Fixing the infill order for concentric infill to outside-in.

Relies to:
Concentric Fill Start Point - New Feature Request #4948
Feature Request: Archimedean Chords - Option to define direction of travel (Inside-Out or Outside-In) #5214

src/libslic3r/ClipperUtils.cpp

@@ -716,45 +716,33 @@ static void traverse_pt_noholes(const ClipperLib::PolyNodes &nodes, Polygons *ou
     });
 }
 
-static void traverse_pt_old(ClipperLib::PolyNodes &nodes, Polygons* retval)
+static void traverse_pt_outside_in(const ClipperLib::PolyNodes &nodes, Polygons *retval)
 {
-    /* use a nearest neighbor search to order these children
-       TODO: supply start_near to chained_path() too? */
-    
     // collect ordering points
     Points ordering_points;
     ordering_points.reserve(nodes.size());
-    for (ClipperLib::PolyNodes::const_iterator it = nodes.begin(); it != nodes.end(); ++it) {
-        Point p((*it)->Contour.front().X, (*it)->Contour.front().Y);
-        ordering_points.push_back(p);
-    }
-    
-    // perform the ordering
-    ClipperLib::PolyNodes ordered_nodes = chain_clipper_polynodes(ordering_points, nodes);
-    
-    // push results recursively
-    for (ClipperLib::PolyNodes::iterator it = ordered_nodes.begin(); it != ordered_nodes.end(); ++it) {
+    for (const ClipperLib::PolyNode *node : nodes)
+        ordering_points.emplace_back(node->Contour.front().X, node->Contour.front().Y);
+
+    // Perform the ordering, push results recursively.
+    //FIXME pass the last point to chain_clipper_polynodes?
+    for (const ClipperLib::PolyNode *node : chain_clipper_polynodes(ordering_points, nodes)) {
+        retval->emplace_back(ClipperPath_to_Slic3rPolygon(node->Contour));
+        if (node->IsHole()) 
+            // Orient a hole, which is clockwise oriented, to CCW.
+            retval->back().reverse();
         // traverse the next depth
-        traverse_pt_old((*it)->Childs, retval);
-        retval->push_back(ClipperPath_to_Slic3rPolygon((*it)->Contour));
-        if ((*it)->IsHole()) retval->back().reverse();  // ccw
+        traverse_pt_outside_in(node->Childs, retval);
     }
 }
 
-Polygons union_pt_chained(const Polygons &subject, bool safety_offset_)
+Polygons union_pt_chained_outside_in(const Polygons &subject, bool safety_offset_)
 {
     ClipperLib::PolyTree polytree = union_pt(subject, safety_offset_);
     
     Polygons retval;
-    traverse_pt_old(polytree.Childs, &retval);
+    traverse_pt_outside_in(polytree.Childs, &retval);
     return retval;
-    
-// TODO: This needs to be tested:
-//    ClipperLib::PolyTree polytree = union_pt(subject, safety_offset_);
-    
-//    Polygons retval;
-//    traverse_pt_noholes(polytree.Childs, &retval);
-//    return retval;
 }
 
 Polygons simplify_polygons(const Polygons &subject, bool preserve_collinear)

src/libslic3r/ClipperUtils.hpp

@@ -219,7 +219,7 @@ ClipperLib::PolyTree union_pt(const Slic3r::ExPolygons &subject, bool safety_off
 ClipperLib::PolyTree union_pt(Slic3r::Polygons &&subject, bool safety_offset_ = false);
 ClipperLib::PolyTree union_pt(Slic3r::ExPolygons &&subject, bool safety_offset_ = false);
 
-Slic3r::Polygons union_pt_chained(const Slic3r::Polygons &subject, bool safety_offset_ = false);
+Slic3r::Polygons union_pt_chained_outside_in(const Slic3r::Polygons &subject, bool safety_offset_ = false);
 
 ClipperLib::PolyNodes order_nodes(const ClipperLib::PolyNodes &nodes);
 

src/libslic3r/Fill/FillConcentric.cpp

@@ -24,22 +24,22 @@ void FillConcentric::_fill_surface_single(
         this->spacing = unscale<double>(distance);
     }
 
-    Polygons loops = (Polygons)expolygon;
+    Polygons loops = to_polygons(std::move(expolygon));
     Polygons last  = loops;
     while (! last.empty()) {
         last = offset2(last, -(distance + min_spacing/2), +min_spacing/2);
-        loops.insert(loops.end(), last.begin(), last.end());
+        append(loops, last);
     }
 
     // generate paths from the outermost to the innermost, to avoid
     // adhesion problems of the first central tiny loops
-    loops = union_pt_chained(loops, false);
+    loops = union_pt_chained_outside_in(loops, false);
     
     // split paths using a nearest neighbor search
     size_t iPathFirst = polylines_out.size();
     Point last_pos(0, 0);
     for (const Polygon &loop : loops) {
-        polylines_out.push_back(loop.split_at_index(last_pos.nearest_point_index(loop.points)));
+        polylines_out.emplace_back(loop.split_at_index(last_pos.nearest_point_index(loop.points)));
         last_pos = polylines_out.back().last_point();
     }
 

src/libslic3r/Fill/FillConcentric.hpp

@@ -8,7 +8,7 @@ namespace Slic3r {
 class FillConcentric : public Fill
 {
 public:
-    ~FillConcentric() override {}
+    ~FillConcentric() override = default;
 
 protected:
     Fill* clone() const override { return new FillConcentric(*this); };

src/libslic3r/Print.cpp

@@ -1851,10 +1851,7 @@ void Print::_make_brim()
         }
         polygons_append(loops, offset(islands, -0.5f * float(flow.scaled_spacing())));
     }
-    loops = union_pt_chained(loops, false);
-    // The function above produces ordering well suited for concentric infill (from outside to inside).
-    // For Brim, the ordering should be reversed (from inside to outside).
-    std::reverse(loops.begin(), loops.end());
+    loops = union_pt_chained_outside_in(loops, false);
 
     // If there is a possibility that brim intersects skirt, go through loops and split those extrusions
     // The result is either the original Polygon or a list of Polylines