From ca45619b2b4cc595fd9441ec518f64587646fcd6 Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@klayout.de>
Date: Fri, 21 Aug 2026 01:17:25 +0200
Subject: [PATCH] WIP

---
 src/db/db/dbPLCTriangulation.cc              | 34 +++++------
 src/db/unit_tests/dbPLCTriangulationTests.cc | 60 ++++++++++++++++++++
 2 files changed, 77 insertions(+), 17 deletions(-)

diff --git a/src/db/db/dbPLCTriangulation.cc b/src/db/db/dbPLCTriangulation.cc
index face8c8f0..a00cf49b9 100644
--- a/src/db/db/dbPLCTriangulation.cc
+++ b/src/db/db/dbPLCTriangulation.cc
@@ -241,36 +241,36 @@ Triangulation::insert (Vertex *vertex, std::list<tl::weak_ptr<Polygon> > *new_tr
   }
 
   //  check, if the new vertex is on an edge (may be edge between triangles or edge on outside)
-  std::vector<Edge *> on_edges;
+  Edge *on_edge = 0;
   std::vector<Edge *> on_vertex;
   for (int i = 0; i < 3; ++i) {
+
     Edge *e = tris.front ()->edge (i);
-#if 0 // @@@
-    if (e->side_of (*vertex) == 0) {
-#else // @@@
+
     auto ee = e->edge ();
-    double snap = 1e-3;
-    if (std::abs (ee.distance (*vertex)) < snap * ee.length ()) {
-#endif // @@@
-      if (is_equal (*vertex, *e->v1 ()) || is_equal (*vertex, *e->v2 ())) {
+    double snap_range = 1e-5 * ee.length ();
+
+    // @@@ refine? generalize "snap_range"? change "is_equal" in general?
+    if (std::abs (ee.distance (*vertex)) < snap_range) {
+      if (vertex->distance (*e->v1 ()) < snap_range || vertex->distance (*e->v2 ()) < snap_range) {
         on_vertex.push_back (e);
-      } else {
-        on_edges.push_back (e);
+      } else if (! on_edge) {
+        on_edge = e;
       }
     }
+
   }
 
-  if (! on_vertex.empty ()) {
+  if (on_edge) {
+
+    split_triangles_on_edge (vertex, on_edge, new_triangles);
+    return vertex;
+
+  } else if (! on_vertex.empty ()) {
 
     tl_assert (on_vertex.size () == size_t (2));
     return on_vertex.front ()->common_vertex (on_vertex [1]);
 
-  } else if (! on_edges.empty ()) {
-
-    tl_assert (on_edges.size () == size_t (1));
-    split_triangles_on_edge (vertex, on_edges.front (), new_triangles);
-    return vertex;
-
   } else if (tris.size () == size_t (1)) {
 
     //  the new vertex is inside one triangle
diff --git a/src/db/unit_tests/dbPLCTriangulationTests.cc b/src/db/unit_tests/dbPLCTriangulationTests.cc
index f867ee40b..44b90ff97 100644
--- a/src/db/unit_tests/dbPLCTriangulationTests.cc
+++ b/src/db/unit_tests/dbPLCTriangulationTests.cc
@@ -1078,6 +1078,65 @@ TEST(triangulate_issue1996)
   EXPECT_LT (plc.num_polygons (), size_t (132000));
 }
 
+TEST(triangulate_discussion_2883)
+{
+  db::DPoint contour[] = {
+    db::DPoint (-13025.428, -33338.541),
+    db::DPoint (-13127.959, -33236.01),
+    db::DPoint (-13132.732, -33240.783),
+    db::DPoint (-13135.914, -33237.601),
+    db::DPoint (-13026.136, -33127.823),
+    db::DPoint (-12923.605, -33230.354),
+    db::DPoint (-12920.423, -33227.172),
+    db::DPoint (-13022.954, -33124.641),
+    db::DPoint (-13014.999, -33116.686),
+    db::DPoint (-13011.817, -33119.868),
+    db::DPoint (-13016.59, -33124.641),
+    db::DPoint (-12914.059, -33227.172),
+    db::DPoint (-12923.605, -33236.718),
+    db::DPoint (-13026.136, -33134.187),
+    db::DPoint (-13029.317, -33137.369),
+    db::DPoint (-12926.787, -33239.899),
+    db::DPoint (-12936.333, -33249.445),
+    db::DPoint (-13038.863, -33146.915),
+    db::DPoint (-13042.045, -33150.097),
+    db::DPoint (-12939.515, -33252.627),
+    db::DPoint (-12949.061, -33262.173),
+    db::DPoint (-13051.591, -33159.643),
+    db::DPoint (-13054.773, -33162.825),
+    db::DPoint (-12952.243, -33265.355),
+    db::DPoint (-13012.701, -33325.813),
+    db::DPoint (-13115.231, -33223.283),
+    db::DPoint (-13118.413, -33226.464),
+    db::DPoint (-13015.882, -33328.995)
+  };
+
+  db::DPolygon poly;
+  poly.assign_hull (contour + 0, contour + sizeof (contour) / sizeof (contour[0]));
+
+  double dbu = 0.001;
+
+  db::plc::TriangulationParameters param;
+  param.min_b = 0.3;
+
+  db::plc::Graph plc;
+  TestableTriangulation tri (&plc);
+  db::DCplxTrans trans = db::DCplxTrans (dbu) * db::DCplxTrans (db::DTrans (db::DPoint () - poly.box ().center ()));
+  tri.triangulate (trans * poly, param);
+
+  EXPECT_EQ (tri.check (false), true);
+
+  //  for debugging:
+  //  tri.dump ("debug.gds");
+
+  for (auto t = plc.begin (); t != plc.end (); ++t) {
+    EXPECT_GE (t->b (), param.min_b);
+  }
+
+  EXPECT_GE (plc.num_polygons (), size_t (70));
+  EXPECT_LE (plc.num_polygons (), size_t (72));
+}
+
 TEST(triangulate_with_vertexes)
 {
   db::Point contour[] = {
@@ -1172,3 +1231,4 @@ TEST(triangulate_with_vertexes)
     }
   }
 }
+