PI) * sqr(filament_radius);
+
+    AxisCoords end_position = m_start_position;
+    for (unsigned char a = X; a <= E; ++a) {
+        end_position[a] = extract_absolute_position_on_axis((Axis)a, line, double(area_filament_cross_section));
+    }
+
     // relative center
     Vec3f rel_center = Vec3f::Zero();
+#ifndef _NDEBUG
+    double radius = 0.0;
+#endif // _NDEBUG
+    if (fitting == EFitting::R) {
+        float r;
+        if (!line.has_value('R', r) || r == 0.0f)
+            return;
+#ifndef _NDEBUG
+        radius = (double)std::abs(r);
+#endif // _NDEBUG
+        const Vec2f start_pos((float)m_start_position[X], (float)m_start_position[Y]);
+        const Vec2f end_pos((float)end_position[X], (float)end_position[Y]);
+        const Vec2f c = Geometry::ArcWelder::arc_center(start_pos, end_pos, r, !clockwise);
+        rel_center.x() = c.x() - m_start_position[X];
+        rel_center.y() = c.y() - m_start_position[Y];
+    }
+    else {
         if (!line.has_value('I', rel_center.x()) || !line.has_value('J', rel_center.y()))
             return;
+    }
 
     // scale center, if needed
     if (m_units == EUnits::Inches)
@@ -2740,15 +2766,6 @@ void GCodeProcessor::process_G2_G3(const GCodeReader::GCodeLine& line, bool cloc
     // arc center
     arc.center = arc.start + rel_center.cast<double>();
 
-    const float filament_diameter = (static_cast<size_t>(m_extruder_id) < m_result.filament_diameters.size()) ? m_result.filament_diameters[m_extruder_id] : m_result.filament_diameters.back();
-    const float filament_radius = 0.5f * filament_diameter;
-    const float area_filament_cross_section = static_cast<float>(M_PI) * sqr(filament_radius);
-
-    AxisCoords end_position = m_start_position;
-    for (unsigned char a = X; a <= E; ++a) {
-        end_position[a] = extract_absolute_position_on_axis((Axis)a, line, double(area_filament_cross_section));
-    }
-
     // arc end endpoint
     arc.end = Vec3d(end_position[X], end_position[Y], end_position[Z]);
 
@@ -2757,6 +2774,8 @@ void GCodeProcessor::process_G2_G3(const GCodeReader::GCodeLine& line, bool cloc
         // what to do ???
     }
 
+    assert(fitting != EFitting::R || std::abs(radius - arc.start_radius()) < EPSILON);
+
     // updates feedrate from line
     std::optional<float> feedrate;
     if (line.has_f())
@@ -2816,9 +2835,7 @@ void GCodeProcessor::process_G2_G3(const GCodeReader::GCodeLine& line, bool cloc
             g1_feedrate = (double)*feedrate;
         if (extrusion.has_value())
             g1_axes[E] = target[E];
-        std::optional<std::string> g1_cmt = INTERNAL_G2G3_TAG;
-
-        process_G1(g1_axes, g1_feedrate, g1_cmt);
+        process_G1(g1_axes, g1_feedrate, G1DiscretizationOrigin::G2G3);
     };
 
     // calculate arc segments
@@ -2827,8 +2844,13 @@ void GCodeProcessor::process_G2_G3(const GCodeReader::GCodeLine& line, bool cloc
     // https://github.com/prusa3d/Prusa-Firmware/blob/MK3/Firmware/motion_control.cpp
 
     // segments count
+#if 0
     static const double MM_PER_ARC_SEGMENT = 1.0;
     const size_t segments = std::max<size_t>(std::floor(travel_length / MM_PER_ARC_SEGMENT), 1);
+#else
+    static const double gcode_arc_tolerance = 0.0125;
+    const size_t segments = Geometry::ArcWelder::arc_discretization_steps(arc.start_radius(), std::abs(arc.angle), gcode_arc_tolerance);
+#endif
 
     const double inv_segment = 1.0 / double(segments);
     const double theta_per_segment = arc.angle  * inv_segment;

src/libslic3r/GCode/GCodeProcessor.hpp

@@ -56,9 +56,13 @@ namespace Slic3r {
                 time = 0.0f;
                 travel_time = 0.0f;
                 custom_gcode_times.clear();
+                custom_gcode_times.shrink_to_fit();
                 moves_times.clear();
+                moves_times.shrink_to_fit();
                 roles_times.clear();
+                roles_times.shrink_to_fit();
                 layers_times.clear();
+                layers_times.shrink_to_fit();
             }
         };
 
@@ -76,6 +80,7 @@ namespace Slic3r {
                 m.reset();
             }
             volumes_per_color_change.clear();
+            volumes_per_color_change.shrink_to_fit();
             volumes_per_extruder.clear();
             used_filaments_per_role.clear();
             cost_per_extruder.clear();
@@ -680,8 +685,12 @@ namespace Slic3r {
         // Move
         void process_G0(const GCodeReader::GCodeLine& line);
         void process_G1(const GCodeReader::GCodeLine& line);
+        enum class G1DiscretizationOrigin {
+            G1,
+            G2G3,
+        };
         void process_G1(const std::array<std::optional<double>, 4>& axes = { std::nullopt, std::nullopt, std::nullopt, std::nullopt },
-            std::optional<double> feedrate = std::nullopt, std::optional<std::string> cmt = std::nullopt);
+            std::optional<double> feedrate = std::nullopt, G1DiscretizationOrigin origin = G1DiscretizationOrigin::G1);
 
         // Arc Move
         void process_G2_G3(const GCodeReader::GCodeLine& line, bool clockwise);

src/libslic3r/GCode/GCodeWriter.cpp

@@ -1,10 +1,12 @@
 #include "GCodeWriter.hpp"
-#include "CustomGCode.hpp"
+#include "../CustomGCode.hpp"
+
 #include <algorithm>
 #include <iomanip>
 #include <iostream>
 #include <map>
 #include <assert.h>
+#include <string_view>
 
 #ifdef __APPLE__
     #include <boost/spirit/include/karma.hpp>
@@ -13,6 +15,8 @@
 #define FLAVOR_IS(val) this->config.gcode_flavor == val
 #define FLAVOR_IS_NOT(val) this->config.gcode_flavor != val
 
+using namespace std::string_view_literals;
+
 namespace Slic3r {
 
 // static
@@ -90,17 +94,17 @@ std::string GCodeWriter::set_temperature(unsigned int temperature, bool wait, in
     if (wait && (FLAVOR_IS(gcfMakerWare) || FLAVOR_IS(gcfSailfish)))
         return {};
     
-    std::string code, comment;
+    std::string_view code, comment;
     if (wait && FLAVOR_IS_NOT(gcfTeacup) && FLAVOR_IS_NOT(gcfRepRapFirmware)) {
-        code = "M109";
-        comment = "set temperature and wait for it to be reached";
+        code = "M109"sv;
+        comment = "set temperature and wait for it to be reached"sv;
     } else {
         if (FLAVOR_IS(gcfRepRapFirmware)) { // M104 is deprecated on RepRapFirmware
-            code = "G10";
+            code = "G10"sv;
         } else {
-            code = "M104";
+            code = "M104"sv;
         }
-        comment = "set temperature";
+        comment = "set temperature"sv;
     }
     
     std::ostringstream gcode;
@@ -130,22 +134,22 @@ std::string GCodeWriter::set_temperature(unsigned int temperature, bool wait, in
 std::string GCodeWriter::set_bed_temperature(unsigned int temperature, bool wait)
 {
     if (temperature == m_last_bed_temperature && (! wait || m_last_bed_temperature_reached))
-        return std::string();
+        return {};
 
     m_last_bed_temperature = temperature;
     m_last_bed_temperature_reached = wait;
 
-    std::string code, comment;
+    std::string_view code, comment;
     if (wait && FLAVOR_IS_NOT(gcfTeacup)) {
         if (FLAVOR_IS(gcfMakerWare) || FLAVOR_IS(gcfSailfish)) {
-            code = "M109";
+            code = "M109"sv;
         } else {
-            code = "M190";
+            code = "M190"sv;
         }
-        comment = "set bed temperature and wait for it to be reached";
+        comment = "set bed temperature and wait for it to be reached"sv;
     } else {
-        code = "M140";
-        comment = "set bed temperature";
+        code = "M140"sv;
+        comment = "set bed temperature"sv;
     }
     
     std::ostringstream gcode;
@@ -176,7 +180,7 @@ std::string GCodeWriter::set_acceleration_internal(Acceleration type, unsigned i
 
     auto& last_value = separate_travel ? m_last_travel_acceleration : m_last_acceleration ;
     if (acceleration == 0 || acceleration == last_value)
-        return std::string();
+        return {};
     
     last_value = acceleration;
     
@@ -245,7 +249,7 @@ std::string GCodeWriter::toolchange(unsigned int extruder_id)
     return gcode.str();
 }
 
-std::string GCodeWriter::set_speed(double F, const std::string &comment, const std::string &cooling_marker) const
+std::string GCodeWriter::set_speed(double F, const std::string_view comment, const std::string_view cooling_marker) const
 {
     assert(F > 0.);
     assert(F < 100000.);
@@ -257,10 +261,9 @@ std::string GCodeWriter::set_speed(double F, const std::string &comment, const s
     return w.string();
 }
 
-std::string GCodeWriter::travel_to_xy(const Vec2d &point, const std::string &comment)
+std::string GCodeWriter::travel_to_xy(const Vec2d &point, const std::string_view comment)
 {
-    m_pos.x() = point.x();
-    m_pos.y() = point.y();
+    m_pos.head<2>() = point.head<2>();
     
     GCodeG1Formatter w;
     w.emit_xy(point);
@@ -269,7 +272,40 @@ std::string GCodeWriter::travel_to_xy(const Vec2d &point, const std::string &com
     return w.string();
 }
 
-std::string GCodeWriter::travel_to_xyz(const Vec3d &point, const std::string &comment)
+std::string GCodeWriter::travel_to_xy_G2G3IJ(const Vec2d &point, const Vec2d &ij, const bool ccw, const std::string_view comment)
+{
+    assert(std::abs(point.x()) < 1200.);
+    assert(std::abs(point.y()) < 1200.);
+    assert(std::abs(ij.x()) < 1200.);
+    assert(std::abs(ij.y()) < 1200.);
+    assert(std::abs(ij.x()) >= 0.001 || std::abs(ij.y()) >= 0.001);
+ 
+    m_pos.head<2>() = point.head<2>();
+
+    GCodeG2G3Formatter w(ccw);
+    w.emit_xy(point);
+    w.emit_ij(ij);
+    w.emit_comment(this->config.gcode_comments, comment);
+    return w.string();
+}
+
+std::string GCodeWriter::travel_to_xy_G2G3R(const Vec2d &point, const double radius, const bool ccw, const std::string_view comment)
+{
+    assert(std::abs(point.x()) < 1200.);
+    assert(std::abs(point.y()) < 1200.);
+    assert(std::abs(radius) >= 0.001);
+    assert(std::abs(radius) < 1800.);
+
+    m_pos.head<2>() = point.head<2>();
+
+    GCodeG2G3Formatter w(ccw);
+    w.emit_xy(point);
+    w.emit_radius(radius);
+    w.emit_comment(this->config.gcode_comments, comment);
+    return w.string();
+}
+
+std::string GCodeWriter::travel_to_xyz(const Vec3d &point, const std::string_view comment)
 {
     // FIXME: This function was not being used when travel_speed_z was separated (bd6badf).
     // Calculation of feedrate was not updated accordingly. If you want to use
@@ -302,7 +338,7 @@ std::string GCodeWriter::travel_to_xyz(const Vec3d &point, const std::string &co
     return w.string();
 }
 
-std::string GCodeWriter::travel_to_z(double z, const std::string &comment)
+std::string GCodeWriter::travel_to_z(double z, const std::string_view comment)
 {
     /*  If target Z is lower than current Z but higher than nominal Z
         we don't perform the move but we only adjust the nominal Z by
@@ -321,7 +357,7 @@ std::string GCodeWriter::travel_to_z(double z, const std::string &comment)
     return this->_travel_to_z(z, comment);
 }
 
-std::string GCodeWriter::_travel_to_z(double z, const std::string &comment)
+std::string GCodeWriter::_travel_to_z(double z, const std::string_view comment)
 {
     m_pos.z() = z;
 
@@ -348,10 +384,12 @@ bool GCodeWriter::will_move_z(double z) const
     return true;
 }
 
-std::string GCodeWriter::extrude_to_xy(const Vec2d &point, double dE, const std::string &comment)
+std::string GCodeWriter::extrude_to_xy(const Vec2d &point, double dE, const std::string_view comment)
 {
-    m_pos.x() = point.x();
-    m_pos.y() = point.y();
+    assert(dE != 0);
+    assert(std::abs(dE) < 1000.0);
+
+    m_pos.head<2>() = point.head<2>();
 
     GCodeG1Formatter w;
     w.emit_xy(point);
@@ -360,8 +398,47 @@ std::string GCodeWriter::extrude_to_xy(const Vec2d &point, double dE, const std:
     return w.string();
 }
 
+std::string GCodeWriter::extrude_to_xy_G2G3IJ(const Vec2d &point, const Vec2d &ij, const bool ccw, double dE, const std::string_view comment)
+{
+    assert(std::abs(dE) < 1000.0);
+    assert(dE != 0);
+    assert(std::abs(point.x()) < 1200.);
+    assert(std::abs(point.y()) < 1200.);
+    assert(std::abs(ij.x()) < 1200.);
+    assert(std::abs(ij.y()) < 1200.);
+    assert(std::abs(ij.x()) >= 0.001 || std::abs(ij.y()) >= 0.001);
+
+    m_pos.head<2>() = point.head<2>();
+
+    GCodeG2G3Formatter w(ccw);
+    w.emit_xy(point);
+    w.emit_ij(ij);
+    w.emit_e(m_extrusion_axis, m_extruder->extrude(dE).second);
+    w.emit_comment(this->config.gcode_comments, comment);
+    return w.string();
+}
+
+std::string GCodeWriter::extrude_to_xy_G2G3R(const Vec2d &point, const double radius, const bool ccw, double dE, const std::string_view comment)
+{
+    assert(dE != 0);
+    assert(std::abs(dE) < 1000.0);
+    assert(std::abs(point.x()) < 1200.);
+    assert(std::abs(point.y()) < 1200.);
+    assert(std::abs(radius) >= 0.001);
+    assert(std::abs(radius) < 1800.);
+
+    m_pos.head<2>() = point.head<2>();
+
+    GCodeG2G3Formatter w(ccw);
+    w.emit_xy(point);
+    w.emit_radius(radius);
+    w.emit_e(m_extrusion_axis, m_extruder->extrude(dE).second);
+    w.emit_comment(this->config.gcode_comments, comment);
+    return w.string();
+}
+
 #if 0
-std::string GCodeWriter::extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment)
+std::string GCodeWriter::extrude_to_xyz(const Vec3d &point, double dE, const std::string_view comment)
 {
     m_pos = point;
     m_lifted = 0;
@@ -397,8 +474,11 @@ std::string GCodeWriter::retract_for_toolchange(bool before_wipe)
     );
 }
 
-std::string GCodeWriter::_retract(double length, double restart_extra, const std::string &comment)
+std::string GCodeWriter::_retract(double length, double restart_extra, const std::string_view comment)
 {
+    assert(std::abs(length) < 1000.0);
+    assert(std::abs(restart_extra) < 1000.0);
+
     /*  If firmware retraction is enabled, we use a fake value of 1
         since we ignore the actual configured retract_length which 
         might be 0, in which case the retraction logic gets skipped. */

src/libslic3r/GCode/GCodeWriter.hpp

@@ -1,13 +1,15 @@
 #ifndef slic3r_GCodeWriter_hpp_
 #define slic3r_GCodeWriter_hpp_
 
-#include "libslic3r.h"
+#include "../libslic3r.h"
+#include "../Extruder.hpp"
+#include "../Point.hpp"
+#include "../PrintConfig.hpp"
+#include "CoolingBuffer.hpp"
+
 #include <string>
+#include <string_view>
 #include <charconv>
-#include "Extruder.hpp"
-#include "Point.hpp"
-#include "PrintConfig.hpp"
-#include "GCode/CoolingBuffer.hpp"
 
 namespace Slic3r {
 
@@ -56,13 +58,17 @@ public:
     // printed with the same extruder.
     std::string toolchange_prefix() const;
     std::string toolchange(unsigned int extruder_id);
-    std::string set_speed(double F, const std::string &comment = std::string(), const std::string &cooling_marker = std::string()) const;
-    std::string travel_to_xy(const Vec2d &point, const std::string &comment = std::string());
-    std::string travel_to_xyz(const Vec3d &point, const std::string &comment = std::string());
-    std::string travel_to_z(double z, const std::string &comment = std::string());
+    std::string set_speed(double F, const std::string_view comment = {}, const std::string_view cooling_marker = {}) const;
+    std::string travel_to_xy(const Vec2d &point, const std::string_view comment = {});
+    std::string travel_to_xy_G2G3IJ(const Vec2d &point, const Vec2d &ij, const bool ccw, const std::string_view comment = {});
+    std::string travel_to_xy_G2G3R(const Vec2d &point, const double radius, const bool ccw, const std::string_view comment = {});
+    std::string travel_to_xyz(const Vec3d &point, const std::string_view comment = {});
+    std::string travel_to_z(double z, const std::string_view comment = {});
     bool        will_move_z(double z) const;
-    std::string extrude_to_xy(const Vec2d &point, double dE, const std::string &comment = std::string());
-//    std::string extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment = std::string());
+    std::string extrude_to_xy(const Vec2d &point, double dE, const std::string_view comment = {});
+    std::string extrude_to_xy_G2G3IJ(const Vec2d &point, const Vec2d &ij, const bool ccw, double dE, const std::string_view comment);
+    std::string extrude_to_xy_G2G3R(const Vec2d &point, const double radius, const bool ccw, double dE, const std::string_view comment);
+//    std::string extrude_to_xyz(const Vec3d &point, double dE, const std::string_view comment = {});
     std::string retract(bool before_wipe = false);
     std::string retract_for_toolchange(bool before_wipe = false);
     std::string unretract();
@@ -113,8 +119,8 @@ private:
         Print
     };
 
-    std::string _travel_to_z(double z, const std::string &comment);
-    std::string _retract(double length, double restart_extra, const std::string &comment);
+    std::string _travel_to_z(double z, const std::string_view comment);
+    std::string _retract(double length, double restart_extra, const std::string_view comment);
     std::string set_acceleration_internal(Acceleration type, unsigned int acceleration);
 };
 
@@ -152,6 +158,10 @@ public:
     static double                                 quantize(double v, size_t ndigits) { return std::round(v * pow_10[ndigits]) * pow_10_inv[ndigits]; }
     static double                                 quantize_xyzf(double v) { return quantize(v, XYZF_EXPORT_DIGITS); }
     static double                                 quantize_e(double v) { return quantize(v, E_EXPORT_DIGITS); }
+    static Vec2d                                  quantize(const Vec2d &pt)
+        { return { quantize(pt.x(), XYZF_EXPORT_DIGITS), quantize(pt.y(), XYZF_EXPORT_DIGITS) }; }
+    static Vec3d                                  quantize(const Vec3d &pt)
+        { return { quantize(pt.x(), XYZF_EXPORT_DIGITS), quantize(pt.y(), XYZF_EXPORT_DIGITS), quantize(pt.z(), XYZF_EXPORT_DIGITS) }; }
 
     void emit_axis(const char axis, const double v, size_t digits);
 
@@ -170,7 +180,20 @@ public:
         this->emit_axis('Z', z, XYZF_EXPORT_DIGITS);
     }
 
-    void emit_e(const std::string &axis, double v) {
+    void emit_ij(const Vec2d &point) {
+        if (point.x() != 0)
+            this->emit_axis('I', point.x(), XYZF_EXPORT_DIGITS);
+        if (point.y() != 0)
+            this->emit_axis('J', point.y(), XYZF_EXPORT_DIGITS);
+    }
+
+    // Positive radius means a smaller arc, 
+    // negative radius means a larger arc.
+    void emit_radius(const double radius) {
+        this->emit_axis('R', radius, XYZF_EXPORT_DIGITS);
+    }
+
+    void emit_e(const std::string_view axis, double v) {
         if (! axis.empty()) {
             // not gcfNoExtrusion
             this->emit_axis(axis[0], v, E_EXPORT_DIGITS);
@@ -181,12 +204,12 @@ public:
         this->emit_axis('F', speed, XYZF_EXPORT_DIGITS);
     }
 
-    void emit_string(const std::string &s) {
-        strncpy(ptr_err.ptr, s.c_str(), s.size());
+    void emit_string(const std::string_view s) {
+        strncpy(ptr_err.ptr, s.data(), s.size());
         ptr_err.ptr += s.size();
     }
 
-    void emit_comment(bool allow_comments, const std::string &comment) {
+    void emit_comment(bool allow_comments, const std::string_view comment) {
         if (allow_comments && ! comment.empty()) {
             *ptr_err.ptr ++ = ' '; *ptr_err.ptr ++ = ';'; *ptr_err.ptr ++ = ' ';
             this->emit_string(comment);
@@ -210,14 +233,25 @@ public:
     GCodeG1Formatter() {
         this->buf[0] = 'G';
         this->buf[1] = '1';
-        this->buf_end = buf + buflen;
-        this->ptr_err.ptr = this->buf + 2;
+        this->ptr_err.ptr += 2;
     }
 
     GCodeG1Formatter(const GCodeG1Formatter&) = delete;
     GCodeG1Formatter& operator=(const GCodeG1Formatter&) = delete;
 };
 
+class GCodeG2G3Formatter : public GCodeFormatter {
+public:
+    GCodeG2G3Formatter(bool ccw) {
+        this->buf[0] = 'G';
+        this->buf[1] = ccw ? '3' : '2';
+        this->ptr_err.ptr += 2;
+    }
+
+    GCodeG2G3Formatter(const GCodeG2G3Formatter&) = delete;
+    GCodeG2G3Formatter& operator=(const GCodeG2G3Formatter&) = delete;
+};
+
 } /* namespace Slic3r */
 
 #endif /* slic3r_GCodeWriter_hpp_ */

src/libslic3r/GCode/PrintExtents.cpp

@@ -30,7 +30,7 @@ static inline BoundingBox extrusion_polyline_extents(const Polyline &polyline, c
 
 static inline BoundingBoxf extrusionentity_extents(const ExtrusionPath &extrusion_path)
 {
-    BoundingBox bbox = extrusion_polyline_extents(extrusion_path.polyline, coord_t(scale_(0.5 * extrusion_path.width)));
+    BoundingBox bbox = extrusion_polyline_extents(extrusion_path.polyline, coord_t(scale_(0.5 * extrusion_path.width())));
     BoundingBoxf bboxf;
     if (! empty(bbox)) {
         bboxf.min = unscale(bbox.min);
@@ -44,7 +44,7 @@ static inline BoundingBoxf extrusionentity_extents(const ExtrusionLoop &extrusio
 {
     BoundingBox bbox;
     for (const ExtrusionPath &extrusion_path : extrusion_loop.paths)
-        bbox.merge(extrusion_polyline_extents(extrusion_path.polyline, coord_t(scale_(0.5 * extrusion_path.width))));
+        bbox.merge(extrusion_polyline_extents(extrusion_path.polyline, coord_t(scale_(0.5 * extrusion_path.width()))));
     BoundingBoxf bboxf;
     if (! empty(bbox)) {
         bboxf.min = unscale(bbox.min);
@@ -58,7 +58,7 @@ static inline BoundingBoxf extrusionentity_extents(const ExtrusionMultiPath &ext
 {
     BoundingBox bbox;
     for (const ExtrusionPath &extrusion_path : extrusion_multi_path.paths)
-        bbox.merge(extrusion_polyline_extents(extrusion_path.polyline, coord_t(scale_(0.5 * extrusion_path.width))));
+        bbox.merge(extrusion_polyline_extents(extrusion_path.polyline, coord_t(scale_(0.5 * extrusion_path.width()))));
     BoundingBoxf bboxf;
     if (! empty(bbox)) {
         bboxf.min = unscale(bbox.min);

src/libslic3r/GCode/SeamPlacer.cpp

@@ -1484,7 +1484,7 @@ void SeamPlacer::init(const Print &print, std::function<void(void)> throw_if_can
     }
 }
 
-void SeamPlacer::place_seam(const Layer *layer, ExtrusionLoop &loop, bool external_first,
+Point SeamPlacer::place_seam(const Layer *layer, const ExtrusionLoop &loop, bool external_first,
         const Point &last_pos) const {
     using namespace SeamPlacerImpl;
     const PrintObject *po = layer->object();
@@ -1587,7 +1587,7 @@ void SeamPlacer::place_seam(const Layer *layer, ExtrusionLoop &loop, bool extern
         //lastly, for internal perimeters, do the staggering if requested
         if (po->config().staggered_inner_seams && loop.length() > 0.0) {
             //fix depth, it is sometimes strongly underestimated
-            depth = std::max(loop.paths[projected_point.path_idx].width, depth);
+            depth = std::max(loop.paths[projected_point.path_idx].width(), depth);
 
             while (depth > 0.0f) {
                 auto next_point = get_next_loop_point(projected_point);
@@ -1605,14 +1605,7 @@ void SeamPlacer::place_seam(const Layer *layer, ExtrusionLoop &loop, bool extern
         }
     }
 
-    // Because the G-code export has 1um resolution, don't generate segments shorter than 1.5 microns,
-    // thus empty path segments will not be produced by G-code export.
-    if (!loop.split_at_vertex(seam_point, scaled<double>(0.0015))) {
-        // The point is not in the original loop.
-        // Insert it.
-        loop.split_at(seam_point, true);
-    }
-
+    return seam_point;
 }
 
 } // namespace Slic3r

src/libslic3r/GCode/SeamPlacer.hpp

@@ -141,7 +141,7 @@ public:
 
     void init(const Print &print, std::function<void(void)> throw_if_canceled_func);
 
-    void place_seam(const Layer *layer, ExtrusionLoop &loop, bool external_first, const Point &last_pos) const;
+    Point place_seam(const Layer *layer, const ExtrusionLoop &loop, bool external_first, const Point &last_pos) const;
 
 private:
     void gather_seam_candidates(const PrintObject *po, const SeamPlacerImpl::GlobalModelInfo &global_model_info);

src/libslic3r/GCode/SmoothPath.cpp

@@ -0,0 +1,257 @@
+#include "SmoothPath.hpp"
+
+#include "../ExtrusionEntity.hpp"
+#include "../ExtrusionEntityCollection.hpp"
+
+namespace Slic3r::GCode {
+
+// Length of a smooth path.
+double length(const SmoothPath &path)
+{
+    double l = 0;
+    for (const SmoothPathElement &el : path)
+        l += Geometry::ArcWelder::path_length<double>(el.path);
+    return l;
+}
+
+// Returns true if the smooth path is longer than a threshold.
+bool longer_than(const SmoothPath &path, double length)
+{
+    for (const SmoothPathElement &el : path) {
+        for (auto it = std::next(el.path.begin()); it != el.path.end(); ++ it) {
+            length -= Geometry::ArcWelder::segment_length<double>(*std::prev(it), *it);
+            if (length < 0)
+                return true;
+        }
+    }
+    return length < 0;
+}
+
+std::optional<Point> sample_path_point_at_distance_from_start(const SmoothPath &path, double distance)
+{
+    if (distance >= 0) {
+        for (const SmoothPathElement &el : path) {
+            auto it  = el.path.begin();
+            auto end = el.path.end();
+            Point prev_point = it->point;
+            for (++ it; it != end; ++ it) {
+                Point point = it->point;
+                if (it->linear()) {
+                    // Linear segment
+                    Vec2d  v    = (point - prev_point).cast<double>();
+                    double lsqr = v.squaredNorm();
+                    if (lsqr > sqr(distance))
+                        return std::make_optional<Point>(prev_point + (v * (distance / sqrt(lsqr))).cast<coord_t>());
+                    distance -= sqrt(lsqr);
+                } else {
+                    // Circular segment
+                    float angle = Geometry::ArcWelder::arc_angle(prev_point.cast<float>(), point.cast<float>(), it->radius);
+                    double len = std::abs(it->radius) * angle;
+                    if (len > distance) {
+                        // Rotate the segment end point in reverse towards the start point.
+                        return std::make_optional<Point>(prev_point.rotated(- angle * (distance / len),
+                            Geometry::ArcWelder::arc_center(prev_point.cast<float>(), point.cast<float>(), it->radius, it->ccw()).cast<coord_t>()));
+                    }
+                    distance -= len;
+                }
+                if (distance < 0)
+                    return std::make_optional<Point>(point);
+                prev_point = point;
+            }
+        }
+    }
+    // Failed.
+    return {};
+}
+
+std::optional<Point> sample_path_point_at_distance_from_end(const SmoothPath &path, double distance)
+{
+    if (distance >= 0) {
+        for (const SmoothPathElement& el : path) {
+            auto it = el.path.begin();
+            auto end = el.path.end();
+            Point prev_point = it->point;
+            for (++it; it != end; ++it) {
+                Point point = it->point;
+                if (it->linear()) {
+                    // Linear segment
+                    Vec2d  v = (point - prev_point).cast<double>();
+                    double lsqr = v.squaredNorm();
+                    if (lsqr > sqr(distance))
+                        return std::make_optional<Point>(prev_point + (v * (distance / sqrt(lsqr))).cast<coord_t>());
+                    distance -= sqrt(lsqr);
+                }
+                else {
+                    // Circular segment
+                    float angle = Geometry::ArcWelder::arc_angle(prev_point.cast<float>(), point.cast<float>(), it->radius);
+                    double len = std::abs(it->radius) * angle;
+                    if (len > distance) {
+                        // Rotate the segment end point in reverse towards the start point.
+                        return std::make_optional<Point>(prev_point.rotated(-angle * (distance / len),
+                            Geometry::ArcWelder::arc_center(prev_point.cast<float>(), point.cast<float>(), it->radius, it->ccw()).cast<coord_t>()));
+                    }
+                    distance -= len;
+                }
+                if (distance < 0)
+                    return std::make_optional<Point>(point);
+                prev_point = point;
+            }
+        }
+    }
+    // Failed.
+    return {};
+}
+
+double clip_end(SmoothPath &path, double distance)
+{
+    while (! path.empty() && distance > 0) {
+        Geometry::ArcWelder::Path &p = path.back().path;
+        distance = clip_end(p, distance);
+        if (p.empty()) {
+            path.pop_back();
+        } else {
+            // Trailing path was trimmed and it is valid.
+            assert(path.back().path.size() > 1);
+            assert(distance == 0);
+            // Distance to go is zero.
+            return 0;
+        }
+    }
+    // Return distance to go after the whole smooth path was trimmed to zero.
+    return distance;
+}
+
+void SmoothPathCache::interpolate_add(const ExtrusionPath &path, const InterpolationParameters &params)
+{
+    double tolerance = params.tolerance;
+    if (path.role().is_sparse_infill())
+        // Use 3x lower resolution than the object fine detail for sparse infill.
+        tolerance *= 3.;
+    else if (path.role().is_support())
+        // Use 4x lower resolution than the object fine detail for support.
+        tolerance *= 4.;
+    else if (path.role().is_skirt())
+        // Brim is currently marked as skirt.
+        // Use 4x lower resolution than the object fine detail for skirt & brim.
+        tolerance *= 4.;
+    m_cache[&path.polyline] = Slic3r::Geometry::ArcWelder::fit_path(path.polyline.points, tolerance, params.fit_circle_tolerance);
+}
+
+void SmoothPathCache::interpolate_add(const ExtrusionMultiPath &multi_path, const InterpolationParameters &params)
+{
+    for (const ExtrusionPath &path : multi_path.paths)
+        this->interpolate_add(path, params);
+}
+
+void SmoothPathCache::interpolate_add(const ExtrusionLoop &loop, const InterpolationParameters &params)
+{
+    for (const ExtrusionPath &path : loop.paths)
+        this->interpolate_add(path, params);
+}
+
+void SmoothPathCache::interpolate_add(const ExtrusionEntityCollection &eec, const InterpolationParameters &params)
+{
+    for (const ExtrusionEntity *ee : eec) {
+        if (ee->is_collection())
+            this->interpolate_add(*static_cast<const ExtrusionEntityCollection*>(ee), params);
+        else if (const ExtrusionPath *path = dynamic_cast<const ExtrusionPath*>(ee); path)
+            this->interpolate_add(*path, params);
+        else if (const ExtrusionMultiPath *multi_path = dynamic_cast<const ExtrusionMultiPath*>(ee); multi_path)
+            this->interpolate_add(*multi_path, params);
+        else if (const ExtrusionLoop *loop = dynamic_cast<const ExtrusionLoop*>(ee); loop)
+            this->interpolate_add(*loop, params);
+        else
+            assert(false);
+    }
+}
+
+const Geometry::ArcWelder::Path* SmoothPathCache::resolve(const Polyline *pl) const
+{
+    auto it = m_cache.find(pl);
+    return it == m_cache.end() ? nullptr : &it->second;
+}
+
+const Geometry::ArcWelder::Path* SmoothPathCache::resolve(const ExtrusionPath &path) const
+{
+    return this->resolve(&path.polyline);
+}
+
+Geometry::ArcWelder::Path SmoothPathCache::resolve_or_fit(const ExtrusionPath &path, bool reverse, double tolerance) const
+{
+    Geometry::ArcWelder::Path out;
+    if (const Geometry::ArcWelder::Path *cached = this->resolve(path); cached)
+        out = *cached;
+    else
+        out = Geometry::ArcWelder::fit_polyline(path.polyline.points, tolerance);
+    if (reverse)
+        Geometry::ArcWelder::reverse(out);
+    return out;
+}
+
+SmoothPath SmoothPathCache::resolve_or_fit(const ExtrusionPaths &paths, bool reverse, double resolution) const
+{
+    SmoothPath out;
+    out.reserve(paths.size());
+    if (reverse) {
+        for (auto it = paths.crbegin(); it != paths.crend(); ++ it)
+            out.push_back({ it->attributes(), this->resolve_or_fit(*it, true, resolution) });
+    } else {
+        for (auto it = paths.cbegin(); it != paths.cend(); ++ it)
+            out.push_back({ it->attributes(), this->resolve_or_fit(*it, false, resolution) });
+    }
+    return out;
+}
+
+SmoothPath SmoothPathCache::resolve_or_fit(const ExtrusionMultiPath &multipath, bool reverse, double resolution) const
+{
+    return this->resolve_or_fit(multipath.paths, reverse, resolution);
+}
+
+SmoothPath SmoothPathCache::resolve_or_fit_split_with_seam(
+    const ExtrusionLoop &loop, const bool reverse, const double resolution,
+    const Point &seam_point, const double seam_point_merge_distance_threshold) const
+{
+    SmoothPath out = this->resolve_or_fit(loop.paths, reverse, resolution);
+    assert(! out.empty());
+    if (! out.empty()) {
+        // Find a closest point on a vector of smooth paths.
+        Geometry::ArcWelder::PathSegmentProjection proj;
+        int                                        proj_path = -1;
+        for (const SmoothPathElement &el : out)
+            if (Geometry::ArcWelder::PathSegmentProjection this_proj = Geometry::ArcWelder::point_to_path_projection(el.path, seam_point, proj.distance2);
+                this_proj.valid()) {
+                // Found a better (closer) projection.
+                assert(this_proj.distance2 < proj.distance2);
+                assert(this_proj.segment_id >= 0 && this_proj.segment_id < el.path.size());
+                proj = this_proj;
+                proj_path = &el - out.data();
+                if (proj.distance2 == 0)
+                    // There will be no better split point found than one with zero distance.
+                    break;
+            }
+        assert(proj_path >= 0);
+        // Split the path at the closest point.
+        Geometry::ArcWelder::Path &path = out[proj_path].path;
+        std::pair<Geometry::ArcWelder::Path, Geometry::ArcWelder::Path> split = Geometry::ArcWelder::split_at(
+            path, proj, seam_point_merge_distance_threshold);
+        if (split.second.empty()) {
+            std::rotate(out.begin(), out.begin() + proj_path + 1, out.end());
+            assert(out.back().path == split.first);
+        } else {
+            ExtrusionAttributes attr = out[proj_path].path_attributes;
+            std::rotate(out.begin(), out.begin() + proj_path, out.end());
+            out.front().path = std::move(split.second);
+            if (! split.first.empty()) {
+                if (out.back().path_attributes == attr) {
+                    // Merge with the last segment.
+                    out.back().path.insert(out.back().path.end(), std::next(split.first.begin()), split.first.end());
+                } else
+                    out.push_back({ attr, std::move(split.first) });
+            }
+        }
+    }
+
+    return out;
+}
+
+} // namespace Slic3r::GCode

src/libslic3r/GCode/SmoothPath.hpp

@@ -0,0 +1,87 @@
+#ifndef slic3r_GCode_SmoothPath_hpp_
+#define slic3r_GCode_SmoothPath_hpp_
+
+#include <ankerl/unordered_dense.h>
+
+#include "../ExtrusionEntity.hpp"
+#include "../Geometry/ArcWelder.hpp"
+
+namespace Slic3r {
+
+class ExtrusionEntityCollection;
+
+namespace GCode {
+
+struct SmoothPathElement
+{
+    ExtrusionAttributes         path_attributes;
+    Geometry::ArcWelder::Path   path;
+};
+
+using SmoothPath = std::vector<SmoothPathElement>;
+
+// Length of a smooth path.
+double length(const SmoothPath &path);
+// Returns true if the smooth path is longer than a threshold.
+bool longer_than(const SmoothPath &path, const double length);
+
+std::optional<Point> sample_path_point_at_distance_from_start(const SmoothPath &path, double distance);
+std::optional<Point> sample_path_point_at_distance_from_end(const SmoothPath &path, double distance);
+
+// Clip end of a smooth path, for seam hiding.
+double clip_end(SmoothPath &path, double distance);
+
+class SmoothPathCache
+{
+public:
+    struct InterpolationParameters {
+        double tolerance;
+        double fit_circle_tolerance;
+    };
+
+    void interpolate_add(const ExtrusionPath             &ee,  const InterpolationParameters &params);
+    void interpolate_add(const ExtrusionMultiPath        &ee,  const InterpolationParameters &params);
+    void interpolate_add(const ExtrusionLoop             &ee,  const InterpolationParameters &params);
+    void interpolate_add(const ExtrusionEntityCollection &eec, const InterpolationParameters &params);
+
+    const Geometry::ArcWelder::Path* resolve(const Polyline      *pl) const;
+    const Geometry::ArcWelder::Path* resolve(const ExtrusionPath &path) const;
+
+    // Look-up a smooth representation of path in the cache. If it does not exist, produce a simplified polyline.
+    Geometry::ArcWelder::Path        resolve_or_fit(const ExtrusionPath &path, bool reverse, double resolution) const;
+
+    // Look-up a smooth representation of path in the cache. If it does not exist, produce a simplified polyline.
+    SmoothPath                       resolve_or_fit(const ExtrusionPaths &paths, bool reverse, double resolution) const;
+    SmoothPath                       resolve_or_fit(const ExtrusionMultiPath &path, bool reverse, double resolution) const;
+
+    // Look-up a smooth representation of path in the cache. If it does not exist, produce a simplified polyline.
+    SmoothPath                       resolve_or_fit_split_with_seam(
+        const ExtrusionLoop &path, const bool reverse, const double resolution,
+        const Point &seam_point, const double seam_point_merge_distance_threshold) const;
+
+private:
+    ankerl::unordered_dense::map<const Polyline*, Geometry::ArcWelder::Path>    m_cache;
+};
+
+// Encapsulates references to global and layer local caches of smooth extrusion paths.
+class SmoothPathCaches final
+{
+public:
+    SmoothPathCaches() = delete;
+    SmoothPathCaches(const SmoothPathCache &global, const SmoothPathCache &layer_local) : 
+        m_global(&global), m_layer_local(&layer_local) {}
+    SmoothPathCaches operator=(const SmoothPathCaches &rhs)
+        { m_global = rhs.m_global; m_layer_local = rhs.m_layer_local; return *this; }
+
+    const SmoothPathCache& global() const { return *m_global; }
+    const SmoothPathCache& layer_local() const { return *m_layer_local; }
+
+private:
+    const SmoothPathCache *m_global;
+    const SmoothPathCache *m_layer_local;
+};
+
+} // namespace GCode
+} // namespace Slic3r
+
+#endif // slic3r_GCode_SmoothPath_hpp_

src/libslic3r/GCode/Wipe.cpp

@@ -0,0 +1,252 @@
+#include "Wipe.hpp"
+#include "../GCode.hpp"
+
+#include <string_view>
+
+#include <Eigen/Geometry>
+
+using namespace std::string_view_literals;
+
+namespace Slic3r::GCode {
+
+void Wipe::init(const PrintConfig &config, const std::vector<unsigned int> &extruders)
+{
+    this->reset_path();
+
+    // Calculate maximum wipe length to accumulate by the wipe cache.
+    // Paths longer than wipe_xy should never be needed for the wipe move.
+    double wipe_xy = 0;
+    const bool multimaterial = extruders.size() > 1;
+    for (auto id : extruders)
+        if (config.wipe.get_at(id)) {
+            // Wipe length to extrusion ratio.
+            const double xy_to_e = this->calc_xy_to_e_ratio(config, id);
+            wipe_xy = std::max(wipe_xy, xy_to_e * config.retract_length.get_at(id));
+            if (multimaterial)
+                wipe_xy = std::max(wipe_xy, xy_to_e * config.retract_length_toolchange.get_at(id));
+        }
+
+    if (wipe_xy == 0)
+        this->disable();
+    else
+        this->enable(wipe_xy);
+}
+
+void Wipe::set_path(SmoothPath &&path, bool reversed)
+{
+    this->reset_path();
+
+    if (this->enabled() && ! path.empty()) {
+        if (reversed) {
+            m_path = std::move(path.back().path);
+            Geometry::ArcWelder::reverse(m_path);
+            int64_t len = Geometry::ArcWelder::estimate_path_length(m_path);
+            for (auto it = std::next(path.rbegin()); len < m_wipe_len_max && it != path.rend(); ++ it) {
+                if (it->path_attributes.role.is_bridge())
+                    break; // Do not perform a wipe on bridges.
+                assert(it->path.size() >= 2);
+                assert(m_path.back().point == it->path.back().point);
+                if (m_path.back().point != it->path.back().point)
+                    // ExtrusionMultiPath is interrupted in some place. This should not really happen.
+                    break;
+                len += Geometry::ArcWelder::estimate_path_length(it->path);
+                m_path.insert(m_path.end(), it->path.rbegin() + 1, it->path.rend());
+            }
+        } else {
+            m_path = std::move(path.front().path);
+            int64_t len = Geometry::ArcWelder::estimate_path_length(m_path);
+            for (auto it = std::next(path.begin()); len < m_wipe_len_max && it != path.end(); ++ it) {
+                if (it->path_attributes.role.is_bridge())
+                    break; // Do not perform a wipe on bridges.
+                assert(it->path.size() >= 2);
+                assert(m_path.back().point == it->path.front().point);
+                if (m_path.back().point != it->path.front().point)
+                    // ExtrusionMultiPath is interrupted in some place. This should not really happen.
+                    break;
+                len += Geometry::ArcWelder::estimate_path_length(it->path);
+                m_path.insert(m_path.end(), it->path.begin() + 1, it->path.end());
+            }
+        }
+    }
+
+    assert(m_path.empty() || m_path.size() > 1);
+}
+
+std::string Wipe::wipe(GCodeGenerator &gcodegen, bool toolchange)
+{
+    std::string     gcode;
+    const Extruder &extruder = *gcodegen.writer().extruder();
+    static constexpr const std::string_view wipe_retract_comment = "wipe and retract"sv;
+
+    // Remaining quantized retraction length.
+    if (double retract_length = extruder.retract_to_go(toolchange ? extruder.retract_length_toolchange() : extruder.retract_length()); 
+        retract_length > 0 && this->has_path()) {
+        // Delayed emitting of a wipe start tag.
+        bool wiped = false;
+        const double wipe_speed = this->calc_wipe_speed(gcodegen.writer().config);
+        auto start_wipe = [&wiped, &gcode, &gcodegen, wipe_speed](){
+            if (! wiped) {
+                wiped = true;
+                gcode += ";" + GCodeProcessor::reserved_tag(GCodeProcessor::ETags::Wipe_Start) + "\n";
+                gcode += gcodegen.writer().set_speed(wipe_speed * 60, {}, gcodegen.enable_cooling_markers() ? ";_WIPE"sv : ""sv);
+            }
+        };
+        const double xy_to_e    = this->calc_xy_to_e_ratio(gcodegen.writer().config, extruder.id());
+        auto         wipe_linear = [&gcode, &gcodegen, &retract_length, xy_to_e](const Vec2d &prev_quantized, Vec2d &p) {
+            Vec2d  p_quantized = GCodeFormatter::quantize(p);
+            if (p_quantized == prev_quantized) {
+                p = p_quantized;
+                return false;
+            }
+            double segment_length = (p_quantized - prev_quantized).norm();
+            // Quantize E axis as it is to be extruded as a whole segment.
+            double dE = GCodeFormatter::quantize_e(xy_to_e * segment_length);
+            bool   done = false;
+            if (dE > retract_length - EPSILON) {
+                if (dE > retract_length + EPSILON)
+                    // Shorten the segment.
+                    p = GCodeFormatter::quantize(Vec2d(prev_quantized + (p - prev_quantized) * (retract_length / dE)));
+                else
+                    p = p_quantized;
+                dE   = retract_length;
+                done = true;
+            } else
+                p = p_quantized;
+            gcode += gcodegen.writer().extrude_to_xy(p, -dE, wipe_retract_comment);
+            retract_length -= dE;
+            return done;
+        };
+        const bool emit_radius = gcodegen.config().arc_fitting == ArcFittingType::EmitRadius;
+        auto         wipe_arc = [&gcode, &gcodegen, &retract_length, xy_to_e, emit_radius](
+            const Vec2d &prev_quantized, Vec2d &p, double radius_in, const bool ccw) {
+            Vec2d  p_quantized = GCodeFormatter::quantize(p);
+            if (p_quantized == prev_quantized) {
+                p = p_quantized;
+                return false;
+            }
+            // Only quantize radius if emitting it directly into G-code. Otherwise use the exact radius for calculating the IJ values.
+            double radius = emit_radius ? GCodeFormatter::quantize_xyzf(radius_in) : radius_in;
+            Vec2d  center = Geometry::ArcWelder::arc_center(prev_quantized.cast<double>(), p_quantized.cast<double>(), double(radius), ccw);
+            float  angle  = Geometry::ArcWelder::arc_angle(prev_quantized.cast<double>(), p_quantized.cast<double>(), double(radius));
+            assert(angle > 0);
+            double segment_length = angle * std::abs(radius);
+            double dE = GCodeFormatter::quantize_e(xy_to_e * segment_length);
+            bool   done = false;
+            if (dE > retract_length - EPSILON) {
+                if (dE > retract_length + EPSILON) {
+                    // Shorten the segment. Recalculate the arc from the unquantized end coordinate.
+                    center = Geometry::ArcWelder::arc_center(prev_quantized.cast<double>(), p.cast<double>(), double(radius), ccw);
+                    angle = Geometry::ArcWelder::arc_angle(prev_quantized.cast<double>(), p.cast<double>(), double(radius));
+                    segment_length = angle * std::abs(radius);
+                    dE = xy_to_e * segment_length;
+                    p = GCodeFormatter::quantize(
+                            Vec2d(center + Eigen::Rotation2D((ccw ? angle : -angle) * (retract_length / dE)) * (prev_quantized - center)));
+                } else
+                    p = p_quantized;
+                dE   = retract_length;
+                done = true;
+            } else
+                p = p_quantized;
+            assert(dE > 0);
+            if (emit_radius) {
+                gcode += gcodegen.writer().extrude_to_xy_G2G3R(p, radius, ccw, -dE, wipe_retract_comment);
+            } else {
+                // Calculate quantized IJ circle center offset.
+                gcode += gcodegen.writer().extrude_to_xy_G2G3IJ(
+                    p, GCodeFormatter::quantize(Vec2d(center - prev_quantized)), ccw, -dE, wipe_retract_comment);
+            }
+            retract_length -= dE;
+            return done;
+        };
+        // Start with the current position, which may be different from the wipe path start in case of loop clipping.
+        Vec2d prev = gcodegen.point_to_gcode_quantized(gcodegen.last_pos());
+        auto  it   = this->path().begin();
+        Vec2d p    = gcodegen.point_to_gcode(it->point + m_offset);
+        ++ it;
+        bool done = false;
+        if (p != prev) {
+            start_wipe();
+            done = wipe_linear(prev, p);
+        }
+        if (! done) {
+            prev = p;
+            auto end = this->path().end();
+            for (; it != end && ! done; ++ it) {
+                p = gcodegen.point_to_gcode(it->point + m_offset);
+                if (p != prev) {
+                    start_wipe();
+                    if (it->linear() ?
+                        wipe_linear(prev, p) :
+                        wipe_arc(prev, p, unscaled<double>(it->radius), it->ccw()))
+                        break;
+                    prev = p;
+                }
+            }
+        }
+        if (wiped) {
+            // add tag for processor
+            assert(p == GCodeFormatter::quantize(p));
+            gcode += ";" + GCodeProcessor::reserved_tag(GCodeProcessor::ETags::Wipe_End) + "\n";
+            gcodegen.set_last_pos(gcodegen.gcode_to_point(p));
+        }
+    }
+
+    // Prevent wiping again on the same path.
+    this->reset_path();
+    return gcode;
+}
+
+// Make a little move inwards before leaving loop after path was extruded,
+// thus the current extruder position is at the end of a path and the path
+// may not be closed in case the loop was clipped to hide a seam.
+std::optional<Point> wipe_hide_seam(const SmoothPath &path, bool is_hole, double wipe_length)
+{
+    assert(! path.empty());
+    assert(path.front().path.size() >= 2);
+    assert(path.back().path.size() >= 2);
+
+    // Heuristics for estimating whether there is a chance that the wipe move will fit inside a small perimeter
+    // or that the wipe move direction could be calculated with reasonable accuracy.
+    if (longer_than(path, 2.5 * wipe_length)) {
+        // The print head will be moved away from path end inside the island.
+        Point p_current = path.back().path.back().point;
+        Point p_next = path.front().path.front().point;
+        Point p_prev;
+        {
+            // Is the seam hiding gap large enough already?
+            double l = wipe_length - (p_next - p_current).cast<double>().norm();
+            if (l > 0) {
+                // Not yet.
+                std::optional<Point> n = sample_path_point_at_distance_from_start(path, l);
+                assert(n);
+                if (! n)
+                    // Wipe move cannot be calculated, the loop is not long enough. This should not happen due to the longer_than() test above.
+                    return {};
+            }
+            if (std::optional<Point> p = sample_path_point_at_distance_from_end(path, wipe_length); p)
+                p_prev = *p;
+            else
+                // Wipe move cannot be calculated, the loop is not long enough. This should not happen due to the longer_than() test above.
+                return {};
+        }
+        // Detect angle between last and first segment.
+        // The side depends on the original winding order of the polygon (left for contours, right for holes).
+        double angle_inside = angle(p_next - p_current, p_prev - p_current);
+        assert(angle_inside >= -M_PI && angle_inside <= M_PI);
+        // 3rd of this angle will be taken, thus make the angle monotonic before interpolation.
+        if (is_hole) {
+            if (angle_inside > 0)
+                angle_inside -= 2.0 * M_PI;
+        } else {
+            if (angle_inside < 0)
+                angle_inside += 2.0 * M_PI;
+        }
+        // Rotate the forward segment inside by 1/3 of the wedge angle.
+        auto v_rotated = Eigen::Rotation2D(angle_inside) * (p_next - p_current).cast<double>().normalized();
+        return std::make_optional<Point>(p_current + (v_rotated * wipe_length).cast<coord_t>());
+    }
+
+    return {};
+}
+
+} // namespace Slic3r::GCode

src/libslic3r/GCode/Wipe.hpp

@@ -0,0 +1,73 @@
+#ifndef slic3r_GCode_Wipe_hpp_
+#define slic3r_GCode_Wipe_hpp_
+
+#include "SmoothPath.hpp"
+
+#include "../Geometry/ArcWelder.hpp"
+#include "../Point.hpp"
+#include "../PrintConfig.hpp"
+
+#include <cassert>
+#include <optional>
+
+namespace Slic3r {
+
+class GCodeGenerator;
+
+namespace GCode {
+
+class Wipe {
+public:
+    using Path = Slic3r::Geometry::ArcWelder::Path;
+
+    Wipe() = default;
+
+    void            init(const PrintConfig &config, const std::vector<unsigned int> &extruders);
+    void            enable(double wipe_len_max) { m_enabled = true; m_wipe_len_max = wipe_len_max; }
+    void            disable() { m_enabled = false; }
+    bool            enabled() const { return m_enabled; }
+
+    const Path&     path() const { return m_path; }
+    bool            has_path() const { assert(m_path.empty() || m_path.size() > 1); return ! m_path.empty(); }
+    void            reset_path() { m_path.clear(); m_offset = Point::Zero(); }
+    void            set_path(const Path &path) {
+        assert(path.empty() || path.size() > 1);
+        this->reset_path(); 
+        if (this->enabled() && path.size() > 1) 
+            m_path = path;
+    }
+    void            set_path(Path &&path) {
+        assert(path.empty() || path.size() > 1);
+        this->reset_path(); 
+        if (this->enabled() && path.size() > 1)
+            m_path = std::move(path);
+    }
+    void            set_path(SmoothPath &&path, bool reversed);
+    void            offset_path(const Point &v) { m_offset += v; }
+
+    std::string     wipe(GCodeGenerator &gcodegen, bool toolchange);
+
+    // Reduce feedrate a bit; travel speed is often too high to move on existing material.
+    // Too fast = ripping of existing material; too slow = short wipe path, thus more blob.
+    static double   calc_wipe_speed(const GCodeConfig &config) { return config.travel_speed.value * 0.8; }
+    // Reduce retraction length a bit to avoid effective retraction speed to be greater than the configured one
+    // due to rounding (TODO: test and/or better math for this).
+    static double   calc_xy_to_e_ratio(const GCodeConfig &config, unsigned int extruder_id) 
+        { return 0.95 * floor(config.retract_speed.get_at(extruder_id) + 0.5) / calc_wipe_speed(config); }
+
+private:
+    bool    m_enabled{ false };
+    // Maximum length of a path to accumulate. Only wipes shorter than this threshold will be requested.
+    double  m_wipe_len_max{ 0. };
+    Path    m_path;
+    // Offset from m_path to the current PrintObject active.
+    Point   m_offset{ Point::Zero() };
+};
+
+// Make a little move inwards before leaving loop.
+std::optional<Point> wipe_hide_seam(const SmoothPath &path, bool is_hole, double wipe_length);
+
+} // namespace GCode
+} // namespace Slic3r
+
+#endif // slic3r_GCode_Wipe_hpp_

src/libslic3r/GCode/WipeTower.hpp

@@ -1,5 +1,5 @@
-#ifndef WipeTower_
-#define WipeTower_
+#ifndef slic3r_GCode_WipeTower_hpp_
+#define slic3r_GCode_WipeTower_hpp_
 
 #include <cmath>
 #include <string>
@@ -411,4 +411,4 @@ private:
 
 } // namespace Slic3r
 
-#endif // WipeTowerPrusaMM_hpp_ 
+#endif // slic3r_GCode_WipeTower_hpp_ 

src/libslic3r/GCode/WipeTowerIntegration.cpp

@@ -0,0 +1,251 @@
+#include "WipeTowerIntegration.hpp"
+
+#include "../GCode.hpp"
+#include "../libslic3r.h"
+
+namespace Slic3r::GCode {
+
+static inline Point wipe_tower_point_to_object_point(GCodeGenerator &gcodegen, const Vec2f& wipe_tower_pt)
+{
+    return Point(scale_(wipe_tower_pt.x() - gcodegen.origin()(0)), scale_(wipe_tower_pt.y() - gcodegen.origin()(1)));
+}
+
+std::string WipeTowerIntegration::append_tcr(GCodeGenerator &gcodegen, const WipeTower::ToolChangeResult& tcr, int new_extruder_id, double z) const
+{
+    if (new_extruder_id != -1 && new_extruder_id != tcr.new_tool)
+        throw Slic3r::InvalidArgument("Error: WipeTowerIntegration::append_tcr was asked to do a toolchange it didn't expect.");
+
+    std::string gcode;
+
+    // Toolchangeresult.gcode assumes the wipe tower corner is at the origin (except for priming lines)
+    // We want to rotate and shift all extrusions (gcode postprocessing) and starting and ending position
+    float alpha = m_wipe_tower_rotation / 180.f * float(M_PI);
+
+    auto transform_wt_pt = [&alpha, this](const Vec2f& pt) -> Vec2f {
+        Vec2f out = Eigen::Rotation2Df(alpha) * pt;
+        out += m_wipe_tower_pos;
+        return out;
+    };
+
+    Vec2f start_pos = tcr.start_pos;
+    Vec2f end_pos = tcr.end_pos;
+    if (! tcr.priming) {
+        start_pos = transform_wt_pt(start_pos);
+        end_pos = transform_wt_pt(end_pos);
+    }
+
+    Vec2f wipe_tower_offset = tcr.priming ? Vec2f::Zero() : m_wipe_tower_pos;
+    float wipe_tower_rotation = tcr.priming ? 0.f : alpha;
+
+    std::string tcr_rotated_gcode = post_process_wipe_tower_moves(tcr, wipe_tower_offset, wipe_tower_rotation);
+
+    gcode += gcodegen.writer().unlift(); // Make sure there is no z-hop (in most cases, there isn't).
+
+    double current_z = gcodegen.writer().get_position().z();
+    if (z == -1.) // in case no specific z was provided, print at current_z pos
+        z = current_z;
+
+    const bool needs_toolchange = gcodegen.writer().need_toolchange(new_extruder_id);
+    const bool will_go_down = ! is_approx(z, current_z);
+    const bool is_ramming = (gcodegen.config().single_extruder_multi_material && ! tcr.priming)
+                             || (! gcodegen.config().single_extruder_multi_material && gcodegen.config().filament_multitool_ramming.get_at(tcr.initial_tool));
+    const bool should_travel_to_tower = tcr.force_travel        // wipe tower says so
+                                     || ! needs_toolchange      // this is just finishing the tower with no toolchange
+                                     || is_ramming;
+    if (should_travel_to_tower) {
+        gcode += gcodegen.retract();
+        gcodegen.m_avoid_crossing_perimeters.use_external_mp_once();
+        gcode += gcodegen.travel_to(
+            wipe_tower_point_to_object_point(gcodegen, start_pos),
+            ExtrusionRole::Mixed,
+            "Travel to a Wipe Tower");
+        gcode += gcodegen.unretract();
+    } else {
+        // When this is multiextruder printer without any ramming, we can just change
+        // the tool without travelling to the tower.
+    }
+
+    if (will_go_down) {
+        gcode += gcodegen.writer().retract();
+        gcode += gcodegen.writer().travel_to_z(z, "Travel down to the last wipe tower layer.");
+        gcode += gcodegen.writer().unretract();
+    }
+
+    std::string toolchange_gcode_str;
+    std::string deretraction_str;
+    if (tcr.priming || (new_extruder_id >= 0 && needs_toolchange)) {
+        if (is_ramming)
+            gcodegen.m_wipe.reset_path(); // We don't want wiping on the ramming lines.
+        toolchange_gcode_str = gcodegen.set_extruder(new_extruder_id, tcr.print_z); // TODO: toolchange_z vs print_z
+        if (gcodegen.config().wipe_tower)
+            deretraction_str = gcodegen.unretract();
+    }
+
+    
+
+
+    // Insert the toolchange and deretraction gcode into the generated gcode.
+    DynamicConfig config;
+    config.set_key_value("toolchange_gcode", new ConfigOptionString(toolchange_gcode_str));
+    config.set_key_value("deretraction_from_wipe_tower_generator", new ConfigOptionString(deretraction_str));
+    std::string tcr_gcode, tcr_escaped_gcode = gcodegen.placeholder_parser_process("tcr_rotated_gcode", tcr_rotated_gcode, new_extruder_id, &config);
+    unescape_string_cstyle(tcr_escaped_gcode, tcr_gcode);
+    gcode += tcr_gcode;
+    if (! toolchange_gcode_str.empty() && toolchange_gcode_str.back() != '\n')
+        toolchange_gcode_str += '\n';
+
+    // A phony move to the end position at the wipe tower.
+    gcodegen.writer().travel_to_xy(end_pos.cast<double>());
+    gcodegen.set_last_pos(wipe_tower_point_to_object_point(gcodegen, end_pos));
+    if (!is_approx(z, current_z)) {
+        gcode += gcodegen.writer().retract();
+        gcode += gcodegen.writer().travel_to_z(current_z, "Travel back up to the topmost object layer.");
+        gcode += gcodegen.writer().unretract();
+    }
+
+    else {
+        // Prepare a future wipe.
+        // Convert to a smooth path.
+        Geometry::ArcWelder::Path path;
+        path.reserve(tcr.wipe_path.size());
+        std::transform(tcr.wipe_path.begin(), tcr.wipe_path.end(), std::back_inserter(path),
+            [&gcodegen, &transform_wt_pt](const Vec2f &wipe_pt) { 
+                return Geometry::ArcWelder::Segment{ wipe_tower_point_to_object_point(gcodegen, transform_wt_pt(wipe_pt)) };
+            });
+        // Pass to the wipe cache.
+        gcodegen.m_wipe.set_path(std::move(path));
+    }
+
+    // Let the planner know we are traveling between objects.
+    gcodegen.m_avoid_crossing_perimeters.use_external_mp_once();
+    return gcode;
+}
+
+// This function postprocesses gcode_original, rotates and moves all G1 extrusions and returns resulting gcode
+// Starting position has to be supplied explicitely (otherwise it would fail in case first G1 command only contained one coordinate)
+std::string WipeTowerIntegration::post_process_wipe_tower_moves(const WipeTower::ToolChangeResult& tcr, const Vec2f& translation, float angle) const
+{
+    Vec2f extruder_offset = m_extruder_offsets[tcr.initial_tool].cast<float>();
+
+    std::istringstream gcode_str(tcr.gcode);
+    std::string gcode_out;
+    std::string line;
+    Vec2f pos = tcr.start_pos;
+    Vec2f transformed_pos = Eigen::Rotation2Df(angle) * pos + translation;
+    Vec2f old_pos(-1000.1f, -1000.1f);
+
+    while (gcode_str) {
+        std::getline(gcode_str, line);  // we read the gcode line by line
+
+        // All G1 commands should be translated and rotated. X and Y coords are
+        // only pushed to the output when they differ from last time.
+        // WT generator can override this by appending the never_skip_tag
+        if (boost::starts_with(line, "G1 ")) {
+            bool never_skip = false;
+            auto it = line.find(WipeTower::never_skip_tag());
+            if (it != std::string::npos) {
+                // remove the tag and remember we saw it
+                never_skip = true;
+                line.erase(it, it + WipeTower::never_skip_tag().size());
+            }
+            std::ostringstream line_out;
+            std::istringstream line_str(line);
+            line_str >> std::noskipws;  // don't skip whitespace
+            char ch = 0;
+            line_str >> ch >> ch; // read the "G1"
+            while (line_str >> ch) {
+                if (ch == 'X' || ch == 'Y')
+                    line_str >> (ch == 'X' ? pos.x() : pos.y());
+                else
+                    line_out << ch;
+            }
+
+            transformed_pos = Eigen::Rotation2Df(angle) * pos + translation;
+
+            if (transformed_pos != old_pos || never_skip) {
+                line = line_out.str();
+                boost::trim_left(line); // Remove leading spaces
+                std::ostringstream oss;
+                oss << std::fixed << std::setprecision(3) << "G1";
+                if (transformed_pos.x() != old_pos.x() || never_skip)
+                    oss << " X" << transformed_pos.x() - extruder_offset.x();
+                if (transformed_pos.y() != old_pos.y() || never_skip)
+                    oss << " Y" << transformed_pos.y() - extruder_offset.y();
+                if (! line.empty())
+                    oss << " ";
+                line = oss.str() + line;
+                old_pos = transformed_pos;
+            }
+        }
+
+        gcode_out += line + "\n";
+
+        // If this was a toolchange command, we should change current extruder offset
+        if (line == "[toolchange_gcode]") {
+            extruder_offset = m_extruder_offsets[tcr.new_tool].cast<float>();
+
+            // If the extruder offset changed, add an extra move so everything is continuous
+            if (extruder_offset != m_extruder_offsets[tcr.initial_tool].cast<float>()) {
+                std::ostringstream oss;
+                oss << std::fixed << std::setprecision(3)
+                    << "G1 X" << transformed_pos.x() - extruder_offset.x()
+                    << " Y" << transformed_pos.y() - extruder_offset.y()
+                    << "\n";
+                gcode_out += oss.str();
+            }
+        }
+    }
+    return gcode_out;
+}
+
+
+std::string WipeTowerIntegration::prime(GCodeGenerator &gcodegen)
+{
+    std::string gcode;
+    for (const WipeTower::ToolChangeResult& tcr : m_priming) {
+        if (! tcr.extrusions.empty())
+            gcode += append_tcr(gcodegen, tcr, tcr.new_tool);
+    }
+    return gcode;
+}
+
+std::string WipeTowerIntegration::tool_change(GCodeGenerator &gcodegen, int extruder_id, bool finish_layer)
+{
+    std::string gcode;
+    assert(m_layer_idx >= 0);
+    if (gcodegen.writer().need_toolchange(extruder_id) || finish_layer) {
+        if (m_layer_idx < (int)m_tool_changes.size()) {
+            if (!(size_t(m_tool_change_idx) < m_tool_changes[m_layer_idx].size()))
+                throw Slic3r::RuntimeError("Wipe tower generation failed, possibly due to empty first layer.");
+
+            // Calculate where the wipe tower layer will be printed. -1 means that print z will not change,
+            // resulting in a wipe tower with sparse layers.
+            double wipe_tower_z = -1;
+            bool ignore_sparse = false;
+            if (gcodegen.config().wipe_tower_no_sparse_layers.value) {
+                wipe_tower_z = m_last_wipe_tower_print_z;
+                ignore_sparse = (m_tool_changes[m_layer_idx].size() == 1 && m_tool_changes[m_layer_idx].front().initial_tool == m_tool_changes[m_layer_idx].front().new_tool && m_layer_idx != 0);
+                if (m_tool_change_idx == 0 && !ignore_sparse)
+                    wipe_tower_z = m_last_wipe_tower_print_z + m_tool_changes[m_layer_idx].front().layer_height;
+            }
+
+            if (!ignore_sparse) {
+                gcode += append_tcr(gcodegen, m_tool_changes[m_layer_idx][m_tool_change_idx++], extruder_id, wipe_tower_z);
+                m_last_wipe_tower_print_z = wipe_tower_z;
+            }
+        }
+    }
+    return gcode;
+}
+
+// Print is finished. Now it remains to unload the filament safely with ramming over the wipe tower.
+std::string WipeTowerIntegration::finalize(GCodeGenerator &gcodegen)
+{
+    std::string gcode;
+    if (std::abs(gcodegen.writer().get_position().z() - m_final_purge.print_z) > EPSILON)
+        gcode += gcodegen.change_layer(m_final_purge.print_z);
+    gcode += append_tcr(gcodegen, m_final_purge, -1);
+    return gcode;
+}
+
+} // namespace Slic3r::GCode

src/libslic3r/GCode/WipeTowerIntegration.hpp

@@ -0,0 +1,65 @@
+#ifndef slic3r_GCode_WipeTowerIntegration_hpp_
+#define slic3r_GCode_WipeTowerIntegration_hpp_
+
+#include "WipeTower.hpp"
+#include "../PrintConfig.hpp"
+
+namespace Slic3r {
+
+class GCodeGenerator;
+
+namespace GCode {
+
+class WipeTowerIntegration {
+public:
+    WipeTowerIntegration(
+        const PrintConfig                                           &print_config,
+        const std::vector<WipeTower::ToolChangeResult>              &priming,
+        const std::vector<std::vector<WipeTower::ToolChangeResult>> &tool_changes,
+        const WipeTower::ToolChangeResult                           &final_purge) :
+        m_left(/*float(print_config.wipe_tower_x.value)*/ 0.f),
+        m_right(float(/*print_config.wipe_tower_x.value +*/ print_config.wipe_tower_width.value)),
+        m_wipe_tower_pos(float(print_config.wipe_tower_x.value), float(print_config.wipe_tower_y.value)),
+        m_wipe_tower_rotation(float(print_config.wipe_tower_rotation_angle)),
+        m_extruder_offsets(print_config.extruder_offset.values),
+        m_priming(priming),
+        m_tool_changes(tool_changes),
+        m_final_purge(final_purge),
+        m_layer_idx(-1),
+        m_tool_change_idx(0)
+    {}
+
+    std::string prime(GCodeGenerator &gcodegen);
+    void next_layer() { ++ m_layer_idx; m_tool_change_idx = 0; }
+    std::string tool_change(GCodeGenerator &gcodegen, int extruder_id, bool finish_layer);
+    std::string finalize(GCodeGenerator &gcodegen);
+    std::vector<float> used_filament_length() const;
+
+private:
+    WipeTowerIntegration& operator=(const WipeTowerIntegration&);
+    std::string append_tcr(GCodeGenerator &gcodegen, const WipeTower::ToolChangeResult &tcr, int new_extruder_id, double z = -1.) const;
+
+    // Postprocesses gcode: rotates and moves G1 extrusions and returns result
+    std::string post_process_wipe_tower_moves(const WipeTower::ToolChangeResult& tcr, const Vec2f& translation, float angle) const;
+
+    // Left / right edges of the wipe tower, for the planning of wipe moves.
+    const float                                                  m_left;
+    const float                                                  m_right;
+    const Vec2f                                                  m_wipe_tower_pos;
+    const float                                                  m_wipe_tower_rotation;
+    const std::vector<Vec2d>                                     m_extruder_offsets;
+
+    // Reference to cached values at the Printer class.
+    const std::vector<WipeTower::ToolChangeResult>              &m_priming;
+    const std::vector<std::vector<WipeTower::ToolChangeResult>> &m_tool_changes;
+    const WipeTower::ToolChangeResult                           &m_final_purge;
+    // Current layer index.
+    int                                                          m_layer_idx;
+    int                                                          m_tool_change_idx;
+    double                                                       m_last_wipe_tower_print_z = 0.f;
+};
+
+} // namespace GCode
+} // namespace Slic3r
+
+#endif // slic3r_GCode_WipeTowerIntegration_hpp_ 

src/libslic3r/Geometry/ArcWelder.cpp

@@ -0,0 +1,674 @@
+// The following code for merging circles into arches originates from https://github.com/FormerLurker/ArcWelderLib
+
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// Arc Welder: Anti-Stutter Library
+//
+// Compresses many G0/G1 commands into G2/G3(arc) commands where possible, ensuring the tool paths stay within the specified resolution.
+// This reduces file size and the number of gcodes per second.
+//
+// Uses the 'Gcode Processor Library' for gcode parsing, position processing, logging, and other various functionality.
+//
+// Copyright(C) 2021 - Brad Hochgesang
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// This program is free software : you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.See the
+// GNU Affero General Public License for more details.
+//
+//
+// You can contact the author at the following email address: 
+// FormerLurker@pm.me
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+#include "ArcWelder.hpp"
+#include "Circle.hpp"
+
+#include "../MultiPoint.hpp"
+#include "../Polygon.hpp"
+
+#include <numeric>
+#include <random>
+#include <boost/log/trivial.hpp>
+
+namespace Slic3r { namespace Geometry { namespace ArcWelder {
+
+Points arc_discretize(const Point &p1, const Point &p2, const double radius, const bool ccw, const double deviation)
+{
+    Vec2d  center = arc_center(p1.cast<double>(), p2.cast<double>(), radius, ccw);
+    double angle  = arc_angle(p1.cast<double>(), p2.cast<double>(), radius);
+    assert(angle > 0);
+
+    double r           = std::abs(radius);
+    size_t num_steps   = arc_discretization_steps(r, angle, deviation);
+    double angle_step  = angle / num_steps;
+
+    Points out;
+    out.reserve(num_steps + 1);
+    out.emplace_back(p1);
+    if (! ccw)
+        angle_step *= -1.;
+    for (size_t i = 1; i < num_steps; ++ i)
+        out.emplace_back(p1.rotated(angle_step * i, center.cast<coord_t>()));
+    out.emplace_back(p2);
+    return out;
+}
+
+struct Circle
+{
+    Point  center;
+    double radius;
+};
+
+// Interpolate three points with a circle.
+// Returns false if the three points are collinear or if the radius is bigger than maximum allowed radius.
+static std::optional<Circle> try_create_circle(const Point &p1, const Point &p2, const Point &p3, const double max_radius)
+{
+    if (auto center = Slic3r::Geometry::try_circle_center(p1.cast<double>(), p2.cast<double>(), p3.cast<double>(), SCALED_EPSILON); center) {
+        Point c = center->cast<coord_t>();
+        if (double r = sqrt(double((c - p1).cast<int64_t>().squaredNorm())); r <= max_radius)
+            return std::make_optional<Circle>({ c, float(r) });
+    }
+    return {};
+}
+
+// Returns a closest point on the segment.
+// Returns false if the closest point is not inside the segment, but at its boundary.
+static bool foot_pt_on_segment(const Point &p1, const Point &p2, const Point &pt, Point &out)
+{
+    Vec2i64 v21 = (p2 - p1).cast<int64_t>();
+    int64_t l2  = v21.squaredNorm();
+    if (l2 > int64_t(SCALED_EPSILON)) {
+        if (int64_t t = (pt - p1).cast<int64_t>().dot(v21);
+            t >= int64_t(SCALED_EPSILON) && t < l2 - int64_t(SCALED_EPSILON)) {
+            out = p1 + ((double(t) / double(l2)) * v21.cast<double>()).cast<coord_t>();
+            return true;
+        }
+    }
+    // The segment is short or the closest point is an end point.
+    return false;
+}
+
+static inline bool circle_approximation_sufficient(const Circle &circle, const Points::const_iterator begin, const Points::const_iterator end, const double tolerance)
+{
+    // The circle was calculated from the 1st and last point of the point sequence, thus the fitting of those points does not need to be evaluated.
+    assert(std::abs((*begin - circle.center).cast<double>().norm() - circle.radius) < SCALED_EPSILON);
+    assert(std::abs((*std::prev(end) - circle.center).cast<double>().norm() - circle.radius) < SCALED_EPSILON);
+    assert(end - begin >= 3);
+
+    // Test the 1st point.
+    if (double distance_from_center = (*begin - circle.center).cast<double>().norm();
+        std::abs(distance_from_center - circle.radius) > tolerance)
+        return false;
+
+    for (auto it = std::next(begin); it != end; ++ it) {
+        if (double distance_from_center = (*it - circle.center).cast<double>().norm();
+            std::abs(distance_from_center - circle.radius) > tolerance)
+            return false;
+        Point closest_point;
+        if (foot_pt_on_segment(*std::prev(it), *it, circle.center, closest_point)) {
+            if (double distance_from_center = (closest_point - circle.center).cast<double>().norm();
+                std::abs(distance_from_center - circle.radius) > tolerance)
+                return false;
+        }
+    }
+    return true;
+}
+
+static inline bool get_deviation_sum_squared(const Circle &circle, const Points::const_iterator begin, const Points::const_iterator end, const double tolerance, double &total_deviation)
+{
+    // The circle was calculated from the 1st and last point of the point sequence, thus the fitting of those points does not need to be evaluated.
+    assert(std::abs((*begin - circle.center).cast<double>().norm() - circle.radius) < SCALED_EPSILON);
+    assert(std::abs((*std::prev(end) - circle.center).cast<double>().norm() - circle.radius) < SCALED_EPSILON);
+    assert(end - begin >= 3);
+
+    total_deviation = 0;
+
+    const double tolerance2 = sqr(tolerance);
+    for (auto it = std::next(begin); std::next(it) != end; ++ it)
+        if (double deviation2 = sqr((*it - circle.center).cast<double>().norm() - circle.radius); deviation2 > tolerance2)
+            return false;
+        else
+            total_deviation += deviation2;
+
+    for (auto it = begin; std::next(it) != end; ++ it) {
+        Point closest_point;
+        if (foot_pt_on_segment(*it, *std::next(it), circle.center, closest_point)) {
+            if (double deviation2 = sqr((closest_point - circle.center).cast<double>().norm() - circle.radius); deviation2 > tolerance2)
+                return false;
+            else
+                total_deviation += deviation2;
+        }
+    }
+
+    return true;
+}
+
+static std::optional<Circle> try_create_circle(const Points::const_iterator begin, const Points::const_iterator end, const double max_radius, const double tolerance)
+{
+    std::optional<Circle> out;
+    size_t size = end - begin;
+    if (size == 3) {
+        out = try_create_circle(*begin, *std::next(begin), *std::prev(end), max_radius);
+        if (out && ! circle_approximation_sufficient(*out, begin, end, tolerance))
+            out.reset();
+    } else {
+#if 0
+        size_t ipivot = size / 2;
+        // Take a center difference of points at the center of the path.
+        //FIXME does it really help? For short arches, the linear interpolation may be 
+        Point pivot = (size % 2 == 0) ? (*(begin + ipivot) + *(begin + ipivot - 1)) / 2 :
+            (*(begin + ipivot - 1) + *(begin + ipivot + 1)) / 2;
+        if (std::optional<Circle> circle = try_create_circle(*begin, pivot, *std::prev(end), max_radius);
+            circle && circle_approximation_sufficient(*circle, begin, end, tolerance))
+            return circle;
+#endif
+        // Find the circle with the least deviation, if one exists.
+        double least_deviation = std::numeric_limits<double>::max();
+        double current_deviation;
+        for (auto it = std::next(begin); std::next(it) != end; ++ it)
+            if (std::optional<Circle> circle = try_create_circle(*begin, *it, *std::prev(end), max_radius); 
+                circle && get_deviation_sum_squared(*circle, begin, end, tolerance, current_deviation)) {
+                if (current_deviation < least_deviation) {
+                    out = circle;
+                    least_deviation = current_deviation;
+                }
+            }
+    }
+    return out;
+}
+
+// ported from ArcWelderLib/ArcWelder/segmented/shape.h class "arc"
+class Arc {
+public:
+    Point  start_point;
+    Point  end_point;
+    Point  center;
+    double radius;
+    Orientation direction { Orientation::Unknown };
+};
+
+static inline int sign(const int64_t i)
+{
+    return i > 0 ? 1 : i < 0 ? -1 : 0;
+}
+
+// Return orientation of a polyline with regard to the center.
+// Successive points are expected to take less than a PI angle step.
+Orientation arc_orientation(
+    const Point                 &center,
+    const Points::const_iterator begin,
+    const Points::const_iterator end)
+{
+    assert(end - begin >= 3);
+    // Assumption: Two successive points of a single segment span an angle smaller than PI.
+    Vec2i64 vstart  = (*begin - center).cast<int64_t>();
+    Vec2i64 vprev   = vstart;
+    int     arc_dir = 0;
+    for (auto it = std::next(begin); it != end; ++ it) {
+        Vec2i64 v = (*it - center).cast<int64_t>();
+        int     dir = sign(cross2(vprev, v));
+        if (dir == 0) {
+            // Ignore radial segments.
+        } else if (arc_dir * dir < 0) {
+            // The path turns back and overextrudes. Such path is likely invalid, but the arc interpolation should
+            // rather maintain such an invalid path instead of covering it up.
+            // Don't replace such a path with an arc.
+            return {};
+        } else {
+            // Success, either establishing the direction for the first time, or moving in the same direction as the last time.
+            arc_dir = dir;
+            vprev = v;
+        }
+    }
+    return arc_dir == 0 ? 
+        // All points are radial wrt. the center, this is unexpected.
+        Orientation::Unknown :
+        // Arc is valid, either CCW or CW.
+        arc_dir > 0 ? Orientation::CCW : Orientation::CW;
+}
+
+static inline std::optional<Arc> try_create_arc_impl(
+    const Circle                &circle,
+    const Points::const_iterator begin,
+    const Points::const_iterator end,
+    const double                 tolerance,
+    const double                 path_tolerance_percent)
+{
+    assert(end - begin >= 3);
+    // Assumption: Two successive points of a single segment span an angle smaller than PI.
+    Orientation orientation = arc_orientation(circle.center, begin, end);
+    if (orientation == Orientation::Unknown)
+        return {};
+
+    Vec2i64 vstart = (*begin - circle.center).cast<int64_t>();
+    Vec2i64 vend   = (*std::prev(end) - circle.center).cast<int64_t>();
+    double  angle  = atan2(double(cross2(vstart, vend)), double(vstart.dot(vend)));
+    if (orientation == Orientation::CW)
+        angle *= -1.;
+    if (angle < 0)
+        angle += 2. * M_PI;
+    assert(angle >= 0. && angle < 2. * M_PI + EPSILON);
+
+    // Check the length against the original length.
+    // This can trigger simply due to the differing path lengths
+    // but also could indicate that the vector calculation above
+    // got wrong direction
+    const double arc_length                     = circle.radius * angle;
+    const double approximate_length             = length(begin, end);
+    assert(approximate_length > 0);
+    const double arc_length_difference_relative = (arc_length - approximate_length) / approximate_length;
+
+    if (std::fabs(arc_length_difference_relative) >= path_tolerance_percent) {
+        return {};
+    } else {
+        assert(circle_approximation_sufficient(circle, begin, end, tolerance + SCALED_EPSILON));
+        return std::make_optional<Arc>(Arc{
+            *begin,
+            *std::prev(end),
+            circle.center,
+            angle > M_PI ? - circle.radius : circle.radius,
+            orientation
+        });
+    }
+}
+
+static inline std::optional<Arc> try_create_arc(
+    const Points::const_iterator begin,
+    const Points::const_iterator end,
+    double                       max_radius             = default_scaled_max_radius,
+    double                       tolerance              = default_scaled_resolution,
+    double                       path_tolerance_percent = default_arc_length_percent_tolerance)
+{
+    std::optional<Circle> circle = try_create_circle(begin, end, max_radius, tolerance);
+    if (! circle)
+        return {};
+    return try_create_arc_impl(*circle, begin, end, tolerance, path_tolerance_percent);
+}
+
+float arc_angle(const Vec2f &start_pos, const Vec2f &end_pos, Vec2f &center_pos, bool is_ccw)
+{
+    if ((end_pos - start_pos).squaredNorm() < sqr(1e-6)) {
+        // If start equals end, full circle is considered.
+        return float(2. * M_PI);
+    } else {
+        Vec2f v1 = start_pos - center_pos;
+        Vec2f v2 = end_pos   - center_pos;
+        if (! is_ccw)
+            std::swap(v1, v2);
+        float radian = atan2(cross2(v1, v2), v1.dot(v2));
+        return radian < 0 ? float(2. * M_PI) + radian : radian;
+    }
+}
+
+float arc_length(const Vec2f &start_pos, const Vec2f &end_pos, Vec2f &center_pos, bool is_ccw)
+{
+    return (center_pos - start_pos).norm() * arc_angle(start_pos, end_pos, center_pos, is_ccw);
+}
+
+// Reduces polyline in the <begin, end) range in place,
+// returns the new end iterator.
+static inline Segments::iterator douglas_peucker_in_place(Segments::iterator begin, Segments::iterator end, const double tolerance)
+{
+    return douglas_peucker<int64_t>(begin, end, begin, tolerance, [](const Segment &s) { return s.point; });
+}
+
+Path fit_path(const Points &src, double tolerance, double fit_circle_percent_tolerance)
+{
+    assert(tolerance >= 0);
+    assert(fit_circle_percent_tolerance >= 0);
+
+    Path out;
+    out.reserve(src.size());
+    if (tolerance <= 0 || src.size() <= 2) {
+        // No simplification, just convert.
+        std::transform(src.begin(), src.end(), std::back_inserter(out), [](const Point &p) -> Segment { return { p }; });
+    } else if (fit_circle_percent_tolerance <= 0) {
+        // Convert and simplify to a polyline.
+        std::transform(src.begin(), src.end(), std::back_inserter(out), [](const Point &p) -> Segment { return { p }; });
+        out.erase(douglas_peucker_in_place(out.begin(), out.end(), tolerance), out.end());
+    } else {
+        // Perform simplification & fitting.
+        // Index of the start of a last polyline, which has not yet been decimated.
+        int begin_pl_idx = 0;
+        out.push_back({ src.front(), 0.f });
+        for (auto it = std::next(src.begin()); it != src.end();) {
+            // Minimum 2 additional points required for circle fitting.
+            auto begin = std::prev(it);
+            auto end   = std::next(it);
+            assert(end <= src.end());
+            std::optional<Arc> arc;
+            while (end != src.end()) {
+                auto next_end = std::next(end);
+                if (std::optional<Arc> this_arc = try_create_arc(
+                                                        begin, next_end,
+                                                        ArcWelder::default_scaled_max_radius,
+                                                        tolerance, fit_circle_percent_tolerance);
+                    this_arc) {
+                    assert(this_arc->direction != Orientation::Unknown);
+                    arc = this_arc;
+                    end = next_end;
+                } else
+                    break;
+            }
+            if (arc) {
+                // If there is a trailing polyline, decimate it first before saving a new arc.
+                if (out.size() - begin_pl_idx > 2) {
+                    // Decimating linear segmens only.
+                    assert(std::all_of(out.begin() + begin_pl_idx + 1, out.end(), [](const Segment &seg) { return seg.linear(); }));
+                    out.erase(douglas_peucker_in_place(out.begin() + begin_pl_idx, out.end(), tolerance), out.end());
+                    assert(out.back().linear());
+                }
+                // Save the index of an end of the new circle segment, which may become the first point of a possible future polyline.
+                begin_pl_idx = int(out.size());
+                // This will be the next point to try to add.
+                it = end;
+                // Add the new arc.
+                assert(*begin == arc->start_point);
+                assert(*std::prev(it) == arc->end_point);
+                assert(out.back().point == arc->start_point);
+                out.push_back({ arc->end_point, float(arc->radius), arc->direction });
+#if 0
+                // Verify that all the source points are at tolerance distance from the interpolated path.
+                {
+                    const Segment &seg_start = *std::prev(std::prev(out.end()));
+                    const Segment &seg_end   = out.back();
+                    const Vec2d    center    = arc_center(seg_start.point.cast<double>(), seg_end.point.cast<double>(), double(seg_end.radius), seg_end.ccw());
+                    assert(seg_start.point == *begin);
+                    assert(seg_end.point == *std::prev(end));
+                    assert(arc_orientation(center.cast<coord_t>(), begin, end) == arc->direction);
+                    for (auto it = std::next(begin); it != end; ++ it) {
+                        Point  ptstart = *std::prev(it);
+                        Point  ptend   = *it;
+                        Point  closest_point;
+                        if (foot_pt_on_segment(ptstart, ptend, center.cast<coord_t>(), closest_point)) {
+                            double distance_from_center = (closest_point.cast<double>() - center).norm();
+                            assert(std::abs(distance_from_center - std::abs(seg_end.radius)) < tolerance + SCALED_EPSILON);
+                        }
+                        Vec2d  v     = (ptend - ptstart).cast<double>();
+                        double len   = v.norm();
+                        auto num_segments = std::min<size_t>(10, ceil(2. * len / fit_circle_percent_tolerance));
+                        for (size_t i = 0; i < num_segments; ++ i) {
+                            Point p = ptstart + (v * (double(i) / double(num_segments))).cast<coord_t>();
+                            assert(i == 0 || inside_arc_wedge(seg_start.point.cast<double>(), seg_end.point.cast<double>(), center, seg_end.radius > 0, seg_end.ccw(), p.cast<double>()));
+                            double d2 = sqr((p.cast<double>() - center).norm() - std::abs(seg_end.radius));
+                            assert(d2 < sqr(tolerance + SCALED_EPSILON));
+                        }
+                    }
+                }
+#endif
+            } else {
+                // Arc is not valid, append a linear segment.
+                out.push_back({ *it ++ });
+            }
+        }
+        if (out.size() - begin_pl_idx > 2)
+            // Do the final polyline decimation.
+            out.erase(douglas_peucker_in_place(out.begin() + begin_pl_idx, out.end(), tolerance), out.end());
+    }
+
+#if 0
+    // Verify that all the source points are at tolerance distance from the interpolated path.
+    for (auto it = std::next(src.begin()); it != src.end(); ++ it) {
+        Point  start = *std::prev(it);
+        Point  end   = *it;
+        Vec2d  v     = (end - start).cast<double>();
+        double len   = v.norm();
+        auto num_segments = std::min<size_t>(10, ceil(2. * len / fit_circle_percent_tolerance));
+        for (size_t i = 0; i <= num_segments; ++ i) {
+            Point p = start + (v * (double(i) / double(num_segments))).cast<coord_t>();
+            PathSegmentProjection proj = point_to_path_projection(out, p);
+            assert(proj.valid());
+            assert(proj.distance2 < sqr(tolerance + SCALED_EPSILON));
+        }
+    }
+#endif
+
+    return out;
+}
+
+void reverse(Path &path)
+{
+    if (path.size() > 1) {
+        auto prev = path.begin();
+        for (auto it = std::next(prev); it != path.end(); ++ it) {
+            prev->radius      = it->radius;
+            prev->orientation = it->orientation == Orientation::CCW ? Orientation::CW : Orientation::CCW;
+            prev = it;
+        }
+        path.back().radius = 0;
+        std::reverse(path.begin(), path.end());
+    }
+}
+
+double clip_start(Path &path, const double len)
+{
+    reverse(path);
+    double remaining = clip_end(path, len);
+    reverse(path);
+    // Return remaining distance to go.
+    return remaining;
+}
+
+double clip_end(Path &path, double distance)
+{
+    while (distance > 0) {
+        Segment &last = path.back();
+        path.pop_back();
+        if (path.empty())
+            break;
+        if (last.linear()) {
+            // Linear segment
+            Vec2d  v    = (path.back().point - last.point).cast<double>();
+            double lsqr = v.squaredNorm();
+            if (lsqr > sqr(distance)) {
+                path.push_back({ last.point + (v * (distance / sqrt(lsqr))).cast<coord_t>() });
+                // Length to go is zero.
+                return 0;
+            }
+            distance -= sqrt(lsqr);
+        } else {
+            // Circular segment
+            double angle = arc_angle(path.back().point.cast<double>(), last.point.cast<double>(), last.radius);
+            double len   = std::abs(last.radius) * angle;
+            if (len > distance) {
+                // Rotate the segment end point in reverse towards the start point.
+                if (last.ccw())
+                    angle *= -1.;
+                path.push_back({
+                    last.point.rotated(angle * (distance / len),
+                        arc_center(path.back().point.cast<double>(), last.point.cast<double>(), double(last.radius), last.ccw()).cast<coord_t>()),
+                    last.radius, last.orientation });
+                // Length to go is zero.
+                return 0;
+            }
+            distance -= len;
+        }
+    }
+
+    // Return remaining distance to go.
+    assert(distance >= 0);
+    return distance;
+}
+
+PathSegmentProjection point_to_path_projection(const Path &path, const Point &point, double search_radius2)
+{
+    assert(path.size() != 1);
+    // initialized to "invalid" state.
+    PathSegmentProjection out;
+    out.distance2 = search_radius2;
+    if (path.size() < 2 || path.front().point == point) {
+        // First point is the closest point.
+        if (path.empty()) {
+            // No closest point available.
+        } else if (const Point p0 = path.front().point; p0 == point) {
+            out.segment_id = 0;
+            out.point      = p0;
+            out.distance2  = 0;
+        } else if (double d2 = (p0 - point).cast<double>().squaredNorm(); d2 < out.distance2) {
+            out.segment_id = 0;
+            out.point      = p0;
+            out.distance2  = d2;
+        }
+    } else {
+        assert(path.size() >= 2);
+        // min_point_it will contain an end point of a segment with a closest projection found
+        // or path.cbegin() if no such closest projection closer than search_radius2 was found.
+        auto  min_point_it = path.cbegin();
+        Point prev         = path.front().point;
+        for (auto it = std::next(path.cbegin()); it != path.cend(); ++ it) {
+            if (it->linear()) {
+                // Linear segment
+                Point proj;
+                // distance_to_squared() will possibly return the start or end point of a line segment.
+                if (double d2 = line_alg::distance_to_squared(Line(prev, it->point), point, &proj); d2 < out.distance2) {
+                    out.point     = proj;
+                    out.distance2 = d2;
+                    min_point_it  = it;
+                }
+            } else {
+                // Circular arc
+                Vec2i64 center = arc_center(prev.cast<double>(), it->point.cast<double>(), double(it->radius), it->ccw()).cast<int64_t>();
+                // Test whether point is inside the wedge.
+                Vec2i64 v1 = prev.cast<int64_t>() - center;
+                Vec2i64 v2 = it->point.cast<int64_t>() - center;
+                Vec2i64 vp = point.cast<int64_t>() - center;
+                if (inside_arc_wedge_vectors(v1, v2, it->radius > 0, it->ccw(), vp)) {
+                    // Distance of the radii.
+                    const auto r = double(std::abs(it->radius));
+                    const auto rtest = sqrt(double(vp.squaredNorm()));
+                    if (double d2 = sqr(rtest - r); d2 < out.distance2) {
+                        if (rtest > SCALED_EPSILON)
+                            // Project vp to the arc.
+                            out.point = center.cast<coord_t>() + (vp.cast<double>() * (r / rtest)).cast<coord_t>();
+                        else
+                            // Test point is very close to the center of the radius. Any point of the arc is the closest.
+                            // Pick the start.
+                            out.point = prev;
+                        out.distance2 = d2;
+                        out.center = center.cast<coord_t>();
+                        min_point_it  = it;
+                    }
+                } else {
+                    // Distance to the start point.
+                    if (double d2 = double((v1 - vp).squaredNorm()); d2 < out.distance2) {
+                        out.point     = prev;
+                        out.distance2 = d2;
+                        min_point_it  = it;
+                    }
+                }
+            }
+            prev = it->point;
+        }
+        if (! path.back().linear()) {
+            // Calculate distance to the end point.
+            if (double d2 = (path.back().point - point).cast<double>().squaredNorm(); d2 < out.distance2) {
+                out.point     = path.back().point;
+                out.distance2 = d2;
+                min_point_it  = std::prev(path.end());
+            }
+        }
+        // If a new closes point was found, it is closer than search_radius2.
+        assert((min_point_it == path.cbegin()) == (out.distance2 == search_radius2));
+        // Output is not valid yet.
+        assert(! out.valid());
+        if (min_point_it != path.cbegin()) {
+            // Make it valid by setting the segment.
+            out.segment_id = std::prev(min_point_it) - path.begin();
+            assert(out.valid());
+        }
+    }
+
+    assert(! out.valid() || (out.segment_id >= 0 && out.segment_id < path.size()));
+    return out;
+}
+
+std::pair<Path, Path> split_at(const Path &path, const PathSegmentProjection &proj, const double min_segment_length)
+{
+    assert(proj.valid());
+    assert(! proj.valid() || (proj.segment_id >= 0 && proj.segment_id < path.size()));
+    assert(path.size() > 1);
+    std::pair<Path, Path> out;
+    if (! proj.valid() || proj.segment_id + 1 == path.size() || (proj.segment_id + 2 == path.size() && proj.point == path.back().point))
+        out.first = path;
+    else if (proj.segment_id == 0 && proj.point == path.front().point)
+        out.second = path;
+    else {
+        // Path will likely be split to two pieces.
+        assert(proj.valid() && proj.segment_id >= 0 && proj.segment_id + 1 < path.size());
+        const Segment &start = path[proj.segment_id];
+        const Segment &end   = path[proj.segment_id + 1];
+        bool           split_segment = true;
+        int            split_segment_id = proj.segment_id;
+        if (int64_t d2 = (proj.point - start.point).cast<int64_t>().squaredNorm(); d2 < sqr(min_segment_length)) {
+            split_segment = false;
+            int64_t d22 = (proj.point - end.point).cast<int64_t>().squaredNorm();
+            if (d22 < d2)
+                // Split at the end of the segment.
+                ++ split_segment_id;
+        } else if (int64_t d2 = (proj.point - end.point).cast<int64_t>().squaredNorm(); d2 < sqr(min_segment_length)) {
+            ++ split_segment_id;
+            split_segment = false;
+        }
+        if (split_segment) {
+            out.first.assign(path.begin(), path.begin() + split_segment_id + 2);
+            out.second.assign(path.begin() + split_segment_id, path.end());
+            assert(out.first[out.first.size() - 2] == start);
+            assert(out.first.back() == end);
+            assert(out.second.front() == start);
+            assert(out.second[1] == end);
+            assert(out.first.size() + out.second.size() == path.size() + 2);
+            assert(out.first.back().radius == out.second[1].radius);
+            out.first.back().point = proj.point;
+            out.second.front().point = proj.point;
+            if (end.radius < 0) {
+                // A large arc (> PI) was split.
+                // At least one of the two arches that were created by splitting the original arch will become smaller.
+                // Make the radii of those arches that became < PI positive.
+                // In case of a projection onto an arc, proj.center should be filled in and valid.
+                auto vstart = (start.point - proj.center).cast<int64_t>();
+                auto vend   = (end.point - proj.center).cast<int64_t>();
+                auto vproj  = (proj.point - proj.center).cast<int64_t>();
+                if ((cross2(vstart, vproj) > 0) == end.ccw())
+                    // Make the radius of a minor arc positive.
+                    out.first.back().radius *= -1.f;
+                if ((cross2(vproj, vend) > 0) == end.ccw())
+                    // Make the radius of a minor arc positive.
+                    out.second[1].radius *= -1.f;
+                assert(out.first.size() > 1);
+                assert(out.second.size() > 1);
+                out.second.front().radius = 0;
+            }
+        } else {
+            assert(split_segment_id >= 0 && split_segment_id < path.size());
+            if (split_segment_id + 1 == int(path.size()))
+                out.first = path;
+            else if (split_segment_id == 0)
+                out.second = path;
+            else {
+                // Split at the start of proj.segment_id.
+                out.first.assign(path.begin(), path.begin() + split_segment_id + 1);
+                out.second.assign(path.begin() + split_segment_id, path.end());
+                assert(out.first.size() + out.second.size() == path.size() + 1);
+                assert(out.first.back() == (split_segment_id == proj.segment_id ? start : end));
+                assert(out.second.front() == (split_segment_id == proj.segment_id ? start : end));
+                assert(out.first.size() > 1);
+                assert(out.second.size() > 1);
+                out.second.front().radius = 0;
+            }
+        }
+    }
+
+    return out;
+}
+
+std::pair<Path, Path> split_at(const Path &path, const Point &point, const double min_segment_length)
+{
+    return split_at(path, point_to_path_projection(path, point), min_segment_length);
+}
+
+} } } // namespace Slic3r::Geometry::ArcWelder

src/libslic3r/Geometry/ArcWelder.hpp

@@ -0,0 +1,324 @@
+#ifndef slic3r_Geometry_ArcWelder_hpp_
+#define slic3r_Geometry_ArcWelder_hpp_
+
+#include <optional>
+
+#include "../Point.hpp"
+
+namespace Slic3r { namespace Geometry { namespace ArcWelder {
+
+// Calculate center point of an arc given two points and a radius.
+// positive radius: take shorter arc
+// negative radius: take longer arc
+// radius must NOT be zero!
+template<typename Derived, typename Derived2, typename Float>
+inline Eigen::Matrix<Float, 2, 1, Eigen::DontAlign> arc_center(
+    const Eigen::MatrixBase<Derived>   &start_pos,
+    const Eigen::MatrixBase<Derived2>  &end_pos, 
+    const Float                         radius,
+    const bool                          is_ccw)
+{
+    static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "arc_center(): first parameter is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "arc_center(): second parameter is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value, "arc_center(): Both vectors must be of the same type.");
+    static_assert(std::is_same<typename Derived::Scalar, Float>::value, "arc_center(): Radius must be of the same type as the vectors.");
+    assert(radius != 0);
+    using Vector = Eigen::Matrix<Float, 2, 1, Eigen::DontAlign>;
+    auto  v  = end_pos - start_pos;
+    Float q2 = v.squaredNorm();
+    assert(q2 > 0);
+    Float t2 = sqr(radius) / q2 - Float(.25f);
+    // If the start_pos and end_pos are nearly antipodal, t2 may become slightly negative.
+    // In that case return a centroid of start_point & end_point.
+    Float t = t2 > 0 ? sqrt(t2) : Float(0);
+    auto mid = Float(0.5) * (start_pos + end_pos);
+    Vector vp{ -v.y() * t, v.x() * t };
+    return (radius > Float(0)) == is_ccw ? (mid + vp).eval() : (mid - vp).eval();
+}
+
+// Calculate angle of an arc given two points and a radius.
+// Returned angle is in the range <0, 2 PI)
+// positive radius: take shorter arc
+// negative radius: take longer arc
+// radius must NOT be zero!
+template<typename Derived, typename Derived2>
+inline typename Derived::Scalar arc_angle(
+    const Eigen::MatrixBase<Derived>   &start_pos,
+    const Eigen::MatrixBase<Derived2>  &end_pos, 
+    const typename Derived::Scalar      radius)
+{
+    static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "arc_angle(): first parameter is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "arc_angle(): second parameter is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value, "arc_angle(): Both vectors must be of the same type.");
+    assert(radius != 0);
+    using Float = typename Derived::Scalar;
+    Float a = Float(0.5) * (end_pos - start_pos).norm() / radius;
+    return radius > Float(0) ?
+        // acute angle:
+        (a > Float( 1.) ? Float(M_PI) : Float(2.) * std::asin(a)) :
+        // obtuse angle:
+        (a < Float(-1.) ? Float(M_PI) : Float(2. * M_PI) + Float(2.) * std::asin(a));
+}
+
+// Calculate positive length of an arc given two points and a radius.
+// positive radius: take shorter arc
+// negative radius: take longer arc
+// radius must NOT be zero!
+template<typename Derived, typename Derived2>
+inline typename Derived::Scalar arc_length(
+    const Eigen::MatrixBase<Derived>   &start_pos,
+    const Eigen::MatrixBase<Derived2>  &end_pos,
+    const typename Derived::Scalar      radius)
+{
+    static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "arc_length(): first parameter is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "arc_length(): second parameter is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value, "arc_length(): Both vectors must be of the same type.");
+    assert(radius != 0);
+    return arc_angle(start_pos, end_pos, radius) * std::abs(radius);
+}
+
+// Calculate positive length of an arc given two points, center and orientation.
+template<typename Derived, typename Derived2, typename Derived3>
+inline typename Derived::Scalar arc_length(
+    const Eigen::MatrixBase<Derived>   &start_pos,
+    const Eigen::MatrixBase<Derived2>  &end_pos,
+    const Eigen::MatrixBase<Derived3>  &center_pos,
+    const bool                          ccw)
+{
+    static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "arc_length(): first parameter is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "arc_length(): second parameter is not a 2D vector");
+    static_assert(Derived3::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "arc_length(): third parameter is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value &&
+                  std::is_same<typename Derived::Scalar, typename Derived3::Scalar>::value, "arc_length(): All third points must be of the same type.");
+    using Float = typename Derived::Scalar;
+    auto  vstart = start_pos - center_pos;
+    auto  vend   = end_pos - center_pos;
+    Float radius = vstart.norm();
+    Float angle  = atan2(double(cross2(vstart, vend)), double(vstart.dot(vend)));
+    if (! ccw)
+        angle *= Float(-1.);
+    if (angle < 0)
+        angle += Float(2. * M_PI);
+    assert(angle >= Float(0.) && angle < Float(2. * M_PI + EPSILON));
+    return angle * radius;
+}
+
+// Test whether a point is inside a wedge of an arc.
+template<typename Derived, typename Derived2, typename Derived3>
+inline bool inside_arc_wedge_vectors(
+    const Eigen::MatrixBase<Derived>    &start_vec,
+    const Eigen::MatrixBase<Derived2>   &end_vec,
+    const bool                           shorter_arc,
+    const bool                           ccw,
+    const Eigen::MatrixBase<Derived3>   &query_vec)
+{
+    static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "inside_arc_wedge_vectors(): start_vec is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "inside_arc_wedge_vectors(): end_vec is not a 2D vector");
+    static_assert(Derived3::IsVectorAtCompileTime && int(Derived3::SizeAtCompileTime) == 2, "inside_arc_wedge_vectors(): query_vec is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value &&
+                  std::is_same<typename Derived::Scalar, typename Derived3::Scalar>::value, "inside_arc_wedge_vectors(): All vectors must be of the same type.");
+    return shorter_arc ?
+        // Smaller (convex) wedge.
+        (ccw ?
+            cross2(start_vec, query_vec) > 0 && cross2(query_vec, end_vec) > 0 :
+            cross2(start_vec, query_vec) < 0 && cross2(query_vec, end_vec) < 0) :
+        // Larger (concave) wedge.
+        (ccw ?
+            cross2(end_vec, query_vec) < 0 || cross2(query_vec, start_vec) < 0 :
+            cross2(end_vec, query_vec) > 0 || cross2(query_vec, start_vec) > 0);
+}
+
+template<typename Derived, typename Derived2, typename Derived3, typename Derived4>
+inline bool inside_arc_wedge(
+    const Eigen::MatrixBase<Derived>    &start_pt,
+    const Eigen::MatrixBase<Derived2>   &end_pt,
+    const Eigen::MatrixBase<Derived3>   &center_pt,
+    const bool                           shorter_arc,
+    const bool                           ccw,
+    const Eigen::MatrixBase<Derived4>   &query_pt)
+{
+    static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "inside_arc_wedge(): start_pt is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "inside_arc_wedge(): end_pt is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived3::SizeAtCompileTime) == 2, "inside_arc_wedge(): center_pt is not a 2D vector");
+    static_assert(Derived3::IsVectorAtCompileTime && int(Derived4::SizeAtCompileTime) == 2, "inside_arc_wedge(): query_pt is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value &&
+        std::is_same<typename Derived::Scalar, typename Derived3::Scalar>::value &&
+        std::is_same<typename Derived::Scalar, typename Derived4::Scalar>::value, "inside_arc_wedge(): All vectors must be of the same type.");
+    return inside_arc_wedge_vectors(start_pt - center_pt, end_pt - center_pt, shorter_arc, ccw, query_pt - center_pt);
+}
+
+template<typename Derived, typename Derived2, typename Derived3, typename Float>
+inline bool inside_arc_wedge(
+    const Eigen::MatrixBase<Derived>    &start_pt,
+    const Eigen::MatrixBase<Derived2>   &end_pt,
+    const Float                          radius,
+    const bool                           ccw,
+    const Eigen::MatrixBase<Derived3>   &query_pt)
+{
+    static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "inside_arc_wedge(): start_pt is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "inside_arc_wedge(): end_pt is not a 2D vector");
+    static_assert(Derived3::IsVectorAtCompileTime && int(Derived3::SizeAtCompileTime) == 2, "inside_arc_wedge(): query_pt is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value &&
+        std::is_same<typename Derived::Scalar, typename Derived3::Scalar>::value &&
+        std::is_same<typename Derived::Scalar, Float>::value, "inside_arc_wedge(): All vectors + radius must be of the same type.");
+    return inside_arc_wedge(start_pt, end_pt,
+        arc_center(start_pt, end_pt, radius, ccw), 
+        radius > 0, ccw, query_pt);
+}
+
+// Return number of linear segments necessary to interpolate arc of a given positive radius and positive angle to satisfy
+// maximum deviation of an interpolating polyline from an analytic arc.
+template<typename FloatType>
+size_t arc_discretization_steps(const FloatType radius, const FloatType angle, const FloatType deviation)
+{
+    assert(radius > 0);
+    assert(angle > 0);
+    assert(angle <= FloatType(2. * M_PI));
+    assert(deviation > 0);
+
+    FloatType d = radius - deviation;
+    return d < EPSILON ?
+        // Radius smaller than deviation.
+        (   // Acute angle: a single segment interpolates the arc with sufficient accuracy.
+            angle < M_PI || 
+            // Obtuse angle: Test whether the furthest point (center) of an arc is closer than deviation to the center of a line segment.
+            radius * (FloatType(1.) + cos(M_PI - FloatType(.5) * angle)) < deviation ?
+            // Single segment is sufficient
+            1 :
+            // Two segments are necessary, the middle point is at the center of the arc.
+            2) :
+        size_t(ceil(angle / (2. * acos(d / radius))));
+}
+
+// Discretize arc given the radius, orientation and maximum deviation from the arc.
+// Returned polygon starts with p1, ends with p2 and it is discretized to guarantee the maximum deviation.
+Points arc_discretize(const Point &p1, const Point &p2, const double radius, const bool ccw, const double deviation);
+
+// 1.2m diameter, maximum given by coord_t
+static constexpr const double default_scaled_max_radius = scaled<double>(600.);
+// 0.05mm
+static constexpr const double default_scaled_resolution = scaled<double>(0.05);
+// 5 percent
+static constexpr const double default_arc_length_percent_tolerance = 0.05;
+
+enum class Orientation : unsigned char {
+    Unknown,
+    CCW,
+    CW,
+};
+
+// Returns orientation of a polyline with regard to the center.
+// Successive points are expected to take less than a PI angle step.
+// Returns Orientation::Unknown if the orientation with regard to the center 
+// is not monotonous.
+Orientation arc_orientation(
+    const Point                 &center,
+    const Points::const_iterator begin,
+    const Points::const_iterator end);
+
+// Single segment of a smooth path.
+struct Segment
+{
+    // End point of a linear or circular segment.
+    // Start point is provided by the preceding segment.
+    Point       point;
+    // Radius of a circular segment. Positive - take the shorter arc. Negative - take the longer arc. Zero - linear segment.
+    float       radius{ 0.f };
+    // CCW or CW. Ignored for zero radius (linear segment).
+    Orientation orientation{ Orientation::CCW };
+
+    bool    linear() const { return radius == 0; }
+    bool    ccw() const { return orientation == Orientation::CCW; }
+    bool    cw() const { return orientation == Orientation::CW; }
+};
+
+inline bool operator==(const Segment &lhs, const Segment &rhs) {
+    return lhs.point == rhs.point && lhs.radius == rhs.radius && lhs.orientation == rhs.orientation;
+}
+
+using Segments = std::vector<Segment>;
+using Path = Segments;
+
+// Interpolate polyline path with a sequence of linear / circular segments given the interpolation tolerance.
+// Only convert to polyline if zero tolerance.
+// Convert to polyline and decimate polyline if zero fit_circle_percent_tolerance.
+// Path fitting is inspired with the arc fitting algorithm in
+//      Arc Welder: Anti-Stutter Library by Brad Hochgesang FormerLurker@pm.me
+//      https://github.com/FormerLurker/ArcWelderLib 
+Path fit_path(const Points &points, double tolerance, double fit_circle_percent_tolerance);
+
+// Decimate polyline into a smooth path structure using Douglas-Peucker polyline decimation algorithm.
+inline Path fit_polyline(const Points &points, double tolerance) { return fit_path(points, tolerance, 0.); }
+
+template<typename FloatType>
+inline FloatType segment_length(const Segment &start, const Segment &end)
+{
+    return end.linear() ?
+        (end.point - start.point).cast<FloatType>().norm() :
+        arc_length(start.point.cast<FloatType>(), end.point.cast<FloatType>(), FloatType(end.radius));
+}
+
+template<typename FloatType>
+inline FloatType path_length(const Path &path)
+{
+    FloatType len = 0;
+    for (size_t i = 1; i < path.size(); ++ i)
+        len += segment_length<FloatType>(path[i - 1], path[i]);
+    return len;
+}
+
+// Estimate minimum path length of a segment cheaply without having to calculate center of an arc and it arc length.
+// Used for caching a smooth path chunk that is certainly longer than a threshold.
+inline int64_t estimate_min_segment_length(const Segment &start, const Segment &end)
+{
+    if (end.linear() || end.radius > 0) {
+        // Linear segment or convex wedge, take the larger X or Y component.
+        Point v = (end.point - start.point).cwiseAbs();
+        return std::max(v.x(), v.y());
+    } else {
+        // Arc with angle > PI.
+        // Returns estimate of PI * r
+        return - int64_t(3) * int64_t(end.radius);
+    }
+}
+
+// Estimate minimum path length cheaply without having to calculate center of an arc and it arc length.
+// Used for caching a smooth path chunk that is certainly longer than a threshold.
+inline int64_t estimate_path_length(const Path &path)
+{
+    int64_t len = 0;
+    for (size_t i = 1; i < path.size(); ++ i)
+        len += Geometry::ArcWelder::estimate_min_segment_length(path[i - 1], path[i]);
+    return len;
+}
+
+void reverse(Path &path);
+
+// Clip start / end of a smooth path by len.
+// If path is shorter than len, remaining path length to trim will be returned.
+double clip_start(Path &path, const double len);
+double clip_end(Path &path, const double len);
+
+struct PathSegmentProjection
+{
+    // Start segment of a projection on the path.
+    size_t segment_id { std::numeric_limits<size_t>::max() };
+    // Projection of the point on the segment.
+    Point  point      { 0, 0 };
+    // If the point lies on an arc, the arc center is cached here.
+    Point  center     { 0, 0 };
+    // Square of a distance of the projection.
+    double distance2  { std::numeric_limits<double>::max() };
+
+    bool   valid() const { return this->segment_id != std::numeric_limits<size_t>::max(); }
+};
+// Returns closest segment and a parameter along the closest segment of a path to a point.
+PathSegmentProjection point_to_path_projection(const Path &path, const Point &point, double search_radius2 = std::numeric_limits<double>::max());
+// Split a path into two paths at a segment point. Snap to an existing point if the projection of "point is closer than min_segment_length.
+std::pair<Path, Path> split_at(const Path &path, const PathSegmentProjection &proj, const double min_segment_length);
+// Split a path into two paths at a point closest to "point". Snap to an existing point if the projection of "point is closer than min_segment_length.
+std::pair<Path, Path> split_at(const Path &path, const Point &point, const double min_segment_length);
+
+} } } // namespace Slic3r::Geometry::ArcWelder
+
+#endif // slic3r_Geometry_ArcWelder_hpp_

src/libslic3r/Geometry/Circle.cpp

@@ -17,9 +17,14 @@ Point circle_center_taubin_newton(const Points::const_iterator& input_begin, con
 	return Point::new_scale(center.x(), center.y());
 }
 
-/// Adapted from work in "Circular and Linear Regression: Fitting circles and lines by least squares", pg 126
-/// Returns a point corresponding to the center of a circle for which all of the points from input_begin to input_end
-/// lie on.
+// Robust and accurate algebraic circle fit, which works well even if data points are observed only within a small arc.
+// The method was proposed by G. Taubin in
+//      "Estimation Of Planar Curves, Surfaces And Nonplanar Space Curves Defined By Implicit Equations, 
+//       With Applications To Edge And Range Image Segmentation", IEEE Trans. PAMI, Vol. 13, pages 1115-1138, (1991)."
+// This particular implementation was adapted from
+//      "Circular and Linear Regression: Fitting circles and lines by least squares", pg 126"
+// Returns a point corresponding to the center of a circle for which all of the points from input_begin to input_end
+// lie on.
 Vec2d circle_center_taubin_newton(const Vec2ds::const_iterator& input_begin, const Vec2ds::const_iterator& input_end, size_t cycles)
 {
     // calculate the centroid of the data set

src/libslic3r/Geometry/Circle.hpp

@@ -9,10 +9,17 @@ namespace Slic3r { namespace Geometry {
 
 // https://en.wikipedia.org/wiki/Circumscribed_circle
 // Circumcenter coordinates, Cartesian coordinates
-template<typename Vector>
-Vector circle_center(const Vector &a, const Vector &bsrc, const Vector &csrc, typename Vector::Scalar epsilon)
+// In case the three points are collinear, returns their centroid.
+template<typename Derived, typename Derived2, typename Derived3>
+Eigen::Matrix<typename Derived::Scalar, 2, 1, Eigen::DontAlign> circle_center(const Derived &a, const Derived2 &bsrc, const Derived3 &csrc, typename Derived::Scalar epsilon)
 {
-    using Scalar = typename Vector::Scalar;
+    static_assert(Derived ::IsVectorAtCompileTime && int(Derived ::SizeAtCompileTime) == 2, "circle_center(): 1st point is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "circle_center(): 2nd point is not a 2D vector");
+    static_assert(Derived3::IsVectorAtCompileTime && int(Derived3::SizeAtCompileTime) == 2, "circle_center(): 3rd point is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value && std::is_same<typename Derived::Scalar, typename Derived3::Scalar>::value, 
+        "circle_center(): All three points must be of the same type.");
+    using Scalar = typename Derived::Scalar;
+    using Vector = Eigen::Matrix<Scalar, 2, 1, Eigen::DontAlign>;
     Vector b  = bsrc - a;
     Vector c  = csrc - a;
 	Scalar lb = b.squaredNorm();
@@ -30,6 +37,32 @@ Vector circle_center(const Vector &a, const Vector &bsrc, const Vector &csrc, ty
     }
 }
 
+// https://en.wikipedia.org/wiki/Circumscribed_circle
+// Circumcenter coordinates, Cartesian coordinates
+// Returns no value if the three points are collinear.
+template<typename Derived, typename Derived2, typename Derived3>
+std::optional<Eigen::Matrix<typename Derived::Scalar, 2, 1, Eigen::DontAlign>> try_circle_center(const Derived &a, const Derived2 &bsrc, const Derived3 &csrc, typename Derived::Scalar epsilon)
+{
+    static_assert(Derived ::IsVectorAtCompileTime && int(Derived ::SizeAtCompileTime) == 2, "try_circle_center(): 1st point is not a 2D vector");
+    static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "try_circle_center(): 2nd point is not a 2D vector");
+    static_assert(Derived3::IsVectorAtCompileTime && int(Derived3::SizeAtCompileTime) == 2, "try_circle_center(): 3rd point is not a 2D vector");
+    static_assert(std::is_same<typename Derived::Scalar, typename Derived2::Scalar>::value && std::is_same<typename Derived::Scalar, typename Derived3::Scalar>::value, 
+        "try_circle_center(): All three points must be of the same type.");
+    using Scalar = typename Derived::Scalar;
+    using Vector = Eigen::Matrix<Scalar, 2, 1, Eigen::DontAlign>;
+    Vector b  = bsrc - a;
+    Vector c  = csrc - a;
+    Scalar lb = b.squaredNorm();
+    Scalar lc = c.squaredNorm();
+    if (Scalar d = b.x() * c.y() - b.y() * c.x(); std::abs(d) < epsilon) {
+        // The three points are collinear.
+        return {};
+    } else {
+        Vector v = lc * b - lb * c;
+        return std::make_optional<Vector>(a + Vector(- v.y(), v.x()) / (2 * d));
+    }
+}
+
 // 2D circle defined by its center and squared radius
 template<typename Vector>
 struct CircleSq {
@@ -65,7 +98,7 @@ struct Circle {
     Vector center;
     Scalar radius;
 
-    Circle() {}
+    Circle() = default;
     Circle(const Vector &center, const Scalar radius) : center(center), radius(radius) {}
     Circle(const Vector &a, const Vector &b) : center(Scalar(0.5) * (a + b)) { radius = (a - center).norm(); }
     Circle(const Vector &a, const Vector &b, const Vector &c, const Scalar epsilon) { *this = CircleSq(a, b, c, epsilon); }

src/libslic3r/Model.cpp

@@ -27,7 +27,7 @@
 
 #include "SVG.hpp"
 #include <Eigen/Dense>
-#include "GCodeWriter.hpp"
+#include "GCode/GCodeWriter.hpp"
 
 namespace Slic3r {
 

src/libslic3r/MultiPoint.cpp

@@ -103,100 +103,6 @@ bool MultiPoint::remove_duplicate_points()
     return false;
 }
 
-Points MultiPoint::douglas_peucker(const Points &pts, const double tolerance)
-{
-    Points result_pts;
-	auto tolerance_sq = int64_t(sqr(tolerance));
-    if (! pts.empty()) {
-        const Point  *anchor      = &pts.front();
-        size_t        anchor_idx  = 0;
-        const Point  *floater     = &pts.back();
-        size_t        floater_idx = pts.size() - 1;
-        result_pts.reserve(pts.size());
-        result_pts.emplace_back(*anchor);
-        if (anchor_idx != floater_idx) {
-            assert(pts.size() > 1);
-            std::vector<size_t> dpStack;
-            dpStack.reserve(pts.size());
-            dpStack.emplace_back(floater_idx);
-            for (;;) {
-                int64_t max_dist_sq  = 0;
-                size_t  furthest_idx = anchor_idx;
-                // find point furthest from line seg created by (anchor, floater) and note it
-                {
-                    const Point   a = *anchor;
-                    const Point   f = *floater;
-                    const Vec2i64 v = (f - a).cast<int64_t>();
-                    if (const int64_t l2 = v.squaredNorm(); l2 == 0) {
-                        for (size_t i = anchor_idx + 1; i < floater_idx; ++ i)
-                            if (int64_t dist_sq = (pts[i] - a).cast<int64_t>().squaredNorm(); dist_sq > max_dist_sq) {
-                                max_dist_sq  = dist_sq;
-                                furthest_idx = i;
-                            }
-                    } else {
-                        const double dl2 = double(l2);
-                        const Vec2d  dv  = v.cast<double>();
-                        for (size_t i = anchor_idx + 1; i < floater_idx; ++ i) {
-                            const Point   p  = pts[i];
-                            const Vec2i64 va = (p  - a).template cast<int64_t>();
-                            const int64_t t  = va.dot(v);
-                            int64_t dist_sq;
-                            if (t <= 0) {
-                                dist_sq = va.squaredNorm();
-                            } else if (t >= l2) {
-                                dist_sq = (p - f).cast<int64_t>().squaredNorm();
-                            } else {
-                                const Vec2i64 w = ((double(t) / dl2) * dv).cast<int64_t>();
-                                dist_sq = (w - va).squaredNorm();
-                            }
-                            if (dist_sq > max_dist_sq) {
-                                max_dist_sq  = dist_sq;
-                                furthest_idx = i;
-                            }
-                        }                        
-                    }
-                }
-                // remove point if less than tolerance
-                if (max_dist_sq <= tolerance_sq) {
-                    result_pts.emplace_back(*floater);
-                    anchor_idx = floater_idx;
-                    anchor     = floater;
-                    assert(dpStack.back() == floater_idx);
-                    dpStack.pop_back();
-                    if (dpStack.empty())
-                        break;
-                    floater_idx = dpStack.back();
-                } else {
-                    floater_idx = furthest_idx;
-                    dpStack.emplace_back(floater_idx);
-                }
-                floater = &pts[floater_idx];
-            }
-        }
-        assert(result_pts.front() == pts.front());
-        assert(result_pts.back()  == pts.back());
-
-#if 0
-        {
-            static int iRun = 0;
-			BoundingBox bbox(pts);
-			BoundingBox bbox2(result_pts);
-			bbox.merge(bbox2);
-            SVG svg(debug_out_path("douglas_peucker_%d.svg", iRun ++).c_str(), bbox);
-            if (pts.front() == pts.back())
-                svg.draw(Polygon(pts), "black");
-            else
-                svg.draw(Polyline(pts), "black");
-            if (result_pts.front() == result_pts.back())
-                svg.draw(Polygon(result_pts), "green", scale_(0.1));
-            else
-                svg.draw(Polyline(result_pts), "green", scale_(0.1));
-        }
-#endif
-    }
-    return result_pts;
-}
-
 // Visivalingam simplification algorithm https://github.com/slic3r/Slic3r/pull/3825
 // thanks to @fuchstraumer
 /*
@@ -219,7 +125,7 @@ struct vis_node{
     // other node if it's area is less than the other node's area
     bool operator<(const vis_node& other) { return (this->area < other.area); }
 };
-Points MultiPoint::visivalingam(const Points& pts, const double& tolerance)
+Points MultiPoint::visivalingam(const Points &pts, const double tolerance)
 {
     // Make sure there's enough points in "pts" to bother with simplification.
     assert(pts.size() >= 2);

src/libslic3r/MultiPoint.hpp

@@ -12,6 +12,123 @@ namespace Slic3r {
 class BoundingBox;
 class BoundingBox3;
 
+// Reduces polyline in the <begin, end) range, outputs into the output iterator.
+// Output iterator may be equal to input iterator as long as the iterator value type move operator supports move at the same input / output address.
+template<typename SquareLengthType, typename InputIterator, typename OutputIterator, typename PointGetter>
+inline OutputIterator douglas_peucker(InputIterator begin, InputIterator end, OutputIterator out, const double tolerance, PointGetter point_getter)
+{
+    using InputIteratorCategory = typename std::iterator_traits<InputIterator>::iterator_category;
+    static_assert(std::is_base_of_v<std::input_iterator_tag, InputIteratorCategory>);
+    using Vector = Eigen::Matrix<SquareLengthType, 2, 1, Eigen::DontAlign>;
+    if (begin != end) {
+        // Supporting in-place reduction and the data type may be generic, thus we are always making a copy of the point value before there is a chance
+        // to override input by moving the data to the output.
+        auto a = point_getter(*begin);
+        *out ++ = std::move(*begin);
+        if (auto next = std::next(begin); next == end) {
+            // Single point input only.
+        } else if (std::next(next) == end) {
+            // Two points input.
+            *out ++ = std::move(*next);
+        } else {
+            const auto tolerance_sq = SquareLengthType(sqr(tolerance));
+            InputIterator anchor  = begin;
+            InputIterator floater = std::prev(end);
+            std::vector<InputIterator> dpStack;
+            if constexpr (std::is_base_of_v<std::random_access_iterator_tag, InputIteratorCategory>)
+                dpStack.reserve(end - begin);
+            dpStack.emplace_back(floater);
+            auto f = point_getter(*floater);
+            for (;;) {
+                assert(anchor != floater);
+                bool            take_floater = false;
+                InputIterator   furthest     = anchor;
+                if (std::next(anchor) == floater) {
+                    // Two point segment. Accept the floater.
+                    take_floater = true;
+                } else {
+                    SquareLengthType max_dist_sq = 0;
+                    // Find point furthest from line seg created by (anchor, floater) and note it.
+                    const Vector v = (f - a).template cast<SquareLengthType>();
+                    if (const SquareLengthType l2 = v.squaredNorm(); l2 == 0) {
+                        // Zero length segment, find the furthest point between anchor and floater.
+                        for (auto it = std::next(anchor); it != floater; ++ it)
+                            if (SquareLengthType dist_sq = (point_getter(*it) - a).template cast<SquareLengthType>().squaredNorm(); 
+                                dist_sq > max_dist_sq) {
+                                max_dist_sq  = dist_sq;
+                                furthest = it;
+                            }
+                    } else {
+                        // Find Find the furthest point from the line <anchor, floater>.
+                        const double dl2 = double(l2);
+                        const Vec2d  dv  = v.template cast<double>();
+                        for (auto it = std::next(anchor); it != floater; ++ it) {
+                            const auto   p  = point_getter(*it);
+                            const Vector va = (p - a).template cast<SquareLengthType>();
+                            const SquareLengthType t = va.dot(v);
+                            SquareLengthType dist_sq;
+                            if (t <= 0) {
+                                dist_sq = va.squaredNorm();
+                            } else if (t >= l2) {
+                                dist_sq = (p - f).template cast<SquareLengthType>().squaredNorm();
+                            } else if (double dt = double(t) / dl2; dt <= 0) {
+                                dist_sq = va.squaredNorm();
+                            } else if (dt >= 1.) {
+                                dist_sq = (p - f).template cast<SquareLengthType>().squaredNorm();
+                            } else {
+                                const Vector w = (dt * dv).cast<SquareLengthType>();
+                                dist_sq = (w - va).squaredNorm();
+                            }
+                            if (dist_sq > max_dist_sq) {
+                                max_dist_sq  = dist_sq;
+                                furthest     = it;
+                            }
+                        }                        
+                    }
+                    // remove point if less than tolerance
+                    take_floater = max_dist_sq <= tolerance_sq;
+                }
+                if (take_floater) {
+                    // The points between anchor and floater are close to the <anchor, floater> line.
+                    // Drop the points between them.
+                    a = f;
+                    *out ++ = std::move(*floater);
+                    anchor = floater;
+                    assert(dpStack.back() == floater);
+                    dpStack.pop_back();
+                    if (dpStack.empty())
+                        break;
+                    floater = dpStack.back();
+                    f = point_getter(*floater);
+                } else {
+                    // The furthest point is too far from the segment <anchor, floater>. 
+                    // Divide recursively.
+                    floater = furthest;
+                    f = point_getter(*floater);
+                    dpStack.emplace_back(floater);
+                }
+            }
+        }
+    }
+    return out;
+}
+
+// Reduces polyline in the <begin, end) range, outputs into the output iterator.
+// Output iterator may be equal to input iterator as long as the iterator value type move operator supports move at the same input / output address.
+template<typename OutputIterator>
+inline OutputIterator douglas_peucker(Points::const_iterator begin, Points::const_iterator end, OutputIterator out, const double tolerance)
+{
+    return douglas_peucker<int64_t>(begin, end, out, tolerance, [](const Point &p) { return p; });
+}
+
+inline Points douglas_peucker(const Points &src, const double tolerance) 
+{
+    Points out;
+    out.reserve(src.size());
+    douglas_peucker(src.begin(), src.end(), std::back_inserter(out), tolerance);
+    return out;
+}
+
 class MultiPoint
 {
 public:
@@ -81,8 +198,8 @@ public:
         }
     }
 
-    static Points douglas_peucker(const Points &points, const double tolerance);
-    static Points visivalingam(const Points& pts, const double& tolerance);
+    static Points douglas_peucker(const Points &src, const double tolerance) { return Slic3r::douglas_peucker(src, tolerance); }
+    static Points visivalingam(const Points &src, const double tolerance);
 
     inline auto begin()        { return points.begin(); }
     inline auto begin()  const { return points.begin(); }
@@ -119,16 +236,20 @@ extern BoundingBox get_extents(const MultiPoint &mp);
 extern BoundingBox get_extents_rotated(const Points &points, double angle);
 extern BoundingBox get_extents_rotated(const MultiPoint &mp, double angle);
 
-inline double length(const Points &pts) {
+inline double length(const Points::const_iterator begin, const Points::const_iterator end) {
     double total = 0;
-    if (! pts.empty()) {
-        auto it = pts.begin();
-        for (auto it_prev = it ++; it != pts.end(); ++ it, ++ it_prev)
+    if (begin != end) {
+        auto it = begin;
+        for (auto it_prev = it ++; it != end; ++ it, ++ it_prev)
             total += (*it - *it_prev).cast<double>().norm();
     }
     return total;
 }
 
+inline double length(const Points &pts) {
+    return length(pts.begin(), pts.end());
+}
+
 inline double area(const Points &polygon) {
     double area = 0.;
     for (size_t i = 0, j = polygon.size() - 1; i < polygon.size(); j = i ++)

src/libslic3r/PerimeterGenerator.cpp

@@ -119,20 +119,18 @@ ExtrusionMultiPath PerimeterGenerator::thick_polyline_to_multi_path(const ThickP
 
         const double w        = fmax(line.a_width, line.b_width);
         const Flow   new_flow = (role.is_bridge() && flow.bridge()) ? flow : flow.with_width(unscale<float>(w) + flow.height() * float(1. - 0.25 * PI));
-        if (path.polyline.points.empty()) {
-            path.polyline.append(line.a);
-            path.polyline.append(line.b);
+        if (path.empty()) {
             // Convert from spacing to extrusion width based on the extrusion model
             // of a square extrusion ended with semi circles.
+            path = { ExtrusionAttributes{ path.role(), new_flow } };
+            path.polyline.append(line.a);
+            path.polyline.append(line.b);
             #ifdef SLIC3R_DEBUG
             printf("  filling %f gap\n", flow.width);
             #endif
-            path.mm3_per_mm  = new_flow.mm3_per_mm();
-            path.width       = new_flow.width();
-            path.height      = new_flow.height();
         } else {
-            assert(path.width >= EPSILON);
-            thickness_delta = scaled<double>(fabs(path.width - new_flow.width()));
+            assert(path.width() >= EPSILON);
+            thickness_delta = scaled<double>(fabs(path.width() - new_flow.width()));
             if (thickness_delta <= merge_tolerance) {
                 // the width difference between this line and the current flow
                 // (of the previous line) width is within the accepted tolerance
@@ -325,10 +323,12 @@ static ExtrusionEntityCollection traverse_loops_classic(const PerimeterGenerator
             extrusion_paths_append(
                 paths,
                 intersection_pl({ polygon }, lower_slices_polygons_clipped),
+                ExtrusionAttributes{
                     role_normal,
-                is_external ? params.ext_mm3_per_mm           : params.mm3_per_mm,
+                    ExtrusionFlow{ is_external ? params.ext_mm3_per_mm : params.mm3_per_mm,
                                    is_external ? params.ext_perimeter_flow.width() : params.perimeter_flow.width(),
-                float(params.layer_height));
+                                   float(params.layer_height)
+                } });
             
             // get overhang paths by checking what parts of this loop fall 
             // outside the grown lower slices (thus where the distance between
@@ -336,21 +336,24 @@ static ExtrusionEntityCollection traverse_loops_classic(const PerimeterGenerator
             extrusion_paths_append(
                 paths,
                 diff_pl({ polygon }, lower_slices_polygons_clipped),
+                ExtrusionAttributes{
                     role_overhang,
-                params.mm3_per_mm_overhang,
-                params.overhang_flow.width(),
-                params.overhang_flow.height());
+                    ExtrusionFlow{ params.mm3_per_mm_overhang, params.overhang_flow.width(), params.overhang_flow.height() }
+                });
             
             // Reapply the nearest point search for starting point.
             // We allow polyline reversal because Clipper may have randomly reversed polylines during clipping.
             chain_and_reorder_extrusion_paths(paths, &paths.front().first_point());
         } else {
-            ExtrusionPath path(role_normal);
-            path.polyline   = polygon.split_at_first_point();
-            path.mm3_per_mm = is_external ? params.ext_mm3_per_mm             : params.mm3_per_mm;
-            path.width      = is_external ? params.ext_perimeter_flow.width() : params.perimeter_flow.width();
-            path.height     = float(params.layer_height);
-            paths.push_back(path);
+            paths.emplace_back(polygon.split_at_first_point(),
+                ExtrusionAttributes{
+                    role_normal,
+                    ExtrusionFlow{
+                        is_external ? params.ext_mm3_per_mm : params.mm3_per_mm,
+                        is_external ? params.ext_perimeter_flow.width() : params.perimeter_flow.width(),
+                        float(params.layer_height)
+                    }
+                });
         }
        
         coll.append(ExtrusionLoop(std::move(paths), loop_role));
@@ -383,11 +386,13 @@ static ExtrusionEntityCollection traverse_loops_classic(const PerimeterGenerator
             ExtrusionLoop *eloop = static_cast<ExtrusionLoop*>(coll.entities[idx.first]);
             coll.entities[idx.first] = nullptr;
             if (loop.is_contour) {
-                eloop->make_counter_clockwise();
+                if (eloop->is_clockwise())
+                    eloop->reverse_loop();
                 out.append(std::move(children.entities));
                 out.entities.emplace_back(eloop);
             } else {
-                eloop->make_clockwise();
+                if (eloop->is_counter_clockwise())
+                    eloop->reverse_loop();
                 out.entities.emplace_back(eloop);
                 out.append(std::move(children.entities));
             }
@@ -603,10 +608,8 @@ static ExtrusionEntityCollection traverse_extrusions(const PerimeterGenerator::P
             if (extrusion->is_closed) {
                 ExtrusionLoop extrusion_loop(std::move(paths));
                 // Restore the orientation of the extrusion loop.
-                if (pg_extrusion.is_contour)
-                    extrusion_loop.make_counter_clockwise();
-                else
-                    extrusion_loop.make_clockwise();
+                if (pg_extrusion.is_contour == extrusion_loop.is_clockwise())
+                    extrusion_loop.reverse_loop();
 
                 for (auto it = std::next(extrusion_loop.paths.begin()); it != extrusion_loop.paths.end(); ++it) {
                     assert(it->polyline.points.size() >= 2);
@@ -960,11 +963,9 @@ std::tuple<std::vector<ExtrusionPaths>, Polygons> generate_extra_perimeters_over
 
                 if (perimeter_polygon.empty()) { // fill possible gaps of single extrusion width
                     Polygons shrinked = intersection(offset(prev, -0.3 * overhang_flow.scaled_spacing()), expanded_overhang_to_cover);
-                    if (!shrinked.empty()) {
+                    if (!shrinked.empty())
                         extrusion_paths_append(overhang_region, reconnect_polylines(perimeter, overhang_flow.scaled_spacing()),
-                                               ExtrusionRole::OverhangPerimeter, overhang_flow.mm3_per_mm(), overhang_flow.width(),
-                                               overhang_flow.height());
-                    }
+                                               ExtrusionAttributes{ ExtrusionRole::OverhangPerimeter, overhang_flow });
 
                     Polylines  fills;
                     ExPolygons gap = shrinked.empty() ? offset_ex(prev, overhang_flow.scaled_spacing() * 0.5) : to_expolygons(shrinked);
@@ -975,14 +976,12 @@ std::tuple<std::vector<ExtrusionPaths>, Polygons> generate_extra_perimeters_over
                     if (!fills.empty()) {
                         fills = intersection_pl(fills, shrinked_overhang_to_cover);
                         extrusion_paths_append(overhang_region, reconnect_polylines(fills, overhang_flow.scaled_spacing()),
-                                               ExtrusionRole::OverhangPerimeter, overhang_flow.mm3_per_mm(), overhang_flow.width(),
-                                               overhang_flow.height());
+                                               ExtrusionAttributes{ ExtrusionRole::OverhangPerimeter, overhang_flow });
                     }
                     break;
                 } else {
                     extrusion_paths_append(overhang_region, reconnect_polylines(perimeter, overhang_flow.scaled_spacing()),
-                                           ExtrusionRole::OverhangPerimeter, overhang_flow.mm3_per_mm(), overhang_flow.width(),
-                                           overhang_flow.height());
+                                           ExtrusionAttributes{ExtrusionRole::OverhangPerimeter, overhang_flow });
                 }
 
                 if (intersection(perimeter_polygon, real_overhang).empty()) { continuation_loops--; }

src/libslic3r/Point.cpp

@@ -47,14 +47,12 @@ Pointf3s transform(const Pointf3s& points, const Transform3d& t)
 
 void Point::rotate(double angle, const Point &center)
 {
-    double cur_x = (double)(*this)(0);
-    double cur_y = (double)(*this)(1);
+    Vec2d  cur = this->cast<double>();
     double s   = ::sin(angle);
     double c   = ::cos(angle);
-    double dx    = cur_x - (double)center(0);
-    double dy    = cur_y - (double)center(1);
-    (*this)(0) = (coord_t)round( (double)center(0) + c * dx - s * dy );
-    (*this)(1) = (coord_t)round( (double)center(1) + c * dy + s * dx );
+    auto   d   = cur - center.cast<double>();
+    this->x() = fast_round_up<coord_t>(center.x() + c * d.x() - s * d.y());
+    this->y() = fast_round_up<coord_t>(center.y() + s * d.x() + c * d.y());
 }
 
 bool has_duplicate_points(Points &&pts)

src/libslic3r/Point.hpp

@@ -166,11 +166,12 @@ public:
     Point(const Point &rhs) { *this = rhs; }
 	explicit Point(const Vec2d& rhs) : Vec2crd(coord_t(std::round(rhs.x())), coord_t(std::round(rhs.y()))) {}
 	// This constructor allows you to construct Point from Eigen expressions
+    // This constructor has to be implicit (non-explicit) to allow implicit conversion from Eigen expressions.
     template<typename OtherDerived>
     Point(const Eigen::MatrixBase<OtherDerived> &other) : Vec2crd(other) {}
     static Point new_scale(coordf_t x, coordf_t y) { return Point(coord_t(scale_(x)), coord_t(scale_(y))); }
-    static Point new_scale(const Vec2d &v) { return Point(coord_t(scale_(v.x())), coord_t(scale_(v.y()))); }
-    static Point new_scale(const Vec2f &v) { return Point(coord_t(scale_(v.x())), coord_t(scale_(v.y()))); }
+    template<typename OtherDerived>
+    static Point new_scale(const Eigen::MatrixBase<OtherDerived> &v) { return Point(coord_t(scale_(v.x())), coord_t(scale_(v.y()))); }
 
     // This method allows you to assign Eigen expressions to MyVectorType
     template<typename OtherDerived>

src/libslic3r/Polyline.cpp

@@ -146,8 +146,10 @@ void Polyline::split_at(const Point &point, Polyline* p1, Polyline* p2) const
     }
 
     if (this->points.front() == point) {
+        //FIXME why is p1 NOT empty as in the case above?
         *p1 = { point };
         *p2 = *this;
+        return;
     }
 
     auto  min_dist2    = std::numeric_limits<double>::max();

src/libslic3r/Preset.cpp

@@ -456,7 +456,8 @@ static std::vector<std::string> s_Preset_print_options {
     "ooze_prevention", "standby_temperature_delta", "interface_shells", "extrusion_width", "first_layer_extrusion_width",
     "perimeter_extrusion_width", "external_perimeter_extrusion_width", "infill_extrusion_width", "solid_infill_extrusion_width",
     "top_infill_extrusion_width", "support_material_extrusion_width", "infill_overlap", "infill_anchor", "infill_anchor_max", "bridge_flow_ratio",
-    "elefant_foot_compensation", "xy_size_compensation", "threads", "resolution", "gcode_resolution", "wipe_tower", "wipe_tower_x", "wipe_tower_y",
+    "elefant_foot_compensation", "xy_size_compensation", "threads", "resolution", "gcode_resolution", "arc_fitting", "arc_fitting_tolerance",
+    "wipe_tower", "wipe_tower_x", "wipe_tower_y",
     "wipe_tower_width", "wipe_tower_cone_angle", "wipe_tower_rotation_angle", "wipe_tower_brim_width", "wipe_tower_bridging", "single_extruder_multi_material_priming", "mmu_segmented_region_max_width",
     "mmu_segmented_region_interlocking_depth", "wipe_tower_extruder", "wipe_tower_no_sparse_layers", "wipe_tower_extra_spacing", "compatible_printers", "compatible_printers_condition", "inherits",
     "perimeter_generator", "wall_transition_length", "wall_transition_filter_deviation", "wall_transition_angle",

src/libslic3r/Print.cpp

@@ -921,8 +921,10 @@ void Print::process()
 
     tbb::parallel_for(tbb::blocked_range<size_t>(0, m_objects.size(), 1), [this](const tbb::blocked_range<size_t> &range) {
         for (size_t idx = range.begin(); idx < range.end(); ++idx) {
-            m_objects[idx]->generate_support_material();
-            m_objects[idx]->estimate_curled_extrusions();
+            PrintObject &obj = *m_objects[idx];
+            obj.generate_support_material();
+            obj.estimate_curled_extrusions();
+            obj.calculate_overhanging_perimeters();
         }
     }, tbb::simple_partitioner());
 
@@ -1009,7 +1011,7 @@ std::string Print::export_gcode(const std::string& path_template, GCodeProcessor
     this->set_status(90, message);
 
     // Create GCode on heap, it has quite a lot of data.
-    std::unique_ptr<GCode> gcode(new GCode);
+    std::unique_ptr<GCodeGenerator> gcode(new GCodeGenerator);
     gcode->do_export(this, path.c_str(), result, thumbnail_cb);
 
     if (m_conflict_result.has_value())
@@ -1125,13 +1127,15 @@ void Print::_make_skirt()
         }
         // Extrude the skirt loop.
         ExtrusionLoop eloop(elrSkirt);
-        eloop.paths.emplace_back(ExtrusionPath(
-            ExtrusionPath(
+        eloop.paths.emplace_back(
+            ExtrusionAttributes{
                 ExtrusionRole::Skirt,
-                (float)mm3_per_mm,         // this will be overridden at G-code export time
+                ExtrusionFlow{
+                    float(mm3_per_mm),        // this will be overridden at G-code export time
                     flow.width(),
-				(float)first_layer_height  // this will be overridden at G-code export time
-            )));
+                    float(first_layer_height) // this will be overridden at G-code export time
+                }
+            });
         eloop.paths.back().polyline = loop.split_at_first_point();
         m_skirt.append(eloop);
         if (m_config.min_skirt_length.value > 0) {
@@ -1637,8 +1641,8 @@ std::string PrintStatistics::finalize_output_path(const std::string &path_in) co
             }
 
 
-            ExtrusionPath path(ExtrusionRole::WipeTower, 0.0, 0.0, lh);
-            path.polyline = { minCorner, {maxCorner.x(), minCorner.y()}, maxCorner, {minCorner.x(), maxCorner.y()}, minCorner };
+            ExtrusionPath path({ minCorner, {maxCorner.x(), minCorner.y()}, maxCorner, {minCorner.x(), maxCorner.y()}, minCorner },
+                ExtrusionAttributes{ ExtrusionRole::WipeTower, ExtrusionFlow{ 0.0, 0.0, lh } });
             paths.push_back({ path });
 
             // We added the border, now add several parallel lines so we can detect an object that is fully inside the tower.

src/libslic3r/Print.hpp

@@ -29,7 +29,7 @@
 
 namespace Slic3r {
 
-class GCode;
+class GCodeGenerator;
 class Layer;
 class ModelObject;
 class Print;
@@ -67,7 +67,7 @@ enum PrintStep : unsigned int {
 
 enum PrintObjectStep : unsigned int {
     posSlice, posPerimeters, posPrepareInfill,
-    posInfill, posIroning, posSupportSpotsSearch, posSupportMaterial, posEstimateCurledExtrusions, posCount,
+    posInfill, posIroning, posSupportSpotsSearch, posSupportMaterial, posEstimateCurledExtrusions, posCalculateOverhangingPerimeters, posCount,
 };
 
 // A PrintRegion object represents a group of volumes to print
@@ -376,6 +376,7 @@ private:
     void generate_support_spots();
     void generate_support_material();
     void estimate_curled_extrusions();
+    void calculate_overhanging_perimeters();
 
     void slice_volumes();
     // Has any support (not counting the raft).
@@ -697,7 +698,7 @@ private:
     Polygons m_sequential_print_clearance_contours;
 
     // To allow GCode to set the Print's GCodeExport step status.
-    friend class GCode;
+    friend class GCodeGenerator;
     // To allow GCodeProcessor to emit warnings.
     friend class GCodeProcessor;
     // Allow PrintObject to access m_mutex and m_cancel_callback.

src/libslic3r/PrintConfig.cpp

@@ -34,6 +34,13 @@ static t_config_enum_names enum_names_from_keys_map(const t_config_enum_values &
     template<> const t_config_enum_values& ConfigOptionEnum<NAME>::get_enum_values() { return s_keys_map_##NAME; } \
     template<> const t_config_enum_names& ConfigOptionEnum<NAME>::get_enum_names() { return s_keys_names_##NAME; }
 
+static const t_config_enum_values s_keys_map_ArcFittingType {
+    { "disabled",       int(ArcFittingType::Disabled) },
+    { "emit_center",    int(ArcFittingType::EmitCenter) },
+    { "emit_radius",    int(ArcFittingType::EmitRadius) }
+};
+CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(ArcFittingType)
+
 static t_config_enum_values s_keys_map_PrinterTechnology {
     { "FFF",            ptFFF },
     { "SLA",            ptSLA }
@@ -397,6 +404,27 @@ void PrintConfigDef::init_fff_params()
 {
     ConfigOptionDef* def;
 
+    def = this->add("arc_fitting", coEnum);
+    def->label = L("Arc fitting");
+    def->tooltip = L("Enable this to get a G-code file which has G2 and G3 moves. "
+                     "And the fitting tolerance is same with resolution");
+    def->set_enum<ArcFittingType>({
+        { "disabled",       "Disabled" },
+        { "emit_center",    "Enabled: G2/3 I J" },
+        { "emit_radius",    "Enabled: G2/3 R" }
+    });
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionEnum<ArcFittingType>(ArcFittingType::Disabled));
+
+    def = this->add("arc_fitting_tolerance", coFloatOrPercent);
+    def->label = L("Arc fitting tolerance");
+    def->sidetext = L("mm or %");
+    def->tooltip = L("When using the arc_fitting option, allow the curve to deviate a cetain % from the collection of strait paths.\n"
+                     "Can be a mm value or a percentage of the current extrusion width.");
+    def->mode = comAdvanced;
+    def->min = 0;
+    def->set_default_value(new ConfigOptionFloatOrPercent(5, true));
+
     // Maximum extruder temperature, bumped to 1500 to support printing of glass.
     const int max_temp = 1500;
     def = this->add("avoid_crossing_curled_overhangs", coBool);

src/libslic3r/PrintConfig.hpp

@@ -30,6 +30,12 @@
 
 namespace Slic3r {
 
+enum class ArcFittingType {
+    Disabled,
+    EmitCenter,
+    EmitRadius,
+};
+
 enum GCodeFlavor : unsigned char {
     gcfRepRapSprinter, gcfRepRapFirmware, gcfRepetier, gcfTeacup, gcfMakerWare, gcfMarlinLegacy, gcfMarlinFirmware, gcfKlipper, gcfSailfish, gcfMach3, gcfMachinekit,
     gcfSmoothie, gcfNoExtrusion,
@@ -141,6 +147,7 @@ enum class GCodeThumbnailsFormat {
     template<> const t_config_enum_names& ConfigOptionEnum<NAME>::get_enum_names(); \
     template<> const t_config_enum_values& ConfigOptionEnum<NAME>::get_enum_values();
 
+CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(ArcFittingType)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(PrinterTechnology)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(GCodeFlavor)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(MachineLimitsUsage)
@@ -671,6 +678,8 @@ PRINT_CONFIG_CLASS_DEFINE(
 PRINT_CONFIG_CLASS_DEFINE(
     GCodeConfig,
 
+    ((ConfigOptionEnum<ArcFittingType>, arc_fitting))
+    ((ConfigOptionFloatOrPercent,      arc_fitting_tolerance))
     ((ConfigOptionBool,                autoemit_temperature_commands))
     ((ConfigOptionString,              before_layer_gcode))
     ((ConfigOptionString,              between_objects_gcode))

src/libslic3r/PrintObject.cpp

@@ -3,7 +3,9 @@
 #include "ExPolygon.hpp"
 #include "Exception.hpp"
 #include "Flow.hpp"
+#include "GCode/ExtrusionProcessor.hpp"
 #include "KDTreeIndirect.hpp"
+#include "Line.hpp"
 #include "Point.hpp"
 #include "Polygon.hpp"
 #include "Polyline.hpp"
@@ -533,6 +535,65 @@ void PrintObject::estimate_curled_extrusions()
     }
 }
 
+void PrintObject::calculate_overhanging_perimeters()
+{
+    if (this->set_started(posCalculateOverhangingPerimeters)) {
+        BOOST_LOG_TRIVIAL(debug) << "Calculating overhanging perimeters - start";
+        m_print->set_status(89, _u8L("Calculating overhanging perimeters"));
+        std::vector<unsigned int>               extruders;
+        std::unordered_set<const PrintRegion *> regions_with_dynamic_speeds;
+        for (const PrintRegion *pr : this->print()->m_print_regions) {
+            if (pr->config().enable_dynamic_overhang_speeds.getBool()) {
+                regions_with_dynamic_speeds.insert(pr);
+            }
+            extruders.clear();
+            pr->collect_object_printing_extruders(*this->print(), extruders);
+            auto cfg = this->print()->config();
+            if (std::any_of(extruders.begin(), extruders.end(),
+                            [&cfg](unsigned int extruder_id) { return cfg.enable_dynamic_fan_speeds.get_at(extruder_id); })) {
+                regions_with_dynamic_speeds.insert(pr);
+            }
+        }
+
+        if (!regions_with_dynamic_speeds.empty()) {
+            std::unordered_map<size_t, AABBTreeLines::LinesDistancer<CurledLine>> curled_lines;
+            std::unordered_map<size_t, AABBTreeLines::LinesDistancer<Linef>>      unscaled_polygons_lines;
+            for (const Layer *l : this->layers()) {
+                curled_lines[l->id()]            = AABBTreeLines::LinesDistancer<CurledLine>{l->curled_lines};
+                unscaled_polygons_lines[l->id()] = AABBTreeLines::LinesDistancer<Linef>{to_unscaled_linesf(l->lslices)};
+            }
+            curled_lines[size_t(-1)]            = {};
+            unscaled_polygons_lines[size_t(-1)] = {};
+
+            tbb::parallel_for(tbb::blocked_range<size_t>(0, m_layers.size()), [this, &curled_lines, &unscaled_polygons_lines,
+                                                                               &regions_with_dynamic_speeds](
+                                                                                  const tbb::blocked_range<size_t> &range) {
+                PRINT_OBJECT_TIME_LIMIT_MILLIS(PRINT_OBJECT_TIME_LIMIT_DEFAULT);
+                for (size_t layer_idx = range.begin(); layer_idx < range.end(); ++layer_idx) {
+                    auto l = m_layers[layer_idx];
+                    if (l->id() == 0) { // first layer, do not split
+                        continue;
+                    }
+                    for (LayerRegion *layer_region : l->regions()) {
+                        if (regions_with_dynamic_speeds.find(layer_region->m_region) == regions_with_dynamic_speeds.end()) {
+                            continue;
+                        }
+                        size_t prev_layer_id = l->lower_layer ? l->lower_layer->id() : size_t(-1);
+                        layer_region->m_perimeters =
+                            ExtrusionProcessor::calculate_and_split_overhanging_extrusions(&layer_region->m_perimeters,
+                                                                                           unscaled_polygons_lines[prev_layer_id],
+                                                                                           curled_lines[l->id()]);
+                    }
+                }
+            });
+
+            m_print->throw_if_canceled();
+            BOOST_LOG_TRIVIAL(debug) << "Calculating overhanging perimeters - end";
+        }
+        this->set_done(posCalculateOverhangingPerimeters);
+    }
+}
+
 std::pair<FillAdaptive::OctreePtr, FillAdaptive::OctreePtr> PrintObject::prepare_adaptive_infill_data(
     const std::vector<std::pair<const Surface *, float>> &surfaces_w_bottom_z) const
 {
@@ -644,7 +705,9 @@ bool PrintObject::invalidate_state_by_config_options(
             || opt_key == "first_layer_extrusion_width"
             || opt_key == "perimeter_extrusion_width"
             || opt_key == "infill_overlap"
-            || opt_key == "external_perimeters_first") {
+            || opt_key == "external_perimeters_first"
+            || opt_key == "arc_fitting"
+            || opt_key == "arc_fitting_tolerance") {
             steps.emplace_back(posPerimeters);
         } else if (
                opt_key == "gap_fill_enabled"
@@ -845,7 +908,7 @@ bool PrintObject::invalidate_step(PrintObjectStep step)
     
     // propagate to dependent steps
     if (step == posPerimeters) {
-		invalidated |= this->invalidate_steps({ posPrepareInfill, posInfill, posIroning,  posSupportSpotsSearch, posEstimateCurledExtrusions });
+		invalidated |= this->invalidate_steps({ posPrepareInfill, posInfill, posIroning,  posSupportSpotsSearch, posEstimateCurledExtrusions, posCalculateOverhangingPerimeters });
         invalidated |= m_print->invalidate_steps({ psSkirtBrim });
     } else if (step == posPrepareInfill) {
         invalidated |= this->invalidate_steps({ posInfill, posIroning, posSupportSpotsSearch});
@@ -854,7 +917,7 @@ bool PrintObject::invalidate_step(PrintObjectStep step)
         invalidated |= m_print->invalidate_steps({ psSkirtBrim });
     } else if (step == posSlice) {
         invalidated |= this->invalidate_steps({posPerimeters, posPrepareInfill, posInfill, posIroning, posSupportSpotsSearch,
-                                               posSupportMaterial, posEstimateCurledExtrusions});
+                                               posSupportMaterial, posEstimateCurledExtrusions, posCalculateOverhangingPerimeters});
         invalidated |= m_print->invalidate_steps({ psSkirtBrim });
         m_slicing_params.valid = false;
     } else if (step == posSupportMaterial) {

src/libslic3r/ShortestPath.cpp

@@ -1006,16 +1006,20 @@ std::vector<std::pair<size_t, bool>> chain_segments_greedy2(SegmentEndPointFunc
 	return chain_segments_greedy_constrained_reversals2_<PointType, SegmentEndPointFunc, false, decltype(could_reverse_func)>(end_point_func, could_reverse_func, num_segments, start_near);
 }
 
-std::vector<std::pair<size_t, bool>> chain_extrusion_entities(std::vector<ExtrusionEntity*> &entities, const Point *start_near)
+std::vector<std::pair<size_t, bool>> chain_extrusion_entities(const std::vector<ExtrusionEntity*> &entities, const Point *start_near, const bool reversed)
 {
-	auto segment_end_point = [&entities](size_t idx, bool first_point) -> const Point& { return first_point ? entities[idx]->first_point() : entities[idx]->last_point(); };
+	auto segment_end_point = [&entities, reversed](size_t idx, bool first_point) -> const Point& { return first_point == reversed ? entities[idx]->last_point() : entities[idx]->first_point(); };
 	auto could_reverse 	   = [&entities](size_t idx) { const ExtrusionEntity *ee = entities[idx]; return ee->is_loop() || ee->can_reverse(); };
-	std::vector<std::pair<size_t, bool>> out = chain_segments_greedy_constrained_reversals<Point, decltype(segment_end_point), decltype(could_reverse)>(segment_end_point, could_reverse, entities.size(), start_near);
+	std::vector<std::pair<size_t, bool>> out = chain_segments_greedy_constrained_reversals<Point, decltype(segment_end_point), decltype(could_reverse)>(
+		segment_end_point, could_reverse, entities.size(), start_near);
 	for (std::pair<size_t, bool> &segment : out) {
 		ExtrusionEntity *ee = entities[segment.first];
 		if (ee->is_loop())
 			// Ignore reversals for loops, as the start point equals the end point.
 			segment.second = false;
+		else if (reversed)
+			// Input was already reversed.
+			segment.second = ! segment.second;
 		// Is can_reverse() respected by the reversals?
 		assert(ee->can_reverse() || ! segment.second);
 	}
@@ -1041,6 +1045,33 @@ void chain_and_reorder_extrusion_entities(std::vector<ExtrusionEntity*> &entitie
 	reorder_extrusion_entities(entities, chain_extrusion_entities(entities, start_near));
 }
 
+ExtrusionEntityReferences chain_extrusion_references(const std::vector<ExtrusionEntity*> &entities, const Point *start_near, const bool reversed)
+{
+	const std::vector<std::pair<size_t, bool>> chain = chain_extrusion_entities(entities, start_near, reversed);
+	ExtrusionEntityReferences out;
+	out.reserve(chain.size());
+    for (const std::pair<size_t, bool> &idx : chain) {
+		assert(entities[idx.first] != nullptr);
+        out.push_back({ *entities[idx.first], idx.second });
+    }
+    return out;
+}
+
+ExtrusionEntityReferences chain_extrusion_references(const ExtrusionEntityCollection &eec, const Point *start_near, const bool reversed)
+{
+	if (eec.no_sort) {
+		ExtrusionEntityReferences out;
+		out.reserve(eec.entities.size());
+	    for (const ExtrusionEntity *ee : eec.entities) {
+			assert(ee != nullptr);
+			// Never reverse a loop.
+	        out.push_back({ *ee, ! ee->is_loop() && reversed });
+	    }
+		return out;
+	} else
+		return chain_extrusion_references(eec.entities, start_near, reversed);
+}
+
 std::vector<std::pair<size_t, bool>> chain_extrusion_paths(std::vector<ExtrusionPath> &extrusion_paths, const Point *start_near)
 {
 	auto segment_end_point = [&extrusion_paths](size_t idx, bool first_point) -> const Point& { return first_point ? extrusion_paths[idx].first_point() : extrusion_paths[idx].last_point(); };

src/libslic3r/ShortestPath.hpp

@@ -18,13 +18,25 @@ namespace Slic3r {
 class ExPolygon;
 using ExPolygons = std::vector<ExPolygon>;
 
+// Used by chain_expolygons()
 std::vector<size_t> 				 chain_points(const Points &points, Point *start_near = nullptr);
+// Used to give layer islands a print order.
 std::vector<size_t> 				 chain_expolygons(const ExPolygons &expolygons, Point *start_near = nullptr);
 
-std::vector<std::pair<size_t, bool>> chain_extrusion_entities(std::vector<ExtrusionEntity*> &entities, const Point *start_near = nullptr);
+// Chain extrusion entities by a shortest distance. Returns the ordered extrusions together with a "reverse" flag.
+// Set input "reversed" to true if the vector of "entities" is to be considered to be reversed once already.
+std::vector<std::pair<size_t, bool>> chain_extrusion_entities(const std::vector<ExtrusionEntity*> &entities, const Point *start_near = nullptr, const bool reversed = false);
+// Reorder & reverse extrusion entities in place based on the "chain" ordering.
 void                                 reorder_extrusion_entities(std::vector<ExtrusionEntity*> &entities, const std::vector<std::pair<size_t, bool>> &chain);
+// Reorder & reverse extrusion entities in place.
 void                                 chain_and_reorder_extrusion_entities(std::vector<ExtrusionEntity*> &entities, const Point *start_near = nullptr);
 
+// Chain extrusion entities by a shortest distance. Returns the ordered extrusions together with a "reverse" flag.
+// Set input "reversed" to true if the vector of "entities" is to be considered to be reversed.
+ExtrusionEntityReferences			 chain_extrusion_references(const std::vector<ExtrusionEntity*> &entities, const Point *start_near = nullptr, const bool reversed = false);
+// The same as above, respect eec.no_sort flag.
+ExtrusionEntityReferences			 chain_extrusion_references(const ExtrusionEntityCollection &eec, const Point *start_near = nullptr, const bool reversed = false);
+
 std::vector<std::pair<size_t, bool>> chain_extrusion_paths(std::vector<ExtrusionPath> &extrusion_paths, const Point *start_near = nullptr);
 void                                 reorder_extrusion_paths(std::vector<ExtrusionPath> &extrusion_paths, std::vector<std::pair<size_t, bool>> &chain);
 void                                 chain_and_reorder_extrusion_paths(std::vector<ExtrusionPath> &extrusion_paths, const Point *start_near = nullptr);

src/libslic3r/Support/SupportCommon.cpp

@@ -485,8 +485,7 @@ static inline void fill_expolygon_generate_paths(
     extrusion_entities_append_paths(
         dst,
         std::move(polylines),
-        role,
-        flow.mm3_per_mm(), flow.width(), flow.height());
+        { role, flow });
 }
 
 static inline void fill_expolygons_generate_paths(
@@ -644,7 +643,7 @@ static inline void tree_supports_generate_paths(
                 ExPolygons level2 = offset2_ex({ expoly }, -1.5 * flow.scaled_width(), 0.5 * flow.scaled_width());
                 if (level2.size() == 1) {
                     Polylines polylines;
-                    extrusion_entities_append_paths(eec->entities, draw_perimeters(expoly, clip_length), ExtrusionRole::SupportMaterial, flow.mm3_per_mm(), flow.width(), flow.height(),
+                    extrusion_entities_append_paths(eec->entities, draw_perimeters(expoly, clip_length), { ExtrusionRole::SupportMaterial, flow },
                         // Disable reversal of the path, always start with the anchor, always print CCW.
                         false);
                     expoly = level2.front();
@@ -750,7 +749,7 @@ static inline void tree_supports_generate_paths(
         }
 
         ExtrusionEntitiesPtr &out = eec ? eec->entities : dst;
-        extrusion_entities_append_paths(out, std::move(polylines), ExtrusionRole::SupportMaterial, flow.mm3_per_mm(), flow.width(), flow.height(), 
+        extrusion_entities_append_paths(out, std::move(polylines), { ExtrusionRole::SupportMaterial, flow },
             // Disable reversal of the path, always start with the anchor, always print CCW.
             false);
         if (eec) {
@@ -794,7 +793,7 @@ static inline void fill_expolygons_with_sheath_generate_paths(
             eec->no_sort = true;
         }
         ExtrusionEntitiesPtr &out = no_sort ? eec->entities : dst;
-        extrusion_entities_append_paths(out, draw_perimeters(expoly, clip_length), ExtrusionRole::SupportMaterial, flow.mm3_per_mm(), flow.width(), flow.height());
+        extrusion_entities_append_paths(out, draw_perimeters(expoly, clip_length), { ExtrusionRole::SupportMaterial, flow });
         // Fill in the rest.
         fill_expolygons_generate_paths(out, offset_ex(expoly, float(-0.4 * spacing)), filler, fill_params, density, role, flow);
         if (no_sort && ! eec->empty())
@@ -1106,7 +1105,7 @@ void LoopInterfaceProcessor::generate(SupportGeneratorLayerExtruded &top_contact
     extrusion_entities_append_paths(
         top_contact_layer.extrusions,
         std::move(loop_lines),
-        ExtrusionRole::SupportMaterialInterface, flow.mm3_per_mm(), flow.width(), flow.height());
+        { ExtrusionRole::SupportMaterialInterface, flow });
 }
 
 #ifdef SLIC3R_DEBUG
@@ -1148,24 +1147,19 @@ static void modulate_extrusion_by_overlapping_layers(
     ExtrusionPath *extrusion_path_template = dynamic_cast<ExtrusionPath*>(extrusions_in_out.front());
     assert(extrusion_path_template != nullptr);
     ExtrusionRole extrusion_role  = extrusion_path_template->role();
-    float         extrusion_width = extrusion_path_template->width;
+    float         extrusion_width = extrusion_path_template->width();
 
     struct ExtrusionPathFragment
     {
-        ExtrusionPathFragment() : mm3_per_mm(-1), width(-1), height(-1) {};
-        ExtrusionPathFragment(double mm3_per_mm, float width, float height) : mm3_per_mm(mm3_per_mm), width(width), height(height) {};
-
+        ExtrusionFlow   flow;
         Polylines       polylines;
-        double          mm3_per_mm;
-        float           width;
-        float           height;
     };
 
     // Split the extrusions by the overlapping layers, reduce their extrusion rate.
     // The last path_fragment is from this_layer.
     std::vector<ExtrusionPathFragment> path_fragments(
         n_overlapping_layers + 1, 
-        ExtrusionPathFragment(extrusion_path_template->mm3_per_mm, extrusion_path_template->width, extrusion_path_template->height));
+        ExtrusionPathFragment{ extrusion_path_template->attributes() });
     // Don't use it, it will be released.
     extrusion_path_template = nullptr;
 
@@ -1242,8 +1236,8 @@ static void modulate_extrusion_by_overlapping_layers(
         path_fragments.back().polylines = diff_pl(path_fragments.back().polylines, polygons_trimming);
         // Adjust the extrusion parameters for a reduced layer height and a non-bridging flow (nozzle_dmr = -1, does not matter).
         assert(this_layer.print_z > overlapping_layer.print_z);
-        frag.height = float(this_layer.print_z - overlapping_layer.print_z);
-        frag.mm3_per_mm = Flow(frag.width, frag.height, -1.f).mm3_per_mm();
+        frag.flow.height = float(this_layer.print_z - overlapping_layer.print_z);
+        frag.flow.mm3_per_mm = Flow(frag.flow.width, frag.flow.height, -1.f).mm3_per_mm();
 #ifdef SLIC3R_DEBUG
         svg.draw(frag.polylines, dbg_index_to_color(i_overlapping_layer), scale_(0.1));
 #endif /* SLIC3R_DEBUG */
@@ -1326,15 +1320,14 @@ static void modulate_extrusion_by_overlapping_layers(
             ExtrusionPath         *path = multipath.paths.empty() ? nullptr : &multipath.paths.back();
             if (path != nullptr) {
                 // Verify whether the path is compatible with the current fragment.
-                assert(this_layer.layer_type == SupporLayerType::BottomContact || path->height != frag.height || path->mm3_per_mm != frag.mm3_per_mm);
-                if (path->height != frag.height || path->mm3_per_mm != frag.mm3_per_mm) {
+                assert(this_layer.layer_type == SupporLayerType::BottomContact || path->height() != frag.flow.height || path->mm3_per_mm() != frag.flow.mm3_per_mm);
+                if (path->height() != frag.flow.height || path->mm3_per_mm() != frag.flow.mm3_per_mm)
                     path = nullptr;
-                }
                 // Merging with the previous path. This can only happen if the current layer was reduced by a base layer, which was split into a base and interface layer.
             }
             if (path == nullptr) {
                 // Allocate a new path.
-                multipath.paths.push_back(ExtrusionPath(extrusion_role, frag.mm3_per_mm, frag.width, frag.height));
+                multipath.paths.emplace_back(ExtrusionAttributes{ extrusion_role, frag.flow });
                 path = &multipath.paths.back();
             }
             // The Clipper library may flip the order of the clipped polylines arbitrarily.
@@ -1369,8 +1362,8 @@ static void modulate_extrusion_by_overlapping_layers(
     }
     // If there are any non-consumed fragments, add them separately.
     //FIXME this shall not happen, if the Clipper works as expected and all paths split to fragments could be re-connected.
-    for (auto it_fragment = path_fragments.begin(); it_fragment != path_fragments.end(); ++ it_fragment)
-        extrusion_entities_append_paths(extrusions_in_out, std::move(it_fragment->polylines), extrusion_role, it_fragment->mm3_per_mm, it_fragment->width, it_fragment->height);
+    for (ExtrusionPathFragment &fragment : path_fragments)
+        extrusion_entities_append_paths(extrusions_in_out, std::move(fragment.polylines), { extrusion_role, fragment.flow });
 }
 
 // Support layer that is covered by some form of dense interface.

src/libslic3r/Support/SupportMaterial.cpp

@@ -1023,7 +1023,7 @@ namespace SupportMaterialInternal {
         assert(expansion_scaled >= 0.f);
         for (const ExtrusionPath &ep : loop.paths)
             if (ep.role() == ExtrusionRole::OverhangPerimeter && ! ep.polyline.empty()) {
-                float exp = 0.5f * (float)scale_(ep.width) + expansion_scaled;
+                float exp = 0.5f * (float)scale_(ep.width()) + expansion_scaled;
                 if (ep.is_closed()) {
                     if (ep.size() >= 3) {
                         // This is a complete loop.

src/libslic3r/SupportSpotsGenerator.cpp

@@ -328,9 +328,9 @@ std::vector<ExtrusionLine> check_extrusion_entity_stability(const ExtrusionEntit
             return {};
         }
         const float                                    flow_width = get_flow_width(layer_region, entity->role());
-        std::vector<ExtendedPoint> annotated_points = estimate_points_properties<true, true, true, true>(entity->as_polyline().points,
-                                                                                                         prev_layer_boundary, flow_width,
-                                                                                                         params.bridge_distance);
+        std::vector<ExtrusionProcessor::ExtendedPoint> annotated_points =
+            ExtrusionProcessor::estimate_points_properties<true, true, true, true>(entity->as_polyline().points, prev_layer_boundary,
+                                                                                   flow_width, params.bridge_distance);
 
         std::vector<ExtrusionLine> lines_out;
         lines_out.reserve(annotated_points.size());
@@ -339,8 +339,8 @@ std::vector<ExtrusionLine> check_extrusion_entity_stability(const ExtrusionEntit
         std::optional<Vec2d> bridging_dir{};
 
         for (size_t i = 0; i < annotated_points.size(); ++i) {
-            ExtendedPoint &curr_point = annotated_points[i];
-            const ExtendedPoint &prev_point = i > 0 ? annotated_points[i - 1] : annotated_points[i];
+            ExtrusionProcessor::ExtendedPoint       &curr_point = annotated_points[i];
+            const ExtrusionProcessor::ExtendedPoint &prev_point = i > 0 ? annotated_points[i - 1] : annotated_points[i];
 
             SupportPointCause potential_cause = std::abs(curr_point.curvature) > 0.1 ? SupportPointCause::FloatingBridgeAnchor :
                                                                                        SupportPointCause::LongBridge;
@@ -382,17 +382,17 @@ std::vector<ExtrusionLine> check_extrusion_entity_stability(const ExtrusionEntit
 
         const float flow_width = get_flow_width(layer_region, entity->role());
         // Compute only unsigned distance - prev_layer_lines can contain unconnected paths, thus the sign of the distance is unreliable
-        std::vector<ExtendedPoint> annotated_points = estimate_points_properties<true, true, false, false>(entity->as_polyline().points,
-                                                                                                           prev_layer_lines, flow_width,
-                                                                                                           params.bridge_distance);
+        std::vector<ExtrusionProcessor::ExtendedPoint> annotated_points =
+            ExtrusionProcessor::estimate_points_properties<true, true, false, false>(entity->as_polyline().points, prev_layer_lines,
+                                                                                     flow_width, params.bridge_distance);
 
         std::vector<ExtrusionLine> lines_out;
         lines_out.reserve(annotated_points.size());
         float bridged_distance = annotated_points.front().position != annotated_points.back().position ? (params.bridge_distance + 1.0f) :
                                                                                                          0.0f;
         for (size_t i = 0; i < annotated_points.size(); ++i) {
-            ExtendedPoint       &curr_point = annotated_points[i];
-            const ExtendedPoint &prev_point = i > 0 ? annotated_points[i - 1] : annotated_points[i];
+            ExtrusionProcessor::ExtendedPoint       &curr_point = annotated_points[i];
+            const ExtrusionProcessor::ExtendedPoint &prev_point = i > 0 ? annotated_points[i - 1] : annotated_points[i];
             float                                    line_len   = (prev_point.position - curr_point.position).norm();
             ExtrusionLine line_out{prev_point.position.cast<float>(), curr_point.position.cast<float>(), line_len, entity};
 
@@ -1107,11 +1107,12 @@ void estimate_supports_malformations(SupportLayerPtrs &layers, float flow_width,
             Polygon  pol(pl.points);
             pol.make_counter_clockwise();
 
-            auto annotated_points = estimate_points_properties<true, true, false, false>(pol.points, prev_layer_lines, flow_width);
+            auto annotated_points = ExtrusionProcessor::estimate_points_properties<true, true, false, false>(pol.points, prev_layer_lines,
+                                                                                                             flow_width);
 
             for (size_t i = 0; i < annotated_points.size(); ++i) {
-                const ExtendedPoint &a = i > 0 ? annotated_points[i - 1] : annotated_points[i];
-                const ExtendedPoint &b = annotated_points[i];
+                const ExtrusionProcessor::ExtendedPoint &a = i > 0 ? annotated_points[i - 1] : annotated_points[i];
+                const ExtrusionProcessor::ExtendedPoint &b = annotated_points[i];
                 ExtrusionLine line_out{a.position.cast<float>(), b.position.cast<float>(), float((a.position - b.position).norm()),
                                        extrusion};
 
@@ -1182,11 +1183,13 @@ void estimate_malformations(LayerPtrs &layers, const Params &params)
                 Points extrusion_pts;
                 extrusion->collect_points(extrusion_pts);
                 float flow_width       = get_flow_width(layer_region, extrusion->role());
-                auto  annotated_points = estimate_points_properties<true, true, false, false>(extrusion_pts, prev_layer_lines, flow_width,
+                auto  annotated_points = ExtrusionProcessor::estimate_points_properties<true, true, false, false>(extrusion_pts,
+                                                                                                                 prev_layer_lines,
+                                                                                                                 flow_width,
                                                                                                                  params.bridge_distance);
                 for (size_t i = 0; i < annotated_points.size(); ++i) {
-                    const ExtendedPoint &a = i > 0 ? annotated_points[i - 1] : annotated_points[i];
-                    const ExtendedPoint &b = annotated_points[i];
+                    const ExtrusionProcessor::ExtendedPoint &a = i > 0 ? annotated_points[i - 1] : annotated_points[i];
+                    const ExtrusionProcessor::ExtendedPoint &b = annotated_points[i];
                     ExtrusionLine line_out{a.position.cast<float>(), b.position.cast<float>(), float((a.position - b.position).norm()),
                                            extrusion};
 
@@ -1196,7 +1199,8 @@ void estimate_malformations(LayerPtrs &layers, const Params &params)
                                                                                                         prev_layer_lines.get_line(bottom_line_idx);
 
                     // correctify the distance sign using slice polygons
-                    float sign = (prev_layer_boundary.distance_from_lines<true>(middle.cast<double>()) + 0.5f * flow_width) < 0.0f ? -1.0f : 1.0f;
+                    float sign = (prev_layer_boundary.distance_from_lines<true>(middle.cast<double>()) + 0.5f * flow_width) < 0.0f ? -1.0f :
+                                                                                                                                     1.0f;
 
                     line_out.curled_up_height = estimate_curled_up_height(middle_distance * sign, 0.5 * (a.curvature + b.curvature),
                                                                           l->height, flow_width, bottom_line.curled_up_height, params);

src/slic3r/GUI/3DScene.cpp

@@ -1442,8 +1442,8 @@ void _3DScene::extrusionentity_to_verts(const ExtrusionPath& extrusion_path, flo
     polyline.remove_duplicate_points();
     polyline.translate(copy);
     const Lines               lines = polyline.lines();
-    std::vector<double> widths(lines.size(), extrusion_path.width);
-    std::vector<double> heights(lines.size(), extrusion_path.height);
+    std::vector<double> widths(lines.size(), extrusion_path.width());
+    std::vector<double> heights(lines.size(), extrusion_path.height());
     thick_lines_to_verts(lines, widths, heights, false, print_z, geometry);
 }
 
@@ -1459,8 +1459,8 @@ void _3DScene::extrusionentity_to_verts(const ExtrusionLoop& extrusion_loop, flo
         polyline.translate(copy);
         const Lines lines_this = polyline.lines();
         append(lines, lines_this);
-        widths.insert(widths.end(), lines_this.size(), extrusion_path.width);
-        heights.insert(heights.end(), lines_this.size(), extrusion_path.height);
+        widths.insert(widths.end(), lines_this.size(), extrusion_path.width());
+        heights.insert(heights.end(), lines_this.size(), extrusion_path.height());
     }
     thick_lines_to_verts(lines, widths, heights, true, print_z, geometry);
 }
@@ -1477,8 +1477,8 @@ void _3DScene::extrusionentity_to_verts(const ExtrusionMultiPath& extrusion_mult
         polyline.translate(copy);
         const Lines lines_this = polyline.lines();
         append(lines, lines_this);
-        widths.insert(widths.end(), lines_this.size(), extrusion_path.width);
-        heights.insert(heights.end(), lines_this.size(), extrusion_path.height);
+        widths.insert(widths.end(), lines_this.size(), extrusion_path.width());
+        heights.insert(heights.end(), lines_this.size(), extrusion_path.height());
     }
     thick_lines_to_verts(lines, widths, heights, false, print_z, geometry);
 }

src/slic3r/GUI/ConfigManipulation.cpp

@@ -341,6 +341,9 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig* config)
     toggle_field("min_feature_size", have_arachne);
     toggle_field("min_bead_width", have_arachne);
     toggle_field("thin_walls", !have_arachne);
+
+    bool has_arc_fitting = config->opt_enum<ArcFittingType>("arc_fitting") != ArcFittingType::Disabled;
+    toggle_field("arc_fitting_tolerance", has_arc_fitting);
 }
 
 void ConfigManipulation::update_print_sla_config(DynamicPrintConfig* config, const bool is_global_config/* = false*/)

src/slic3r/GUI/Tab.cpp

@@ -7,7 +7,7 @@
 #include "libslic3r/Utils.hpp"
 #include "libslic3r/Model.hpp"
 #include "libslic3r/GCode/GCodeProcessor.hpp"
-#include "libslic3r/GCodeWriter.hpp"
+#include "libslic3r/GCode/GCodeWriter.hpp"
 
 #include "slic3r/Utils/Http.hpp"
 #include "slic3r/Utils/PrintHost.hpp"
@@ -1649,6 +1649,8 @@ void TabPrint::build()
         optgroup->append_single_option_line("slicing_mode");
         optgroup->append_single_option_line("resolution");
         optgroup->append_single_option_line("gcode_resolution");
+        optgroup->append_single_option_line("arc_fitting");
+        optgroup->append_single_option_line("arc_fitting_tolerance");
         optgroup->append_single_option_line("xy_size_compensation");
         optgroup->append_single_option_line("elefant_foot_compensation", "elephant-foot-compensation_114487");
 

t/geometry.t

@@ -1,95 +0,0 @@
-use Test::More;
-use strict;
-use warnings;
-
-plan tests => 10;
-
-BEGIN {
-    use FindBin;
-    use lib "$FindBin::Bin/../lib";
-    use local::lib "$FindBin::Bin/../local-lib";
-}
-
-use Slic3r;
-use Slic3r::Geometry qw(PI
-    chained_path_from epsilon scale);
-
-{
-    # this test was failing on Windows (GH #1950)
-    my $polygon = Slic3r::Polygon->new(
-        [207802834,-57084522],[196528149,-37556190],[173626821,-25420928],[171285751,-21366123],
-        [118673592,-21366123],[116332562,-25420928],[93431208,-37556191],[82156517,-57084523],
-        [129714478,-84542120],[160244873,-84542120],
-    );
-    my $point = Slic3r::Point->new(95706562, -57294774);
-    ok $polygon->contains_point($point), 'contains_point';
-}
-
-#==========================================================
-
-my $polygons = [
-    Slic3r::Polygon->new( # contour, ccw
-        [45919000, 515273900], [14726100, 461246400], [14726100, 348753500], [33988700, 315389800], 
-        [43749700, 343843000], [45422300, 352251500], [52362100, 362637800], [62748400, 369577600], 
-        [75000000, 372014700], [87251500, 369577600], [97637800, 362637800], [104577600, 352251500], 
-        [107014700, 340000000], [104577600, 327748400], [97637800, 317362100], [87251500, 310422300], 
-        [82789200, 309534700], [69846100, 294726100], [254081000, 294726100], [285273900, 348753500], 
-        [285273900, 461246400], [254081000, 515273900],
-
-    ),
-    Slic3r::Polygon->new( # hole, cw
-        [75000000, 502014700], [87251500, 499577600], [97637800, 492637800], [104577600, 482251500], 
-        [107014700, 470000000], [104577600, 457748400], [97637800, 447362100], [87251500, 440422300], 
-        [75000000, 437985300], [62748400, 440422300], [52362100, 447362100], [45422300, 457748400], 
-        [42985300, 470000000], [45422300, 482251500], [52362100, 492637800], [62748400, 499577600],
-    ),
-];
-
-
-#==========================================================
-
-{
-    my $polygon = Slic3r::Polygon->new([0, 0], [10, 0], [5, 5]);
-    my $result = $polygon->split_at_index(1);
-    is ref($result), 'Slic3r::Polyline', 'split_at_index returns polyline';
-    is_deeply $result->pp, [ [10, 0], [5, 5], [0, 0], [10, 0] ], 'split_at_index';
-}
-
-#==========================================================
-
-#{
-#    my $bb = Slic3r::Geometry::BoundingBox->new_from_points([ map Slic3r::Point->new(@$_), [0, 1], [10, 2], [20, 2] ]);
-#    $bb->scale(2);
-#    is_deeply [ $bb->min_point->pp, $bb->max_point->pp ], [ [0,2], [40,4] ], 'bounding box is scaled correctly';
-#}
-
-#==========================================================
-
-{
-    # if chained_path() works correctly, these points should be joined with no diagonal paths
-    # (thus 26 units long)
-    my @points = map Slic3r::Point->new_scale(@$_), [26,26],[52,26],[0,26],[26,52],[26,0],[0,52],[52,52],[52,0];
-    my @ordered = @points[@{chained_path_from(\@points, $points[0])}];
-    ok !(grep { abs($ordered[$_]->distance_to($ordered[$_+1]) - scale 26) > epsilon } 0..$#ordered-1), 'chained_path';
-}
-
-#==========================================================
-
-{
-    my $line = Slic3r::Line->new([0, 0], [20, 0]);
-    is +Slic3r::Point->new(10, 10)->distance_to_line($line), 10, 'distance_to';
-    is +Slic3r::Point->new(50, 0)->distance_to_line($line), 30, 'distance_to';
-    is +Slic3r::Point->new(0, 0)->distance_to_line($line), 0, 'distance_to';
-    is +Slic3r::Point->new(20, 0)->distance_to_line($line), 0, 'distance_to';
-    is +Slic3r::Point->new(10, 0)->distance_to_line($line), 0, 'distance_to';
-}
-
-{
-    my $triangle = Slic3r::Polygon->new(
-        [16000170,26257364], [714223,461012], [31286371,461008],
-    );
-    my $simplified = $triangle->simplify(250000)->[0];
-    is scalar(@$simplified), 3, 'triangle is never simplified to less than 3 points';
-}
-
-__END__

tests/fff_print/test_cooling.cpp

@@ -14,7 +14,7 @@
 using namespace Slic3r;
 
 std::unique_ptr<CoolingBuffer> make_cooling_buffer(
-    GCode                           &gcode,
+    GCodeGenerator                  &gcode,
     const DynamicPrintConfig        &config         = DynamicPrintConfig{}, 
     const std::vector<unsigned int> &extruder_ids   = { 0 })
 {
@@ -65,7 +65,7 @@ SCENARIO("Cooling unit tests", "[Cooling]") {
             const double print_time = 100. / (3000. / 60.);
             //FIXME slowdown_below_layer_time is rounded down significantly from 1.8s to 1s.
             config.set_deserialize_strict({ { "slowdown_below_layer_time", { int(print_time * 0.999) } } });
-            GCode gcodegen;
+            GCodeGenerator gcodegen;
             auto buffer = make_cooling_buffer(gcodegen, config);
             std::string gcode = buffer->process_layer("G1 F3000;_EXTRUDE_SET_SPEED\nG1 X100 E1", 0, true);
             bool speed_not_altered = gcode.find("F3000") != gcode.npos;
@@ -83,7 +83,7 @@ SCENARIO("Cooling unit tests", "[Cooling]") {
         // Print time of gcode.
         const double print_time = 50. / (2500. / 60.) + 100. / (3000. / 60.) + 4. / (400. / 60.);
         config.set_deserialize_strict({ { "slowdown_below_layer_time", { int(print_time * 1.001) } } });
-        GCode gcodegen;
+        GCodeGenerator gcodegen;
         auto buffer = make_cooling_buffer(gcodegen, config);
         std::string gcode = buffer->process_layer(gcode_src, 0, true);
         THEN("speed is altered when elapsed time is lower than slowdown threshold") {
@@ -106,7 +106,7 @@ SCENARIO("Cooling unit tests", "[Cooling]") {
                 { "fan_below_layer_time"      , int(print_time1 * 0.88) },
                 { "slowdown_below_layer_time" , int(print_time1 * 0.99) }
             });
-            GCode gcodegen;
+            GCodeGenerator gcodegen;
             auto buffer = make_cooling_buffer(gcodegen, config);
             std::string gcode = buffer->process_layer(gcode1, 0, true);
             bool fan_not_activated = gcode.find("M106") == gcode.npos;
@@ -119,7 +119,7 @@ SCENARIO("Cooling unit tests", "[Cooling]") {
             { "fan_below_layer_time",      { int(print_time2 + 1.), int(print_time2 + 1.) } },
             { "slowdown_below_layer_time", { int(print_time2 + 2.), int(print_time2 + 2.) } }
         });
-        GCode gcodegen;
+        GCodeGenerator gcodegen;
         auto buffer = make_cooling_buffer(gcodegen, config, { 0, 1 });
         std::string gcode = buffer->process_layer(gcode1 + "T1\nG1 X0 E1 F3000\n", 0, true);
         THEN("fan is activated for the 1st tool") {
@@ -134,7 +134,7 @@ SCENARIO("Cooling unit tests", "[Cooling]") {
     WHEN("G-code block 2") {
         THEN("slowdown is computed on all objects printing at the same Z") {
             config.set_deserialize_strict({ { "slowdown_below_layer_time", int(print_time2 * 0.99) } });
-            GCode gcodegen;
+            GCodeGenerator gcodegen;
             auto buffer = make_cooling_buffer(gcodegen, config);
             std::string gcode = buffer->process_layer(gcode2, 0, true);
             bool ok = gcode.find("F3000") != gcode.npos;
@@ -145,7 +145,7 @@ SCENARIO("Cooling unit tests", "[Cooling]") {
                 { "fan_below_layer_time",      int(print_time2 * 0.65) },
                 { "slowdown_below_layer_time", int(print_time2 * 0.7) }
             });
-            GCode gcodegen;
+            GCodeGenerator gcodegen;
             auto buffer = make_cooling_buffer(gcodegen, config);
             // use an elapsed time which is < the threshold but greater than it when summed twice
             std::string gcode = buffer->process_layer(gcode2, 0, true) + buffer->process_layer(gcode2, 1, true);
@@ -158,7 +158,7 @@ SCENARIO("Cooling unit tests", "[Cooling]") {
                 { "fan_below_layer_time",      int(print_time2 + 1) },
                 { "slowdown_below_layer_time", int(print_time2 + 1) }
             });
-            GCode gcodegen;
+            GCodeGenerator gcodegen;
             auto buffer = make_cooling_buffer(gcodegen, config);
             // use an elapsed time which is < the threshold but greater than it when summed twice
             std::string gcode = buffer->process_layer(gcode2, 0, true) + buffer->process_layer(gcode2, 1, true);

tests/fff_print/test_extrusion_entity.cpp

@@ -21,7 +21,7 @@ static inline Slic3r::Point random_point(float LO=-50, float HI=50)
 // build a sample extrusion entity collection with random start and end points.
 static Slic3r::ExtrusionPath random_path(size_t length = 20, float LO = -50, float HI = 50)
 {
-    ExtrusionPath t { ExtrusionRole::Perimeter, 1.0, 1.0, 1.0 };
+    ExtrusionPath t{ ExtrusionAttributes{ ExtrusionRole::Perimeter, ExtrusionFlow{ 1.0, 1.0, 1.0 } } };
     for (size_t j = 0; j < length; ++ j)
         t.polyline.append(random_point(LO, HI));
     return t;
@@ -37,9 +37,8 @@ static Slic3r::ExtrusionPaths random_paths(size_t count = 10, size_t length = 20
 
 SCENARIO("ExtrusionPath", "[ExtrusionEntity]") {
     GIVEN("Simple path") {
-        Slic3r::ExtrusionPath path{ ExtrusionRole::ExternalPerimeter };
-        path.polyline = { { 100, 100 }, { 200, 100 }, { 200, 200 } };
-        path.mm3_per_mm = 1.;
+        Slic3r::ExtrusionPath path{ { { 100, 100 }, { 200, 100 }, { 200, 200 } },
+            ExtrusionAttributes{ ExtrusionRole::ExternalPerimeter, ExtrusionFlow{ 1., -1.f, -1.f } } };
         THEN("first point") {
             REQUIRE(path.first_point() == path.polyline.front());
         }
@@ -52,10 +51,7 @@ SCENARIO("ExtrusionPath", "[ExtrusionEntity]") {
 
 static ExtrusionPath new_extrusion_path(const Polyline &polyline, ExtrusionRole role, double mm3_per_mm)
 {
-    ExtrusionPath path(role);
-    path.polyline = polyline;
-    path.mm3_per_mm = 1.;
-    return path;
+    return { polyline, ExtrusionAttributes{ role, ExtrusionFlow{ mm3_per_mm, -1.f, -1.f } } };
 }
 
 SCENARIO("ExtrusionLoop", "[ExtrusionEntity]") 
@@ -67,6 +63,7 @@ SCENARIO("ExtrusionLoop", "[ExtrusionEntity]")
         loop.paths.emplace_back(new_extrusion_path(square.split_at_first_point(), ExtrusionRole::ExternalPerimeter, 1.));
         THEN("polygon area") {
             REQUIRE(loop.polygon().area() == Approx(square.area()));
+            REQUIRE(loop.area() == Approx(square.area()));
         }
         THEN("loop length") {
             REQUIRE(loop.length() == Approx(square.length()));
@@ -110,6 +107,9 @@ SCENARIO("ExtrusionLoop", "[ExtrusionEntity]")
         loop.paths.emplace_back(new_extrusion_path(polyline1, ExtrusionRole::ExternalPerimeter, 1.));
         loop.paths.emplace_back(new_extrusion_path(polyline2, ExtrusionRole::OverhangPerimeter, 1.));
 
+        THEN("area") {
+            REQUIRE(loop.area() == Approx(loop.polygon().area()));
+        }
         double tot_len = polyline1.length() + polyline2.length();
         THEN("length") {
             REQUIRE(loop.length() == Approx(tot_len));
@@ -212,6 +212,9 @@ SCENARIO("ExtrusionLoop", "[ExtrusionEntity]")
         loop.paths.emplace_back(new_extrusion_path(polyline3, ExtrusionRole::ExternalPerimeter, 1.));
         loop.paths.emplace_back(new_extrusion_path(polyline4, ExtrusionRole::OverhangPerimeter, 1.));
         double len = loop.length();
+        THEN("area") {
+            REQUIRE(loop.area() == Approx(loop.polygon().area()));
+        }
         WHEN("splitting at vertex") {
             Point point(4821067, 9321068);
             if (! loop.split_at_vertex(point))
@@ -234,6 +237,9 @@ SCENARIO("ExtrusionLoop", "[ExtrusionEntity]")
             Polyline { { 15896783, 15868739 }, { 24842049, 12117558 }, { 33853238, 15801279 }, { 37591780, 24780128 }, { 37591780, 24844970 }, 
                        { 33853231, 33825297 }, { 24842049, 37509013 }, { 15896798, 33757841 }, { 12211841, 24812544 }, { 15896783, 15868739 } },
             ExtrusionRole::ExternalPerimeter, 1.));
+        THEN("area") {
+            REQUIRE(loop.area() == Approx(loop.polygon().area()));
+        }
         double len = loop.length();
         THEN("split_at() preserves total length") {
             loop.split_at({ 15896783, 15868739 }, false, 0);
@@ -378,23 +384,27 @@ TEST_CASE("ExtrusionEntityCollection: Chained path", "[ExtrusionEntity]") {
         REQUIRE(chained == test.chained);
         ExtrusionEntityCollection unchained_extrusions;
         extrusion_entities_append_paths(unchained_extrusions.entities, test.unchained,
-            ExtrusionRole::InternalInfill, 0., 0.4f, 0.3f);
+            ExtrusionAttributes{ ExtrusionRole::InternalInfill, ExtrusionFlow{ 0., 0.4f, 0.3f } });
         THEN("Chaining works") {
-            ExtrusionEntityCollection chained_extrusions = unchained_extrusions.chained_path_from(test.initial_point);
-            REQUIRE(chained_extrusions.entities.size() == test.chained.size());
-            for (size_t i = 0; i < chained_extrusions.entities.size(); ++ i) {
+            ExtrusionEntityReferences chained_extrusions = chain_extrusion_references(unchained_extrusions, &test.initial_point);
+            REQUIRE(chained_extrusions.size() == test.chained.size());
+            for (size_t i = 0; i < chained_extrusions.size(); ++ i) {
                 const Points &p1 = test.chained[i].points;
-                const Points &p2 = dynamic_cast<const ExtrusionPath*>(chained_extrusions.entities[i])->polyline.points;
+                Points        p2 = chained_extrusions[i].cast<ExtrusionPath>()->polyline.points;
+                if (chained_extrusions[i].flipped())
+                    std::reverse(p2.begin(), p2.end());
                 REQUIRE(p1 == p2);
             }
         }
         THEN("Chaining produces no change with no_sort") {
             unchained_extrusions.no_sort = true;
-            ExtrusionEntityCollection chained_extrusions = unchained_extrusions.chained_path_from(test.initial_point);
-            REQUIRE(chained_extrusions.entities.size() == test.unchained.size());
-            for (size_t i = 0; i < chained_extrusions.entities.size(); ++ i) {
+            ExtrusionEntityReferences chained_extrusions = chain_extrusion_references(unchained_extrusions, &test.initial_point);
+            REQUIRE(chained_extrusions.size() == test.unchained.size());
+            for (size_t i = 0; i < chained_extrusions.size(); ++ i) {
                 const Points &p1 = test.unchained[i].points;
-                const Points &p2 = dynamic_cast<const ExtrusionPath*>(chained_extrusions.entities[i])->polyline.points;
+                Points        p2 = chained_extrusions[i].cast<ExtrusionPath>()->polyline.points;
+                if (chained_extrusions[i].flipped())
+                    std::reverse(p2.begin(), p2.end());
                 REQUIRE(p1 == p2);
             }
         }

tests/fff_print/test_gcode.cpp

@@ -7,7 +7,7 @@
 using namespace Slic3r;
 
 SCENARIO("Origin manipulation", "[GCode]") {
-	Slic3r::GCode gcodegen;
+	Slic3r::GCodeGenerator gcodegen;
 	WHEN("set_origin to (10,0)") {
     	gcodegen.set_origin(Vec2d(10,0));
     	REQUIRE(gcodegen.origin() == Vec2d(10, 0));

tests/fff_print/test_gcodewriter.cpp

@@ -2,7 +2,7 @@
 
 #include <memory>
 
-#include "libslic3r/GCodeWriter.hpp"
+#include "libslic3r/GCode/GCodeWriter.hpp"
 
 using namespace Slic3r;
 

tests/libslic3r/CMakeLists.txt

@@ -6,6 +6,7 @@ add_executable(${_TEST_NAME}_tests
 	test_aabbindirect.cpp
 	test_kdtreeindirect.cpp
 	test_arachne.cpp
+	test_arc_welder.cpp
 	test_clipper_offset.cpp
 	test_clipper_utils.cpp
 	test_color.cpp

tests/libslic3r/test_arc_welder.cpp

@@ -0,0 +1,264 @@
+#include <catch2/catch.hpp>
+#include <test_utils.hpp>
+
+#include <libslic3r/Geometry/ArcWelder.hpp>
+#include <libslic3r/libslic3r.h>
+
+using namespace Slic3r;
+
+TEST_CASE("arc basics", "[ArcWelder]") {
+    using namespace Slic3r::Geometry;
+
+    WHEN("arc from { 2000.f, 1000.f } to { 1000.f, 2000.f }") {
+        Vec2f p1{ 2000.f, 1000.f };
+        Vec2f p2{ 1000.f, 2000.f };
+        float r{ 1000.f };
+        THEN("90 degrees arc, CCW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, r, true);
+            REQUIRE(is_approx(c, Vec2f{ 1000.f, 1000.f }));
+            REQUIRE(ArcWelder::arc_angle(p1, p2, r) == Approx(0.5 * M_PI));
+            REQUIRE(ArcWelder::arc_length(p1, p2, r) == Approx(r * 0.5 * M_PI).epsilon(0.001));
+        }
+        THEN("90 degrees arc, CW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, r, false);
+            REQUIRE(is_approx(c, Vec2f{ 2000.f, 2000.f }));
+        }
+        THEN("270 degrees arc, CCW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, - r, true);
+            REQUIRE(is_approx(c, Vec2f{ 2000.f, 2000.f }));
+            REQUIRE(ArcWelder::arc_angle(p1, p2, - r) == Approx(1.5 * M_PI));
+            REQUIRE(ArcWelder::arc_length(p1, p2, - r) == Approx(r * 1.5 * M_PI).epsilon(0.001));
+        }
+        THEN("270 degrees arc, CW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, - r, false);
+            REQUIRE(is_approx(c, Vec2f{ 1000.f, 1000.f }));
+        }
+    }
+    WHEN("arc from { 1707.11f, 1707.11f } to { 1000.f, 2000.f }") {
+        Vec2f p1{ 1707.11f, 1707.11f };
+        Vec2f p2{ 1000.f, 2000.f };
+        float r{ 1000.f };
+        Vec2f center1 = Vec2f{ 1000.f, 1000.f };
+        // Center on the other side of the CCW arch.
+        Vec2f center2 = center1 + 2. * (0.5 * (p1 + p2) - center1);
+        THEN("45 degrees arc, CCW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, r, true);
+            REQUIRE(is_approx(c, center1, 1.f));
+            REQUIRE(ArcWelder::arc_angle(p1, p2, r) == Approx(0.25 * M_PI));
+            REQUIRE(ArcWelder::arc_length(p1, p2, r) == Approx(r * 0.25 * M_PI).epsilon(0.001));
+        }
+        THEN("45 degrees arc, CW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, r, false);
+            REQUIRE(is_approx(c, center2, 1.f));
+        }
+        THEN("315 degrees arc, CCW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, - r, true);
+            REQUIRE(is_approx(c, center2, 1.f));
+            REQUIRE(ArcWelder::arc_angle(p1, p2, - r) == Approx((2. - 0.25) * M_PI));
+            REQUIRE(ArcWelder::arc_length(p1, p2, - r) == Approx(r * (2. - 0.25) * M_PI).epsilon(0.001));
+        }
+        THEN("315 degrees arc, CW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, - r, false);
+            REQUIRE(is_approx(c, center1, 1.f));
+        }
+    }
+    WHEN("arc from { 1866.f, 1500.f } to { 1000.f, 2000.f }") {
+        Vec2f p1{ 1866.f, 1500.f };
+        Vec2f p2{ 1000.f, 2000.f };
+        float r{ 1000.f };
+        Vec2f center1 = Vec2f{ 1000.f, 1000.f };
+        // Center on the other side of the CCW arch.
+        Vec2f center2 = center1 + 2. * (0.5 * (p1 + p2) - center1);
+        THEN("60 degrees arc, CCW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, r, true);
+            REQUIRE(is_approx(c, center1, 1.f));
+            REQUIRE(is_approx(ArcWelder::arc_angle(p1, p2, r), float(M_PI / 3.), 0.001f));
+            REQUIRE(ArcWelder::arc_length(p1, p2, r) == Approx(r * M_PI / 3.).epsilon(0.001));
+        }
+        THEN("60 degrees arc, CW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, r, false);
+            REQUIRE(is_approx(c, center2, 1.f));
+        }
+        THEN("300 degrees arc, CCW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, - r, true);
+            REQUIRE(is_approx(c, center2, 1.f));
+            REQUIRE(is_approx(ArcWelder::arc_angle(p1, p2, - r), float((2. - 1./3.) * M_PI), 0.001f));
+            REQUIRE(ArcWelder::arc_length(p1, p2, - r) == Approx(r * (2. - 1. / 3.) * M_PI).epsilon(0.001));
+        }
+        THEN("300 degrees arc, CW") {
+            Vec2f c = ArcWelder::arc_center(p1, p2, - r, false);
+            REQUIRE(is_approx(c, center1, 1.f));
+        }
+    }
+}
+
+TEST_CASE("arc discretization", "[ArcWelder]") {
+    using namespace Slic3r::Geometry;
+    WHEN("arc from { 2, 1 } to { 1, 2 }") {
+        const Point p1         = Point::new_scale(2., 1.);
+        const Point p2         = Point::new_scale(1., 2.);
+        const Point center     = Point::new_scale(1., 1.);
+        const float radius     = scaled<float>(1.);
+        const float resolution = scaled<float>(0.002);
+        auto test = [center, resolution, radius](const Point &p1, const Point &p2, const float r, const bool ccw) {
+            Vec2f  c = ArcWelder::arc_center(p1.cast<float>(), p2.cast<float>(), r, ccw);
+            REQUIRE((p1.cast<float>() - c).norm() == Approx(radius));
+            REQUIRE((c - center.cast<float>()).norm() == Approx(0.));
+            Points pts = ArcWelder::arc_discretize(p1, p2, r, ccw, resolution);
+            REQUIRE(pts.size() >= 2);
+            REQUIRE(pts.front() == p1);
+            REQUIRE(pts.back() == p2);
+            for (const Point &p : pts)
+                REQUIRE(std::abs((p.cast<double>() - c.cast<double>()).norm() - double(radius)) < double(resolution + SCALED_EPSILON));
+        };
+        THEN("90 degrees arc, CCW") {
+            test(p1, p2, radius, true);
+        }
+        THEN("270 degrees arc, CCW") {
+            test(p2, p1, - radius, true);
+        }
+        THEN("90 degrees arc, CW") {
+            test(p2, p1, radius, false);
+        }
+        THEN("270 degrees arc, CW") {
+            test(p1, p2, - radius, false);
+        }
+    }
+}
+
+TEST_CASE("arc fitting", "[ArcWelder]") {
+    using namespace Slic3r::Geometry;
+
+    WHEN("arc from { 2, 1 } to { 1, 2 }") {
+        const Point p1         = Point::new_scale(2., 1.);
+        const Point p2         = Point::new_scale(1., 2.);
+        const Point center     = Point::new_scale(1., 1.);
+        const float radius     = scaled<float>(1.);
+        const float resolution = scaled<float>(0.002);
+        auto test = [center, resolution](const Point &p1, const Point &p2, const float r, const bool ccw) {
+            Points pts = ArcWelder::arc_discretize(p1, p2, r, ccw, resolution);
+            ArcWelder::Path path = ArcWelder::fit_path(pts, resolution + SCALED_EPSILON, ArcWelder::default_scaled_resolution);
+            REQUIRE(path.size() == 2);
+            REQUIRE(path.front().point == p1);
+            REQUIRE(path.front().radius == 0.f);
+            REQUIRE(path.back().point == p2);
+            REQUIRE(path.back().radius == Approx(r));
+            REQUIRE(path.back().ccw() == ccw);
+        };
+        THEN("90 degrees arc, CCW is fitted") {
+            test(p1, p2, radius, true);
+        }
+        THEN("270 degrees arc, CCW is fitted") {
+            test(p2, p1, - radius, true);
+        }
+        THEN("90 degrees arc, CW is fitted") {
+            test(p2, p1, radius, false);
+        }
+        THEN("270 degrees arc, CW is fitted") {
+            test(p1, p2, - radius, false);
+        }
+    }
+
+    WHEN("arc from { 2, 1 } to { 1, 2 }, another arc from { 2, 1 } to { 0, 2 }, tangentially connected") {
+        const Point p1 = Point::new_scale(2., 1.);
+        const Point p2 = Point::new_scale(1., 2.);
+        const Point p3 = Point::new_scale(0., 3.);
+        const Point center1 = Point::new_scale(1., 1.);
+        const Point center2 = Point::new_scale(1., 3.);
+        const float radius = scaled<float>(1.);
+        const float resolution = scaled<float>(0.002);
+        auto test = [center1, center2, resolution](const Point &p1, const Point &p2, const Point &p3, const float r, const bool ccw) {
+            Points pts = ArcWelder::arc_discretize(p1, p2, r, ccw, resolution);
+            {
+                Points pts2 = ArcWelder::arc_discretize(p2, p3, - r, ! ccw, resolution);
+                REQUIRE(pts.back() == pts2.front());
+                pts.insert(pts.end(), std::next(pts2.begin()), pts2.end());
+            }
+            ArcWelder::Path path = ArcWelder::fit_path(pts, resolution + SCALED_EPSILON, ArcWelder::default_scaled_resolution);
+            REQUIRE(path.size() == 3);
+            REQUIRE(path.front().point == p1);
+            REQUIRE(path.front().radius == 0.f);
+            REQUIRE(path[1].point == p2);
+            REQUIRE(path[1].radius == Approx(r));
+            REQUIRE(path[1].ccw() == ccw);
+            REQUIRE(path.back().point == p3);
+            REQUIRE(path.back().radius == Approx(- r));
+            REQUIRE(path.back().ccw() == ! ccw);
+        };
+        THEN("90 degrees arches, CCW are fitted") {
+            test(p1, p2, p3, radius, true);
+        }
+        THEN("270 degrees arc, CCW is fitted") {
+            test(p3, p2, p1, -radius, true);
+        }
+        THEN("90 degrees arc, CW is fitted") {
+            test(p3, p2, p1, radius, false);
+        }
+        THEN("270 degrees arc, CW is fitted") {
+            test(p1, p2, p3, -radius, false);
+        }
+    }
+}
+
+TEST_CASE("arc wedge test", "[ArcWelder]") {
+    using namespace Slic3r::Geometry;
+
+    WHEN("test point inside wedge, arc from { 2, 1 } to { 1, 2 }") {
+        const int64_t s  = 1000000;
+        const Vec2i64 p1{ 2 * s, s };
+        const Vec2i64 p2{ s, 2 * s };
+        const Vec2i64 center{ s, s };
+        const int64_t radius{ s };
+        auto test = [center](
+            // Arc data
+            const Vec2i64 &p1, const Vec2i64 &p2, const int64_t r, const bool ccw,
+            // Test data
+            const Vec2i64 &ptest, const bool ptest_inside) {
+            const Vec2d c = ArcWelder::arc_center(p1.cast<double>(), p2.cast<double>(), double(r), ccw);
+            REQUIRE(is_approx(c, center.cast<double>()));
+            REQUIRE(ArcWelder::inside_arc_wedge(p1, p2, center, r > 0, ccw, ptest) == ptest_inside);
+            REQUIRE(ArcWelder::inside_arc_wedge(p1.cast<double>(), p2.cast<double>(), double(r), ccw, ptest.cast<double>()) == ptest_inside);
+        };
+        auto test_quadrants = [center, test](
+            // Arc data
+            const Vec2i64 &p1, const Vec2i64 &p2, const int64_t r, const bool ccw,
+            // Test data
+            const Vec2i64 &ptest1, const bool ptest_inside1,
+            const Vec2i64 &ptest2, const bool ptest_inside2, 
+            const Vec2i64 &ptest3, const bool ptest_inside3,
+            const Vec2i64 &ptest4, const bool ptest_inside4) {
+            test(p1, p2, r, ccw, ptest1 + center, ptest_inside1);
+            test(p1, p2, r, ccw, ptest2 + center, ptest_inside2);
+            test(p1, p2, r, ccw, ptest3 + center, ptest_inside3);
+            test(p1, p2, r, ccw, ptest4 + center, ptest_inside4);
+        };
+        THEN("90 degrees arc, CCW") {
+            test_quadrants(p1, p2, radius, true, 
+                Vec2i64{   s,   s }, true,
+                Vec2i64{   s, - s }, false,
+                Vec2i64{ - s,   s }, false,
+                Vec2i64{ - s, - s }, false);
+        }
+        THEN("270 degrees arc, CCW") {
+            test_quadrants(p2, p1, -radius, true,
+                Vec2i64{   s,   s }, false,
+                Vec2i64{   s, - s }, true,
+                Vec2i64{ - s,   s }, true,
+                Vec2i64{ - s, - s }, true);
+        }
+        THEN("90 degrees arc, CW") {
+            test_quadrants(p2, p1, radius, false,
+                Vec2i64{   s,   s }, true,
+                Vec2i64{   s, - s }, false,
+                Vec2i64{ - s,   s }, false,
+                Vec2i64{ - s, - s }, false);
+        }
+        THEN("270 degrees arc, CW") {
+            test_quadrants(p1, p2, -radius, false,
+                Vec2i64{   s,   s }, false,
+                Vec2i64{   s, - s }, true,
+                Vec2i64{ - s,   s }, true,
+                Vec2i64{ - s, - s }, true);
+        }
+    }
+}

tests/libslic3r/test_geometry.cpp

@@ -84,16 +84,16 @@ TEST_CASE("Line::perpendicular_to", "[Geometry]") {
 TEST_CASE("Polygon::contains works properly", "[Geometry]"){
    // this test was failing on Windows (GH #1950)
     Slic3r::Polygon polygon(Points({
-        Point(207802834,-57084522),
-        Point(196528149,-37556190),
-        Point(173626821,-25420928),
-        Point(171285751,-21366123),
-        Point(118673592,-21366123),
-        Point(116332562,-25420928),
-        Point(93431208,-37556191),
-        Point(82156517,-57084523),
-        Point(129714478,-84542120),
-        Point(160244873,-84542120)
+        {207802834,-57084522},
+        {196528149,-37556190},
+        {173626821,-25420928},
+        {171285751,-21366123},
+        {118673592,-21366123},
+        {116332562,-25420928},
+        {93431208,-37556191},
+        {82156517,-57084523},
+        {129714478,-84542120},
+        {160244873,-84542120}
     }));
     Point point(95706562, -57294774);
     REQUIRE(polygon.contains(point));
@@ -196,6 +196,41 @@ TEST_CASE("Offseting a line generates a polygon correctly", "[Geometry]"){
     REQUIRE(area.area() == Slic3r::Polygon(Points({Point(10,5),Point(20,5),Point(20,15),Point(10,15)})).area());
 }
 
+SCENARIO("Circle Fit, 3 points", "[Geometry]") {
+    WHEN("Three points make a circle") {
+        double s1 = scaled<double>(1.);
+        THEN("circle_center(): A center point { 0, 0 } is returned") {
+            Vec2d center = Geometry::circle_center(Vec2d{ s1, 0. }, Vec2d{ 0, s1 }, Vec2d{ -s1, 0. }, SCALED_EPSILON);
+            REQUIRE(is_approx(center, Vec2d(0, 0)));
+        }
+        THEN("circle_center(): A center point { 0, 0 } is returned for points in reverse") {
+            Vec2d center = Geometry::circle_center(Vec2d{ -s1, 0. }, Vec2d{ 0, s1 }, Vec2d{ s1, 0. }, SCALED_EPSILON);
+            REQUIRE(is_approx(center, Vec2d(0, 0)));
+        }
+        THEN("try_circle_center(): A center point { 0, 0 } is returned") {
+            std::optional<Vec2d> center = Geometry::try_circle_center(Vec2d{ s1, 0. }, Vec2d{ 0, s1 }, Vec2d{ -s1, 0. }, SCALED_EPSILON);
+            REQUIRE(center);
+            REQUIRE(is_approx(*center, Vec2d(0, 0)));
+        }
+        THEN("try_circle_center(): A center point { 0, 0 } is returned for points in reverse") {
+            std::optional<Vec2d> center = Geometry::try_circle_center(Vec2d{ -s1, 0. }, Vec2d{ 0, s1 }, Vec2d{ s1, 0. }, SCALED_EPSILON);
+            REQUIRE(center);
+            REQUIRE(is_approx(*center, Vec2d(0, 0)));
+        }
+    }
+    WHEN("Three points are collinear") {
+        double s1 = scaled<double>(1.);
+        THEN("circle_center(): A center point { 2, 0 } is returned") {
+            Vec2d center = Geometry::circle_center(Vec2d{ s1, 0. }, Vec2d{ 2. * s1, 0. }, Vec2d{ 3. * s1, 0. }, SCALED_EPSILON);
+            REQUIRE(is_approx(center, Vec2d(2. * s1, 0)));
+        }
+        THEN("try_circle_center(): Fails for collinear points") {
+            std::optional<Vec2d> center = Geometry::try_circle_center(Vec2d{ s1, 0. }, Vec2d{ 2. * s1, 0. }, Vec2d{ 3. * s1, 0. }, SCALED_EPSILON);
+            REQUIRE(! center);
+        }
+    }
+}
+
 SCENARIO("Circle Fit, TaubinFit with Newton's method", "[Geometry]") {
     GIVEN("A vector of Vec2ds arranged in a half-circle with approximately the same distance R from some point") {
         Vec2d expected_center(-6, 0);
@@ -310,6 +345,7 @@ SCENARIO("Path chaining", "[Geometry]") {
 	GIVEN("A path") {
 		Points points = { Point(26,26),Point(52,26),Point(0,26),Point(26,52),Point(26,0),Point(0,52),Point(52,52),Point(52,0) };
 		THEN("Chained with no diagonals (thus 26 units long)") {
+            // if chain_points() works correctly, these points should be joined with no diagonal paths
 			std::vector<Points::size_type> indices = chain_points(points);
 			for (Points::size_type i = 0; i + 1 < indices.size(); ++ i) {
 				double dist = (points.at(indices.at(i)).cast<double>() - points.at(indices.at(i+1)).cast<double>()).norm();

tests/libslic3r/test_polyline.cpp

@@ -5,6 +5,25 @@
 
 using namespace Slic3r;
 
+SCENARIO("Simplify polyne, template", "[Polyline]")
+{
+    Points polyline{ {0,0}, {1000,0}, {2000,0}, {2000,1000}, {2000,2000}, {1000,2000}, {0,2000}, {0,1000}, {0,0} };
+    WHEN("simplified with Douglas-Peucker with back inserter") {
+        Points out;
+        douglas_peucker<int64_t>(polyline.begin(), polyline.end(), std::back_inserter(out), 10, [](const Point &p) { return p; });
+        THEN("simplified correctly") {
+            REQUIRE(out == Points{ {0,0}, {2000,0}, {2000,2000}, {0,2000}, {0,0} });
+        }
+    }
+    WHEN("simplified with Douglas-Peucker in place") {
+        Points out{ polyline };
+        out.erase(douglas_peucker<int64_t>(out.begin(), out.end(), out.begin(), 10, [](const Point &p) { return p; }), out.end());
+        THEN("simplified correctly") {
+            REQUIRE(out == Points{ {0,0}, {2000,0}, {2000,2000}, {0,2000}, {0,0} });
+        }
+    }
+}
+
 SCENARIO("Simplify polyline", "[Polyline]")
 {
     GIVEN("polyline 1") {

xs/src/perlglue.cpp

@@ -4,7 +4,7 @@
 namespace Slic3r {
 
 REGISTER_CLASS(ExPolygon, "ExPolygon");
-REGISTER_CLASS(GCode, "GCode");
+REGISTER_CLASS(GCodeGenerator, "GCode");
 REGISTER_CLASS(Line, "Line");
 REGISTER_CLASS(Polygon, "Polygon");
 REGISTER_CLASS(Polyline, "Polyline");

xs/xsp/Geometry.xsp

@@ -20,15 +20,6 @@ convex_hull(points)
     OUTPUT:
         RETVAL
 
-std::vector<Points::size_type>
-chained_path_from(points, start_from)
-    Points      points
-    Point*      start_from
-    CODE:
-        RETVAL = chain_points(points, start_from);
-    OUTPUT:
-        RETVAL
-
 double
 rad2deg(angle)
     double      angle

xs/xsp/Polygon.xsp

@@ -19,7 +19,6 @@
     Lines lines();
     Clone<Polyline> split_at_vertex(Point* point)
         %code{% RETVAL = THIS->split_at_vertex(*point); %};
-    Clone<Polyline> split_at_index(int index);
     Clone<Polyline> split_at_first_point();
     double length();
     double area();