Add monotonous infill thanks to @bubnikv and @wavexx

also the rectilinear2.cpp rework that go along
use of monotonous in ironing
use of monotonous instead of rectilinear of "filled" in top & bottom
reduce gap fill area from rectilinearWGapFill to the area with no overlap
fix flatten(): don't put everything in a no_sort collection but correctly recreate the hierarchy of no_sort, sort, no_sort of collections.

src/libslic3r/ExtrusionEntityCollection.cpp

@@ -151,14 +151,13 @@ ExtrusionEntityCollection ExtrusionEntityCollection::flatten(bool preserve_order
 }
 void
 FlatenEntities::use(const ExtrusionEntityCollection &coll) {
-    if (coll.no_sort && preserve_ordering) {
+    if ((coll.no_sort || this->to_fill.no_sort) && preserve_ordering) {
         FlatenEntities unsortable(coll, preserve_ordering);
         for (const ExtrusionEntity* entity : coll.entities) {
             entity->visit(unsortable);
         }
         to_fill.append(std::move(unsortable.to_fill));
-    }
+    } else {
-    else {
         for (const ExtrusionEntity* entity : coll.entities) {
             entity->visit(*this);
         }

src/libslic3r/Fill/FillBase.cpp

@@ -32,6 +32,7 @@ Fill* Fill::new_from_type(const InfillPattern type)
     case ipGyroid:              return new FillGyroid();
     case ipRectilinear:         return new FillRectilinear2();
 //  case ipRectilinear:         return new FillRectilinear();
+    case ipMonotonous:          return new FillMonotonous();
     case ipRectilinearWGapFill: return new FillRectilinear2WGapFill();
     case ipScatteredRectilinear:return new FillScatteredRectilinear();
     case ipLine:                return new FillLine();
@@ -146,7 +147,11 @@ std::pair<float, Point> Fill::_infill_direction(const Surface *surface) const
 
 void Fill::fill_surface_extrusion(const Surface *surface, const FillParams &params, ExtrusionEntitiesPtr &out) const {
     //add overlap & call fill_surface
-    Polylines polylines = this->fill_surface(surface, params);
+    Polylines polylines;
+    try {
+        polylines = this->fill_surface(surface, params);
+    } catch (InfillFailedException&) {
+    }
     if (polylines.empty())
         return;
     // ensure it doesn't over or under-extrude
@@ -590,10 +595,11 @@ Fill::do_gap_fill(const ExPolygons &gapfill_areas, const FillParams &params, Ext
     //    offset2_ex(gapfill_areas, double(-max / 2), double(+max / 2)),
     //    true);
     ExPolygons gapfill_areas_collapsed = offset2_ex(gapfill_areas, double(-min / 2), double(+min / 2));
+    const double minarea = scale_(params.config->gap_fill_min_area.get_abs_value(params.flow->width) ) * params.flow->scaled_width();
     for (const ExPolygon &ex : gapfill_areas_collapsed) {
         //remove too small gaps that are too hard to fill.
         //ie one that are smaller than an extrusion with width of min and a length of max.
-        if (ex.area() > scale_(params.flow->nozzle_diameter)*scale_(params.flow->nozzle_diameter) * 2) {
+        if (ex.area() > minarea) {
             MedialAxis{ ex, params.flow->scaled_width() * 2, params.flow->scaled_width() / 5, coord_t(params.flow->height) }.build(polylines_gapfill);
         }
     }

src/libslic3r/Fill/FillBase.hpp

@@ -22,49 +22,46 @@ namespace Slic3r {
 class ExPolygon;
 class Surface;
 
+class InfillFailedException : public std::runtime_error {
+public:
+    InfillFailedException() : std::runtime_error("Infill failed") {}
+};
+
 struct FillParams
 {
-    FillParams() { 
-        memset(this, 0, sizeof(FillParams));
-        // Adjustment does not work.
-        dont_adjust = true;
-        flow_mult = 1.f;
-        fill_exactly = false;
-        role = erNone;
-        flow = NULL;
-        config = NULL;
-    }
-
     bool        full_infill() const { return density > 0.9999f && density < 1.0001f; }
 
     // Fill density, fraction in <0, 1>
-    float       density;
+    float       density     { 0.f };
 
     // Fill extruding flow multiplier, fraction in <0, 1>. Used by "over bridge compensation"
-    float       flow_mult;
+    float       flow_mult   { 1.0f };
 
     // Don't connect the fill lines around the inner perimeter.
-    bool        dont_connect;
+    bool        dont_connect{ false };
 
     // Don't adjust spacing to fill the space evenly.
-    bool        dont_adjust;
+    bool        dont_adjust { true };
+
+    // Monotonous infill - strictly left to right for better surface quality of top infills.
+    bool        monotonous  { false };
 
     // Try to extrude the exact amount of plastic to fill the volume requested
-    bool        fill_exactly;
+    bool        fill_exactly{ false };
 
     // For Honeycomb.
     // we were requested to complete each loop;
     // in this case we don't try to make more continuous paths
-    bool        complete;
+    bool        complete    { false };
 
     // if role == erNone or ERCustom, this method have to choose the best role itself, else it must use the argument's role.
-    ExtrusionRole role;
+    ExtrusionRole role      { erNone };
 
     //flow to use
-    Flow  const *flow;
+    Flow  const* flow       { nullptr };
 
     //full configuration for the region, to avoid copying every bit that is needed. Use this for process-specific parameters.
-    PrintRegionConfig const *config;
+    PrintRegionConfig const *config{ nullptr };
 };
 static_assert(IsTriviallyCopyable<FillParams>::value, "FillParams class is not POD (and it should be - see constructor).");
 

src/libslic3r/Fill/FillRectilinear2.hpp

@@ -15,7 +15,7 @@ class FillRectilinear2 : public Fill
 {
 public:
     virtual Fill* clone() const override { return new FillRectilinear2(*this); };
-    virtual ~FillRectilinear2() {}
+    virtual ~FillRectilinear2() = default;
     virtual void init_spacing(coordf_t spacing, const FillParams &params) override;
     virtual Polylines fill_surface(const Surface *surface, const FillParams &params) const override;
 
@@ -25,11 +25,20 @@ protected:
     bool fill_surface_by_lines(const Surface *surface, const FillParams &params, float angleBase, float pattern_shift, Polylines &polylines_out) const;
 };
 
+class FillMonotonous : public FillRectilinear2
+{
+public:
+    virtual Fill* clone() const { return new FillMonotonous(*this); };
+    virtual ~FillMonotonous() = default;
+    virtual Polylines fill_surface(const Surface * surface, const FillParams & params) const override;
+    virtual bool no_sort() const { return true; }
+};
+
 class FillGrid2 : public FillRectilinear2
 {
 public:
     virtual Fill* clone() const override { return new FillGrid2(*this); };
-    virtual ~FillGrid2() {}
+    virtual ~FillGrid2() = default;
     virtual Polylines fill_surface(const Surface *surface, const FillParams &params) const override;
 
 protected:
@@ -41,7 +50,7 @@ class FillTriangles : public FillRectilinear2
 {
 public:
     virtual Fill* clone() const override { return new FillTriangles(*this); };
-    virtual ~FillTriangles() {}
+    virtual ~FillTriangles() = default;
     virtual Polylines fill_surface(const Surface *surface, const FillParams &params) const override;
 
 protected:
@@ -53,7 +62,7 @@ class FillStars : public FillRectilinear2
 {
 public:
     virtual Fill* clone() const override { return new FillStars(*this); };
-    virtual ~FillStars() {}
+    virtual ~FillStars() = default;
     virtual Polylines fill_surface(const Surface *surface, const FillParams &params) const override;
 
 protected:
@@ -65,7 +74,7 @@ class FillCubic : public FillRectilinear2
 {
 public:
     virtual Fill* clone() const override { return new FillCubic(*this); };
-    virtual ~FillCubic() {}
+    virtual ~FillCubic() = default;
     virtual Polylines fill_surface(const Surface *surface, const FillParams &params) const override;
 
 protected:
@@ -78,7 +87,7 @@ class FillRectilinear2Peri : public FillRectilinear2
 public:
 
     virtual Fill* clone() const override { return new FillRectilinear2Peri(*this); };
-    virtual ~FillRectilinear2Peri() {}
+    virtual ~FillRectilinear2Peri() = default;
     //virtual Polylines fill_surface(const Surface *surface, const FillParams &params);
     virtual void fill_surface_extrusion(const Surface *surface, const FillParams &params, ExtrusionEntitiesPtr &out) const override;
 
@@ -89,7 +98,7 @@ class FillScatteredRectilinear : public FillRectilinear2
 {
 public:
     virtual Fill* clone() const override{ return new FillScatteredRectilinear(*this); };
-    virtual ~FillScatteredRectilinear() {}
+    virtual ~FillScatteredRectilinear() = default;
     virtual Polylines fill_surface(const Surface *surface, const FillParams &params) const override;
 
 protected:
@@ -102,7 +111,7 @@ class FillRectilinearSawtooth : public FillRectilinear2 {
 public:
 
     virtual Fill* clone() const override { return new FillRectilinearSawtooth(*this); };
-    virtual ~FillRectilinearSawtooth() {}
+    virtual ~FillRectilinearSawtooth() = default;
     virtual void fill_surface_extrusion(const Surface *surface, const FillParams &params, ExtrusionEntitiesPtr &out) const override;
 
 };
@@ -112,7 +121,7 @@ class FillRectilinear2WGapFill : public FillRectilinear2
 public:
 
     virtual Fill* clone() const { return new FillRectilinear2WGapFill(*this); };
-    virtual ~FillRectilinear2WGapFill() {}
+    virtual ~FillRectilinear2WGapFill() = default;
     virtual void fill_surface_extrusion(const Surface *surface, const FillParams &params, ExtrusionEntitiesPtr &out) const override;
     static void split_polygon_gap_fill(const Surface &surface, const FillParams &params, ExPolygons &rectilinear, ExPolygons &gapfill);
 };

src/libslic3r/Fill/FillSmooth.cpp

@@ -24,7 +24,7 @@ namespace Slic3r {
         
         // Save into layer smoothing path.
         ExtrusionEntityCollection *eec = new ExtrusionEntityCollection();
-        eec->no_sort = false;
+        eec->no_sort = params.monotonous;
         FillParams params_modifided = params;
         if (params.config != NULL && idx > 0) params_modifided.density /= (float)params.config->fill_smooth_width.get_abs_value(1);
         else if (params.config != NULL && idx == 0) params_modifided.density *= 1;
@@ -133,14 +133,18 @@ namespace Slic3r {
         // first infill
         perform_single_fill(0, *eecroot, *surface, params, volumeToOccupy);
 
+        //use monotonous for ironing pass
+        FillParams monotonous_params = params;
+        monotonous_params.monotonous = true;
+
         //second infill
         if (nbPass > 1){
-            perform_single_fill(1, *eecroot, *surface, params, volumeToOccupy);
+            perform_single_fill(1, *eecroot, *surface, monotonous_params, volumeToOccupy);
         }
 
         // third infill
         if (nbPass > 2){
-            perform_single_fill(2, *eecroot, *surface, params, volumeToOccupy);
+            perform_single_fill(2, *eecroot, *surface, monotonous_params, volumeToOccupy);
         }
         
         if (!eecroot->entities.empty()) 

src/libslic3r/GCode.cpp

@@ -4501,6 +4501,7 @@ void GCode::ObjectByExtruder::Island::Region::append(const Type type, const Extr
 
     // First we append the entities, there are eec->entities.size() of them:
     //don't do fill->entities because it will discard no_sort, we must use flatten(preserve_ordering = true)
+    // this method will encapsulate every no_sort into an other collection, so we can get the entities directly.
     ExtrusionEntitiesPtr entities = eec->flatten(true).entities;
     size_t old_size = perimeters_or_infills->size();
     size_t new_size = old_size + entities.size();

src/libslic3r/PrintConfig.cpp

@@ -597,6 +597,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_keys_map = &ConfigOptionEnum<InfillPattern>::get_enum_values();
     def->enum_values.push_back("rectilinear");
     def->enum_values.push_back("rectilineargapfill");
+    def->enum_values.push_back("monotonous");
     def->enum_values.push_back("concentric");
     def->enum_values.push_back("concentricgapfill");
     def->enum_values.push_back("hilbertcurve");
@@ -607,7 +608,8 @@ void PrintConfigDef::init_fff_params()
     def->enum_values.push_back("smoothtriple");
     def->enum_values.push_back("smoothhilbert");
     def->enum_labels.push_back(L("Rectilinear"));
-    def->enum_labels.push_back(L("Rectilinear (filled)"));
+    def->enum_labels.push_back(L("Monotonous (filled)"));
+    def->enum_labels.push_back(L("Monotonous"));
     def->enum_labels.push_back(L("Concentric"));
     def->enum_labels.push_back(L("Concentric (filled)"));
     def->enum_labels.push_back(L("Hilbert Curve"));
@@ -615,7 +617,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_labels.push_back(L("Octagram Spiral"));
     def->enum_labels.push_back(L("Sawtooth"));
     def->enum_labels.push_back(L("Ironing"));
-    def->set_default_value(new ConfigOptionEnum<InfillPattern>(ipRectilinear));
+    def->set_default_value(new ConfigOptionEnum<InfillPattern>(ipMonotonous));
 
     def = this->add("bottom_fill_pattern", coEnum);
     def->label = L("Bottom");
@@ -627,6 +629,7 @@ void PrintConfigDef::init_fff_params()
 
     def->enum_values.push_back("rectilinear");
     def->enum_values.push_back("rectilineargapfill");
+    def->enum_values.push_back("monotonous");
     def->enum_values.push_back("concentric");
     def->enum_values.push_back("concentricgapfill");
     def->enum_values.push_back("hilbertcurve");
@@ -634,7 +637,8 @@ void PrintConfigDef::init_fff_params()
     def->enum_values.push_back("octagramspiral");
     def->enum_values.push_back("smooth");
     def->enum_labels.push_back(L("Rectilinear"));
-    def->enum_labels.push_back(L("Rectilinear (filled)"));
+    def->enum_labels.push_back(L("Monotonous (filled)"));
+    def->enum_labels.push_back(L("Monotonous"));
     def->enum_labels.push_back(L("Concentric"));
     def->enum_labels.push_back(L("Concentric (filled)"));
     def->enum_labels.push_back(L("Hilbert Curve"));
@@ -642,7 +646,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_labels.push_back(L("Octagram Spiral"));
     def->enum_labels.push_back(L("Ironing"));
     def->mode = comAdvanced;
-    def->set_default_value(new ConfigOptionEnum<InfillPattern>(ipRectilinear));
+    def->set_default_value(new ConfigOptionEnum<InfillPattern>(ipMonotonous));
 
     def = this->add("solid_fill_pattern", coEnum);
     def->label = L("Solid pattern");
@@ -653,6 +657,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_values.push_back("smooth");
     def->enum_values.push_back("rectilinear");
     def->enum_values.push_back("rectilineargapfill");
+    def->enum_values.push_back("monotonous");
     def->enum_values.push_back("concentric");
     def->enum_values.push_back("concentricgapfill");
     def->enum_values.push_back("hilbertcurve");
@@ -661,6 +666,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_labels.push_back(L("Ironing"));
     def->enum_labels.push_back(L("Rectilinear"));
     def->enum_labels.push_back(L("Rectilinear (filled)"));
+    def->enum_labels.push_back(L("Monotonous"));
     def->enum_labels.push_back(L("Concentric"));
     def->enum_labels.push_back(L("Concentric (filled)"));
     def->enum_labels.push_back(L("Hilbert Curve"));
@@ -1410,6 +1416,7 @@ void PrintConfigDef::init_fff_params()
     def->tooltip = L("Fill pattern for general low-density infill.");
     def->enum_keys_map = &ConfigOptionEnum<InfillPattern>::get_enum_values();
     def->enum_values.push_back("rectilinear");
+    def->enum_values.push_back("monotonous");
     def->enum_values.push_back("grid");
     def->enum_values.push_back("triangles");
     def->enum_values.push_back("stars");
@@ -1424,6 +1431,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_values.push_back("octagramspiral");
     def->enum_values.push_back("scatteredrectilinear"); 
     def->enum_labels.push_back(L("Rectilinear"));
+    def->enum_labels.push_back(L("Monotonous"));
     def->enum_labels.push_back(L("Grid"));
     def->enum_labels.push_back(L("Triangles"));
     def->enum_labels.push_back(L("Stars"));
@@ -3136,12 +3144,14 @@ void PrintConfigDef::init_fff_params()
     def->tooltip = L("Pattern for interface layer.");
     def->enum_keys_map = &ConfigOptionEnum<InfillPattern>::get_enum_values();
     def->enum_values.push_back("rectilinear");
+    def->enum_values.push_back("monotonous");
     def->enum_values.push_back("concentric");
     def->enum_values.push_back("concentricgapfill");
     def->enum_values.push_back("hilbertcurve");
     def->enum_values.push_back("sawtooth");
     def->enum_values.push_back("smooth");
     def->enum_labels.push_back(L("Rectilinear"));
+    def->enum_labels.push_back(L("Monotonous"));
     def->enum_labels.push_back(L("Concentric"));
     def->enum_labels.push_back(L("Concentric (filled)"));
     def->enum_labels.push_back(L("Hilbert Curve"));

src/libslic3r/PrintConfig.hpp

@@ -59,7 +59,9 @@ enum PrintHostType {
 enum InfillPattern {
     ipRectilinear, ipGrid, ipTriangles, ipStars, ipCubic, ipLine, ipConcentric, ipHoneycomb, ip3DHoneycomb,
     ipGyroid, ipHilbertCurve, ipArchimedeanChords, ipOctagramSpiral, ipSmooth, ipSmoothHilbert, ipSmoothTriple,
-    ipRectiWithPerimeter, ipConcentricGapFill, ipScatteredRectilinear, ipSawtooth, ipRectilinearWGapFill, ipCount
+    ipRectiWithPerimeter, ipConcentricGapFill, ipScatteredRectilinear, ipSawtooth, ipRectilinearWGapFill, 
+    ipMonotonous,
+    ipCount
 };
 
 enum SupportMaterialPattern {
@@ -165,6 +167,7 @@ template<> inline const t_config_enum_values& ConfigOptionEnum<InfillPattern>::g
     static t_config_enum_values keys_map;
     if (keys_map.empty()) {
         keys_map["rectilinear"]         = ipRectilinear;
+        keys_map["monotonous"]          = ipMonotonous;
         keys_map["grid"]                = ipGrid;
         keys_map["triangles"]           = ipTriangles;
         keys_map["stars"]               = ipStars;
@@ -182,8 +185,8 @@ template<> inline const t_config_enum_values& ConfigOptionEnum<InfillPattern>::g
         keys_map["smoothtriple"]        = ipSmoothTriple;
         keys_map["smoothhilbert"]       = ipSmoothHilbert;
         keys_map["rectiwithperimeter"]  = ipRectiWithPerimeter;
-        keys_map["scatteredrectilinear"] = ipScatteredRectilinear;
+        keys_map["scatteredrectilinear"]= ipScatteredRectilinear;
-        keys_map["rectilineargapfill"] = ipRectilinearWGapFill;
+        keys_map["rectilineargapfill"]  = ipRectilinearWGapFill;
         keys_map["sawtooth"]            = ipSawtooth;
     }
     return keys_map;

src/libslic3r/PrintObject.cpp

@@ -3351,6 +3351,7 @@ void PrintObject::combine_infill()
              // Because fill areas for rectilinear and honeycomb are grown 
              // later to overlap perimeters, we need to counteract that too.
                 ((region->config().fill_pattern == ipRectilinear   ||
+                  region->config().fill_pattern == ipMonotonous    ||
                   region->config().fill_pattern == ipGrid          ||
                   region->config().fill_pattern == ipLine          ||
                   region->config().fill_pattern == ipHoneycomb) ? 1.5f : 0.5f) * 

src/libslic3r/ShortestPath.cpp

@@ -58,6 +58,7 @@ std::vector<std::pair<size_t, bool>> chain_segments_closest_point(std::vector<En
 		EndPointType &end_point = end_points[next_idx];
 		//set the new entry point as taken
 		end_point.chain_id = 1;
+		assert((next_idx & 1) == 0 || could_reverse_func(next_idx >> 1));
 		out.emplace_back(next_idx / 2, (next_idx & 1) != 0);
 		//now switch to the other end of the segment
 		this_idx = next_idx ^ 1;

src/slic3r/GUI/Field.cpp

@@ -987,11 +987,9 @@ void Choice::set_value(const boost::any& value, bool change_event)
         int val = boost::any_cast<int>(value);
         if (m_opt_id == "top_fill_pattern" || m_opt_id == "bottom_fill_pattern" || m_opt_id == "solid_fill_pattern"
             || m_opt_id == "fill_pattern" || m_opt_id == "support_material_interface_pattern" || m_opt_id == "brim_ears_pattern")
-        {
             val = idx_from_enum_value<InfillPattern>(val);
-        } else if (m_opt_id.compare("perimeter_loop_seam") == 0) {
+        else if (m_opt_id.compare("perimeter_loop_seam") == 0)
             val = idx_from_enum_value<SeamPosition>(val);
-        }
         else if (m_opt_id.compare("complete_objects_sort") == 0)
             val = idx_from_enum_value<CompleteObjectSort>(val);
         else if (m_opt_id.compare("gcode_flavor") == 0)