Triangles: potential performance improvement in degenerate point set (circle) case.

src/db/db/dbTriangle.cc

@@ -102,6 +102,21 @@ Vertex::has_edge (const TriangleEdge *edge) const
   return false;
 }
 
+size_t
+Vertex::num_edges (int max_count) const
+{
+  if (max_count < 0) {
+    //  NOTE: this can be slow for a std::list, so we have max_count to limit this effort
+    return mp_edges.size ();
+  } else {
+    size_t n = 0;
+    for (auto i = mp_edges.begin (); i != mp_edges.end () && --max_count >= 0; ++i) {
+      ++n;
+    }
+    return n;
+  }
+}
+
 std::string
 Vertex::to_string (bool with_id) const
 {
@@ -112,18 +127,6 @@ Vertex::to_string (bool with_id) const
   return res;
 }
 
-void
-Vertex::remove_edge (db::TriangleEdge *edge)
-{
-  for (auto e = mp_edges.begin (); e != mp_edges.end (); ++e) {
-    if (*e == edge) {
-      mp_edges.erase (e);
-      return;
-    }
-  }
-  tl_assert (false);
-}
-
 int
 Vertex::in_circle (const DPoint &point, const DPoint &center, double radius)
 {
@@ -172,17 +175,20 @@ void
 TriangleEdge::link ()
 {
   mp_v1->mp_edges.push_back (this);
+  m_ec_v1 = --mp_v1->mp_edges.end ();
+
   mp_v2->mp_edges.push_back (this);
+  m_ec_v2 = --mp_v2->mp_edges.end ();
 }
 
 void
 TriangleEdge::unlink ()
 {
   if (mp_v1) {
-    mp_v1->remove_edge (this);
+    mp_v1->remove_edge (m_ec_v1);
   }
   if (mp_v2) {
-    mp_v2->remove_edge (this);
+    mp_v2->remove_edge (m_ec_v2);
   }
   mp_v1 = mp_v2 = 0;
 }

src/db/db/dbTriangle.h

@@ -48,8 +48,9 @@ class DB_PUBLIC Vertex
   : public db::DPoint
 {
 public:
-  typedef std::vector<TriangleEdge *> edges_type;
+  typedef std::list<TriangleEdge *> edges_type;
   typedef edges_type::const_iterator edges_iterator;
+  typedef edges_type::iterator edges_iterator_non_const;
 
   Vertex ();
   Vertex (const DPoint &p);
@@ -63,7 +64,7 @@ public:
 
   edges_iterator begin_edges () const { return mp_edges.begin (); }
   edges_iterator end_edges () const { return mp_edges.end (); }
-  size_t num_edges () const { return mp_edges.size (); }
+  size_t num_edges (int max_count = -1) const;
 
   bool has_edge (const TriangleEdge *edge) const;
 
@@ -88,7 +89,11 @@ public:
 
 private:
   friend class TriangleEdge;
-  void remove_edge (db::TriangleEdge *edge);
+
+  void remove_edge (const edges_iterator_non_const &ec)
+  {
+    mp_edges.erase (ec);
+  }
 
   edges_type mp_edges;
   size_t m_level;
@@ -397,6 +402,7 @@ private:
 
   Vertex *mp_v1, *mp_v2;
   Triangle *mp_left, *mp_right;
+  Vertex::edges_iterator_non_const m_ec_v1, m_ec_v2;
   size_t m_level;
   size_t m_id;
   bool m_is_segment;

src/db/db/dbTriangles.cc

@@ -724,7 +724,7 @@ Triangles::remove_inside_vertex (db::Vertex *vertex, std::list<tl::weak_ptr<db::
 
   bool make_new_triangle = true;
 
-  while (vertex->num_edges () > 3) {
+  while (vertex->num_edges (4) > 3) {
 
     db::TriangleEdge *to_flip = 0;
     for (auto e = vertex->begin_edges (); e != vertex->end_edges () && to_flip == 0; ++e) {
@@ -746,9 +746,9 @@ Triangles::remove_inside_vertex (db::Vertex *vertex, std::list<tl::weak_ptr<db::
 
   }
 
-  if (vertex->num_edges () > 3) {
+  if (vertex->num_edges (4) > 3) {
 
-    tl_assert (vertex->num_edges () == 4);
+    tl_assert (vertex->num_edges (5) == 4);
 
     //  This case can happen if two edges attached to the vertex are collinear
     //  in this case choose the "join" strategy