Fixed regression causing random failures in bridge direction detection. #2636

xs/src/libslic3r/BridgeDetector.cpp

@@ -37,14 +37,10 @@ BridgeDetector::BridgeDetector(const ExPolygon &_expolygon, const ExPolygonColle
     Polygons grown;
     offset((Polygons)this->expolygon, &grown, this->extrusion_width);
     
-    // detect what edges lie on lower slices
-    for (ExPolygons::const_iterator lower = this->lower_slices.expolygons.begin();
-        lower != this->lower_slices.expolygons.end();
-        ++lower) {
-        /*  turn bridge contour and holes into polylines and then clip them
-            with each lower slice's contour */
-        intersection(grown, lower->contour, &this->_edges);
-    }
+    // detect what edges lie on lower slices by turning bridge contour and holes
+    // into polylines and then clipping them with each lower slice's contour
+    intersection(grown, this->lower_slices.contours(), &this->_edges);
+    
     #ifdef SLIC3R_DEBUG
     printf("  bridge has %zu support(s)\n", this->_edges.size());
     #endif

xs/src/libslic3r/ExPolygonCollection.cpp

@@ -112,6 +112,16 @@ ExPolygonCollection::lines() const
     return lines;
 }
 
+Polygons
+ExPolygonCollection::contours() const
+{
+    Polygons contours;
+    for (ExPolygons::const_iterator it = this->expolygons.begin(); it != this->expolygons.end(); ++it) {
+        contours.push_back(it->contour);
+    }
+    return contours;
+}
+
 #ifdef SLIC3RXS
 REGISTER_CLASS(ExPolygonCollection, "ExPolygon::Collection");
 #endif

xs/src/libslic3r/ExPolygonCollection.hpp

@@ -30,6 +30,7 @@ class ExPolygonCollection
     void simplify(double tolerance);
     Polygon convex_hull() const;
     Lines lines() const;
+    Polygons contours() const;
 };
 
 }