From 93d9298b5101cb88fcdf15c84f0a3dd49ecb0d45 Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@klayout.de>
Date: Wed, 15 Feb 2023 00:29:26 +0100
Subject: [PATCH] Formally minkowsky sum now is allowed with empty polygon
 arguments

---
 src/db/db/dbPolygonTools.cc | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/db/db/dbPolygonTools.cc b/src/db/db/dbPolygonTools.cc
index 2032eeb36..0202ee908 100644
--- a/src/db/db/dbPolygonTools.cc
+++ b/src/db/db/dbPolygonTools.cc
@@ -2143,6 +2143,10 @@ ms_extraction (db::EdgeProcessor &ep, bool resolve_holes)
 static db::Polygon 
 do_minkowski_sum (const db::Polygon &a, const db::Edge &b, bool resolve_holes)
 {
+  if (a.begin_hull () == a.end_hull ()) {
+    return db::Polygon ();
+  }
+
   db::EdgeProcessor ep;
   db::ms_production (a, b.p1 (), b.p2 (), ep);
   return db::ms_extraction (ep, resolve_holes);
@@ -2161,7 +2165,9 @@ minkowski_sum (const db::Polygon &a, const db::Edge &b, bool rh)
 static db::Polygon 
 do_minkowski_sum (const db::Polygon &a, const db::Polygon &b, bool resolve_holes)
 {
-  tl_assert (a.begin_hull () != a.end_hull ());
+  if (a.begin_hull () == a.end_hull () || b.begin_hull () == b.end_hull ()) {
+    return db::Polygon ();
+  }
 
   db::Vector p0 = *a.begin_hull () - db::Point ();