From 119865389173c155ff4824e2b0a6d1d9e6e80833 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Fri, 16 Dec 2022 01:55:21 +0300
Subject: [PATCH] Tweak polygon ear clipping to behave well with duplicate
 vertices

---
 .../include/psemek/cg/triangulation/ear_clipping.hpp  | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/libs/cg/include/psemek/cg/triangulation/ear_clipping.hpp b/libs/cg/include/psemek/cg/triangulation/ear_clipping.hpp
index 3490e7d8..d9b3a408 100644
--- a/libs/cg/include/psemek/cg/triangulation/ear_clipping.hpp
+++ b/libs/cg/include/psemek/cg/triangulation/ear_clipping.hpp
@@ -47,6 +47,15 @@ namespace psemek::cg
 			result.edges[i + count].twin = i;
 		}
 
+		auto inside = [robust_tag](auto const & t, auto const & p)
+		{
+			return true
+				&& geom::orientation(robust_tag, t[0], t[1], p) == geom::sign_t::positive
+				&& geom::orientation(robust_tag, t[1], t[2], p) == geom::sign_t::positive
+				&& geom::orientation(robust_tag, t[2], t[0], p) == geom::sign_t::positive
+				;
+		};
+
 		auto edge = result.edge(0);
 		for (IndexType i = 0; i + 3 < count; ++i)
 		{
@@ -64,7 +73,7 @@ namespace psemek::cg
 
 				for (auto k = nnext.next(); k != edge; k = k.next())
 				{
-					if (geom::contains(triangle, at(k.origin().index())))
+					if (inside(triangle, at(k.origin().index())))
 					{
 						ear = false;
 						break;