From e9de4252fb98f15aee4dc68f28c555036642013a Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@koefferlein.de>
Date: Mon, 17 Sep 2018 01:25:10 +0200
Subject: [PATCH] Fixed #166 (internal error when writing GDS file)

This fix consists of computing the intersection
points in the split procedure with higher resolution
to avoid topology changes due to snapping on the cut
line.
---
 src/db/db/dbPolygonTools.cc         |  8 ++++----
 src/db/unit_tests/dbPolygonTools.cc | 17 +++++++++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/db/db/dbPolygonTools.cc b/src/db/db/dbPolygonTools.cc
index 77f7c9dcd..e44ecfa8b 100644
--- a/src/db/db/dbPolygonTools.cc
+++ b/src/db/db/dbPolygonTools.cc
@@ -112,7 +112,7 @@ struct cut_polygon_edge
 {
   typedef typename PointType::coord_type coord_type;
   typedef typename db::edge<coord_type> edge_type;
-  typedef typename db::coord_traits<coord_type>::area_type projection_type;
+  typedef double projection_type;
 
   cut_polygon_edge ()
     : contour (-1), index (0), projected (0), point (), last_point ()
@@ -179,7 +179,7 @@ public:
 
   bool operator< (const loose_end_struct<CuttingEdgeType> &other) const
   {
-    if (proj () != other.proj ()) {
+    if (! db::coord_traits<double>::equal (proj (), other.proj ())) {
       return proj () < other.proj ();
     } else {
       return db::vprod_sign (edge (), other.edge ()) > 0;
@@ -196,13 +196,13 @@ static bool _cut_polygon_internal (const PolygonType &input, const Edge &line, C
   typedef db::edge<coord_type> edge_type;
   typedef cut_polygon_edge<point_type> cut_polygon_edge_type;
   typedef cut_polygon_segment<cut_polygon_edge_type> cutting_segment_type;
-  typedef typename db::coord_traits<coord_type>::area_type projection_type;
 
   bool do_hole_assignment = (input.holes () > 0);
   std::vector <PolygonType> hull_polygons;
   std::vector <PolygonType> hole_polygons;
 
   std::vector<cutting_segment_type> cutting_segments;
+  double line_length = line.double_length ();
 
   for (unsigned int nc = 0; nc < input.holes () + 1; ++nc) {
 
@@ -229,7 +229,7 @@ static bool _cut_polygon_internal (const PolygonType &input, const Edge &line, C
         int s1 = line.side_of (e.p1 ());
         int s2 = line.side_of (e.p2 ());
 
-        projection_type p = db::sprod (ip.second - line.p1 (), line.p2 () - line.p1 ());
+        double p = line_length * double (db::vprod (e.p1 () - line.p1 (), e.d ())) / double (db::vprod (line.d (), e.d ()));
 
         if (s1 < 0 && s2 >= 0) {
           // right -> left or on edge
diff --git a/src/db/unit_tests/dbPolygonTools.cc b/src/db/unit_tests/dbPolygonTools.cc
index 06224c533..6229f89f4 100644
--- a/src/db/unit_tests/dbPolygonTools.cc
+++ b/src/db/unit_tests/dbPolygonTools.cc
@@ -2241,3 +2241,20 @@ TEST(403)
     EXPECT_EQ (right_of.size (), size_t (0));
   }
 }
+
+//  issue 166
+TEST(404)
+{
+  db::Polygon poly;
+  std::string s ("(390,0;438,936;176,874;0,832;438,937;541,961;821,102)");
+  tl::Extractor ex (s.c_str ());
+  ex.read (poly);
+
+  std::vector<db::Polygon> sp;
+  db::split_polygon (poly, sp);
+  EXPECT_EQ (sp.size (), size_t (2));
+  if (sp.size () >= 2) {
+    EXPECT_EQ (sp[0].to_string (), "(390,0;438,936;390,925;438,937;541,961;821,102)");
+    EXPECT_EQ (sp[1].to_string (), "(0,832;176,874;390,925)");
+  }
+}