Fixed the orientation of ExtrusionLoops when Arachne is used.

src/libslic3r/Arachne/WallToolPaths.cpp

@@ -18,6 +18,8 @@
 
 #include <boost/log/trivial.hpp>
 
+//#define ARACHNE_STITCH_PATCH_DEBUG
+
 namespace Slic3r::Arachne
 {
 
@@ -549,7 +551,7 @@ void WallToolPaths::stitchToolPaths(std::vector<VariableWidthLines> &toolpaths,
         VariableWidthLines stitched_polylines;
         VariableWidthLines closed_polygons;
         PolylineStitcher<VariableWidthLines, ExtrusionLine, ExtrusionJunction>::stitch(wall_lines, stitched_polylines, closed_polygons, stitch_distance);
-#ifdef DEBUG
+#ifdef ARACHNE_STITCH_PATCH_DEBUG
         for (const ExtrusionLine& line : stitched_polylines) {
             if ( ! line.is_odd && line.polylineLength() > 3 * stitch_distance && line.size() > 3) {
                 BOOST_LOG_TRIVIAL(error) << "Some even contour lines could not be closed into polygons!";
@@ -608,7 +610,7 @@ void WallToolPaths::stitchToolPaths(std::vector<VariableWidthLines> &toolpaths,
                 }
             }
         }
-#endif // DEBUG
+#endif // ARACHNE_STITCH_PATCH_DEBUG
         wall_lines = stitched_polylines; // replace input toolpaths with stitched polylines
 
         for (ExtrusionLine& wall_polygon : closed_polygons)

src/libslic3r/Arachne/utils/ExtrusionLine.cpp

@@ -232,6 +232,35 @@ int64_t ExtrusionLine::calculateExtrusionAreaDeviationError(ExtrusionJunction A,
     }
 }
 
+bool ExtrusionLine::is_contour() const
+{
+    if (!this->is_closed)
+        return false;
+
+    Polygon poly;
+    poly.points.reserve(this->junctions.size());
+    for (const ExtrusionJunction &junction : this->junctions)
+        poly.points.emplace_back(junction.p);
+
+    // Arachne produces contour with clockwise orientation and holes with counterclockwise orientation.
+    return poly.is_clockwise();
+}
+
+double ExtrusionLine::area() const
+{
+    assert(this->is_closed);
+    double a = 0.;
+    if (this->junctions.size() >= 3) {
+        Vec2d p1 = this->junctions.back().p.cast<double>();
+        for (const ExtrusionJunction &junction : this->junctions) {
+            Vec2d p2 = junction.p.cast<double>();
+            a += cross2(p1, p2);
+            p1 = p2;
+        }
+    }
+    return 0.5 * a;
+}
+
 } // namespace Slic3r::Arachne
 
 namespace Slic3r {

src/libslic3r/Arachne/utils/ExtrusionLine.hpp

@@ -189,6 +189,10 @@ struct ExtrusionLine
      * \param weighted_average_width The weighted average of the widths of the two colinear extrusion segments
      * */
     static int64_t calculateExtrusionAreaDeviationError(ExtrusionJunction A, ExtrusionJunction B, ExtrusionJunction C, coord_t& weighted_average_width);
+
+    bool is_contour() const;
+
+    double area() const;
 };
 
 static inline Slic3r::ThickPolyline to_thick_polyline(const Arachne::ExtrusionLine &line_junctions)

src/libslic3r/PerimeterGenerator.cpp

@@ -354,6 +354,8 @@ static ClipperLib_Z::Paths clip_extrusion(const ClipperLib_Z::Path &subject, con
 struct PerimeterGeneratorArachneExtrusion
 {
     Arachne::ExtrusionLine *extrusion = nullptr;
+    // Indicates if closed ExtrusionLine is a contour or a hole. Used it only when ExtrusionLine is a closed loop.
+    bool is_contour = false;
     // Should this extrusion be fuzzyfied on path generation?
     bool fuzzify = false;
 };
@@ -414,11 +416,18 @@ static ExtrusionEntityCollection traverse_extrusions(const PerimeterGenerator &p
 
         // Append paths to collection.
         if (!paths.empty()) {
-            if (extrusion->is_closed)
-                extrusion_coll.entities.emplace_back(new ExtrusionLoop(std::move(paths)));
-            else
+            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();
+
+                extrusion_coll.append(std::move(extrusion_loop));
+            } else
                 for (ExtrusionPath &path : paths)
-                    extrusion_coll.entities.emplace_back(new ExtrusionPath(std::move(path)));
+                    extrusion_coll.append(ExtrusionPath(std::move(path)));
         }
     }
 
@@ -541,7 +550,7 @@ void PerimeterGenerator::process_arachne()
             }
 
             auto &best_path = all_extrusions[best_candidate];
-            ordered_extrusions.push_back({best_path, false});
+            ordered_extrusions.push_back({best_path, best_path->is_contour(), false});
             processed[best_candidate] = true;
             for (size_t unlocked_idx : blocking[best_candidate])
                 blocked[unlocked_idx]--;