thin walls: merge path into external perimeter loop when possible.

resources/ui_layout/print.ui

@@ -34,6 +34,7 @@ group:Quality
 		setting:thin_walls
 		setting:width$5:thin_walls_min_width
 		setting:width$5:thin_walls_overlap
+		setting:thin_walls_merge
 	end_line
 group:Overhangs
 	line:On perimeters

src/libslic3r/MedialAxis.cpp

@@ -1901,10 +1901,13 @@ thin_variable_width(const ThickPolylines &polylines, ExtrusionRole role, Flow fl
             if (paths.front().first_point().coincides_with(paths.back().last_point())) {
                 coll.append(ExtrusionLoop(paths));
             } else {
-                //not a loop : avoid to "sort" it.
-                ExtrusionEntityCollection unsortable_coll(paths);
-                unsortable_coll.no_sort = true;
-                coll.append(unsortable_coll);
+                if (role == erThinWall){
+                    //thin walls : avoid to cut them, please.
+                    ExtrusionEntityCollection unsortable_coll(paths);
+                    unsortable_coll.no_sort = true;
+                    coll.append(unsortable_coll);
+                }else //gap fill : cut them as much as you want
+                    coll.append(paths);
             }
         }
     }

src/libslic3r/PerimeterGenerator.cpp

@@ -717,7 +717,12 @@ void PerimeterGenerator::process()
                     thin_walls.clear();
                 }
             } else {
-                entities = this->_traverse_loops(contours.front(), thin_walls);
+                if (this->object_config->thin_walls_merge) {
+                    entities = this->_traverse_loops(contours.front(), ThickPolylines{});
+                    _merge_thin_walls(entities, thin_walls);
+                } else {
+                    entities = this->_traverse_loops(contours.front(), thin_walls);
+                }
             }
 
             
@@ -917,7 +922,6 @@ void PerimeterGenerator::process()
     } // for each island
 }
 
-
 ExtrusionEntityCollection PerimeterGenerator::_traverse_loops(
     const PerimeterGeneratorLoops &loops, ThickPolylines &thin_walls) const
 {
@@ -1056,6 +1060,170 @@ ExtrusionEntityCollection PerimeterGenerator::_traverse_loops(
     return coll_out;
 }
 
+void PerimeterGenerator::_merge_thin_walls(ExtrusionEntityCollection &extrusions, ThickPolylines &thin_walls) const {
+    class ChangeFlow : public ExtrusionVisitor {
+    public:
+        float percent_extrusion;
+        std::vector<ExtrusionPath> paths;
+        virtual void use(ExtrusionPath &path) override {
+            path.mm3_per_mm *= percent_extrusion;
+            path.width *= percent_extrusion;
+            paths.emplace_back(std::move(path));
+        }
+        virtual void use(ExtrusionPath3D &path3D) override { /*shouldn't happen*/ }
+        virtual void use(ExtrusionMultiPath &multipath) override { /*shouldn't happen*/ }
+        virtual void use(ExtrusionMultiPath3D &multipath) { /*shouldn't happen*/ }
+        virtual void use(ExtrusionLoop &loop) override {
+            for (ExtrusionPath &path : loop.paths)
+                this->use(path);
+        }
+        virtual void use(ExtrusionEntityCollection &collection) override {
+            for (ExtrusionEntity *entity : collection.entities)
+                entity->visit(*this);
+        }
+    };
+    struct BestPoint {
+        //Point p;
+        ExtrusionPath *path;
+        size_t idx_path;
+        ExtrusionLoop *loop;
+        size_t idx_line;
+        Line line;
+        double dist;
+        bool from_start;
+    };
+    //use a visitor to found the best point.
+    class SearchBestPoint : public ExtrusionVisitor {
+    public:
+        ThickPolyline* thin_wall;
+        BestPoint search_result;
+        size_t idx_path;
+        ExtrusionLoop *current_loop = nullptr;
+        virtual void use(ExtrusionPath &path) override {
+            //don't consider other thin walls.
+            if (path.role() == erThinWall) return;
+            //for each segment
+            Lines lines = path.polyline.lines();
+            for (size_t idx_line = 0; idx_line < lines.size(); idx_line++) {
+                //look for nearest point
+                double dist = lines[idx_line].distance_to_squared(thin_wall->points.front());
+                if (dist < search_result.dist) {
+                    search_result.path = &path;
+                    search_result.idx_path = idx_path;
+                    search_result.idx_line = idx_line;
+                    search_result.line = lines[idx_line];
+                    search_result.dist = dist;
+                    search_result.from_start = true;
+                    search_result.loop = current_loop;
+                }
+                dist = lines[idx_line].distance_to_squared(thin_wall->points.back());
+                if (dist < search_result.dist) {
+                    search_result.path = &path;
+                    search_result.idx_path = idx_path;
+                    search_result.idx_line = idx_line;
+                    search_result.line = lines[idx_line];
+                    search_result.dist = dist;
+                    search_result.from_start = false;
+                    search_result.loop = current_loop;
+                }
+            }
+        }
+        virtual void use(ExtrusionPath3D &path3D) override { /*shouldn't happen*/ }
+        virtual void use(ExtrusionMultiPath &multipath) override { /*shouldn't happen*/ }
+        virtual void use(ExtrusionMultiPath3D &multipath) { /*shouldn't happen*/ }
+        virtual void use(ExtrusionLoop &loop) override {
+            ExtrusionLoop * last_loop = current_loop;
+            current_loop = &loop;
+            //for each extrusion path
+            idx_path = 0;
+            for (ExtrusionPath &path : loop.paths) {
+                this->use(path);
+                idx_path++;
+            }
+            current_loop = last_loop;
+        }
+        virtual void use(ExtrusionEntityCollection &collection) override {
+            collection.no_sort = false;
+            //for each loop? (or other collections)
+            for (ExtrusionEntity *entity : collection.entities)
+                entity->visit(*this);
+        }
+    };
+    //max dist to branch: ~half external periemeter width
+    coord_t max_width = this->ext_perimeter_flow.scaled_width();
+    SearchBestPoint searcher;
+    ThickPolylines not_added;
+    //search the best extusion/point to branch into
+     //for each thin wall
+    int idx = 0;
+    for (ThickPolyline &tw : thin_walls) {
+        searcher.thin_wall = &tw;
+        searcher.search_result.dist = max_width;
+        searcher.search_result.dist *= searcher.search_result.dist;
+        searcher.search_result.path = nullptr;
+        searcher.use(extrusions);
+        idx++;
+        //now insert thin wall if it has a point
+        //it found a segment
+        if (searcher.search_result.path != nullptr) {
+            if (!searcher.search_result.from_start)
+                tw.reverse();
+            //get the point
+            Point point = tw.points.front().projection_onto(searcher.search_result.line);
+            //we have to create 3 paths: 1: thinwall extusion, 2: thinwall return, 3: end of the path
+            //create new path : end of the path
+            Polyline poly_after;
+            poly_after.points.push_back(point);
+            poly_after.points.insert(poly_after.points.end(),
+                searcher.search_result.path->polyline.points.begin() + searcher.search_result.idx_line + 1,
+                searcher.search_result.path->polyline.points.end());
+            searcher.search_result.path->polyline.points.erase(
+                searcher.search_result.path->polyline.points.begin() + searcher.search_result.idx_line + 1,
+                searcher.search_result.path->polyline.points.end());
+            searcher.search_result.loop->paths[searcher.search_result.idx_path].polyline.points.push_back(point);
+            searcher.search_result.loop->paths.insert(searcher.search_result.loop->paths.begin() + 1 + searcher.search_result.idx_path, 
+                ExtrusionPath(poly_after, *searcher.search_result.path));
+            //create thin wall path exttrusion
+            ExtrusionEntityCollection tws = thin_variable_width({ tw }, erThinWall, this->ext_perimeter_flow);
+            ChangeFlow change_flow;
+            if (tws.entities.size() == 1 && tws.entities[0]->is_loop()) {
+                //loop, just add it 
+                change_flow.percent_extrusion = 1;
+                change_flow.use(tws);
+                //add move back
+
+                searcher.search_result.loop->paths.insert(searcher.search_result.loop->paths.begin() + 1 + searcher.search_result.idx_path,
+                    change_flow.paths.begin(), change_flow.paths.end());
+                //add move to
+
+            } else {
+                //first add the return path
+                ExtrusionEntityCollection tws_second = tws;
+                tws_second.reverse();
+                change_flow.percent_extrusion = 0.1;
+                change_flow.use(tws_second);
+                for (ExtrusionPath &path : change_flow.paths)
+                    path.reverse();
+                //std::reverse(change_flow.paths.begin(), change_flow.paths.end());
+                searcher.search_result.loop->paths.insert(searcher.search_result.loop->paths.begin() + 1 + searcher.search_result.idx_path,
+                    change_flow.paths.begin(), change_flow.paths.end());
+                //add the real extrusion path
+                change_flow.percent_extrusion = 0.9;
+                change_flow.paths = std::vector<ExtrusionPath>();
+                change_flow.use(tws);
+                searcher.search_result.loop->paths.insert(searcher.search_result.loop->paths.begin() + 1 + searcher.search_result.idx_path,
+                    change_flow.paths.begin(), change_flow.paths.end());
+            }
+        } else {
+            not_added.push_back(tw);
+        }
+    }
+
+    //now add thinwalls that have no anchor (make them reversable)
+    ExtrusionEntityCollection tws = thin_variable_width(not_added, erThinWall, this->ext_perimeter_flow);
+    extrusions.append(tws.entities);
+}
+
 PerimeterIntersectionPoint
 PerimeterGenerator::_get_nearest_point(const PerimeterGeneratorLoops &children, ExtrusionLoop &myPolylines, const coord_t dist_cut, const coord_t max_dist) const {
     //find best points of intersections

src/libslic3r/PerimeterGenerator.hpp

@@ -98,9 +98,15 @@ private:
     double      _mm3_per_mm_overhang;
     Polygons    _lower_slices_p;
 
+    // transform loops into ExtrusionEntityCollection, adding also thin walls into it.
     ExtrusionEntityCollection _traverse_loops(const PerimeterGeneratorLoops &loops, ThickPolylines &thin_walls) const;
+    // try to merge thin walls to a current periemter exrusion or just add it to the end of the list.
+    void _merge_thin_walls(ExtrusionEntityCollection &extrusions, ThickPolylines &thin_walls) const;
+    // like _traverse_loops but with merging all periemter into one continuous loop
     ExtrusionLoop _traverse_and_join_loops(const PerimeterGeneratorLoop &loop, const PerimeterGeneratorLoops &childs, const Point entryPoint) const;
+    // sub-function of _traverse_and_join_loops, transform a single loop as a cut extrusion to be merged with an other one.
     ExtrusionLoop _extrude_and_cut_loop(const PerimeterGeneratorLoop &loop, const Point entryPoint, const Line &direction = Line(Point(0,0),Point(0,0))) const;
+    // sub-function of _traverse_and_join_loops, find the good splot to cut a loop to be able to join it with an other one
     PerimeterIntersectionPoint _get_nearest_point(const PerimeterGeneratorLoops &children, ExtrusionLoop &myPolylines, const coord_t dist_cut, const coord_t max_dist) const;
 };
 

src/libslic3r/PrintConfig.cpp

@@ -3174,6 +3174,15 @@ void PrintConfigDef::init_fff_params()
     def->min = 0;
     def->set_default_value(new ConfigOptionFloatOrPercent(50, true));
 
+    def = this->add("thin_walls_merge", coBool);
+    def->label = L("merging with perimeters");
+    def->full_label = L("Thin wall merge");
+    def->category = OptionCategory::perimeter;
+    def->tooltip = L("Allow the external periemter to merge the thin wals int he path. !!! IF you disable this setting, please explain me why (via help->report issue)"
+        " because I'm going to DELETE this setting next release, as i don't see why someone may want to disable it.");
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionBool(true));
+
     def = this->add("thin_walls_speed", coFloat);
     def->label = L("Thin walls");
     def->full_label = L("Thin walls speed");

src/libslic3r/PrintConfig.hpp

@@ -541,6 +541,7 @@ public:
     ConfigOptionInt                 support_material_threshold;
     ConfigOptionBool                support_material_with_sheath;
     ConfigOptionFloatOrPercent      support_material_xy_spacing;
+    ConfigOptionBool                thin_walls_merge;
     ConfigOptionFloat               xy_size_compensation;
     ConfigOptionFloat               xy_inner_size_compensation;
     ConfigOptionBool                wipe_into_objects;
@@ -599,6 +600,7 @@ protected:
         OPT_PTR(support_material_xy_spacing);
         OPT_PTR(support_material_threshold);
         OPT_PTR(support_material_with_sheath);
+        OPT_PTR(thin_walls_merge);
         OPT_PTR(xy_size_compensation);
         OPT_PTR(xy_inner_size_compensation);
         OPT_PTR(wipe_into_objects);

src/slic3r/GUI/Preset.cpp

@@ -542,6 +542,7 @@ const std::vector<std::string>& Preset::print_options()
         "milling_post_process",
         "milling_extra_size",
         "milling_speed",
+        "thin_walls_merge",
     };
     return s_opts;
 }