Remove degenerate triangles when generating triangle mesh.

src/groupmesh.cpp

@@ -346,6 +346,11 @@ void Group::GenerateShellAndMesh() {
         SMesh outm = {};
         GenerateForBoolean<SMesh>(&prevm, &thism, &outm, srcg->meshCombine);
 
+        // Remove degenerate triangles; if we don't, they'll get split in SnapToMesh
+        // in every generated group, resulting in polynomial increase in triangle count,
+        // and corresponding slowdown.
+        outm.RemoveDegenerateTriangles();
+
         // And make sure that the output mesh is vertex-to-vertex.
         SKdNode *root = SKdNode::From(&outm);
         root->SnapToMesh(&outm);

src/mesh.cpp

@@ -1114,3 +1114,13 @@ void SMesh::PrecomputeTransparency() {
         return (opaquea != opaqueb && opaquea == true);
     });
 }
+
+void SMesh::RemoveDegenerateTriangles() {
+    for(auto &tr : l) {
+        bool isDegenerate = tr.a.OnLineSegment(tr.b, tr.c) ||
+                            tr.b.OnLineSegment(tr.a, tr.c) ||
+                            tr.c.OnLineSegment(tr.a, tr.b);
+        tr.tag = (int)isDegenerate;
+    }
+    l.RemoveTagged();
+}

src/polygon.h

@@ -278,6 +278,7 @@ public:
     void MakeOutlinesInto(SOutlineList *sol, EdgeKind type);
 
     void PrecomputeTransparency();
+    void RemoveDegenerateTriangles();
 
     bool IsEmpty() const;
     void RemapFaces(Group *g, int remap);