From 41c1206d803500ef58227c05ba6465d8fc34f292 Mon Sep 17 00:00:00 2001
From: David Kaufman <davidgilkaufman@gmail.com>
Date: Mon, 8 Jan 2024 00:52:19 -0500
Subject: [PATCH] Important performance optimization: union Thicken() polygons
 individually, not en masse

---
 src/Mod/Path/libarea/AreaClipper.cpp | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/Mod/Path/libarea/AreaClipper.cpp b/src/Mod/Path/libarea/AreaClipper.cpp
index d3e9ff8397..48f3dc93af 100644
--- a/src/Mod/Path/libarea/AreaClipper.cpp
+++ b/src/Mod/Path/libarea/AreaClipper.cpp
@@ -253,11 +253,15 @@ static void OffsetSpansWithObrounds(const CArea& area, TPolyPolygon &pp_new, dou
 {
 	Clipper c;
     c.StrictlySimple(CArea::m_clipper_simple);
-
+	pp_new.clear();
 
 	for(std::list<CCurve>::const_iterator It = area.m_curves.begin(); It != area.m_curves.end(); It++)
 	{
+                c.Clear();
+                c.AddPaths(pp_new, ptSubject, true);
+                pp_new.clear();
 		pts_for_AddVertex.clear();
+
 		const CCurve& curve = *It;
 		const CVertex* prev_vertex = NULL;
 		for(std::list<CVertex>::const_iterator It2 = curve.m_vertices.begin(); It2 != curve.m_vertices.end(); It2++)
@@ -278,10 +282,9 @@ static void OffsetSpansWithObrounds(const CArea& area, TPolyPolygon &pp_new, dou
 			}
 			prev_vertex = &vertex;
 		}
+                c.Execute(ctUnion, pp_new, pftNonZero, pftNonZero);
 	}
 
-	pp_new.clear();
-	c.Execute(ctUnion, pp_new, pftNonZero, pftNonZero);
 
 	// reverse all the resulting polygons
 	TPolyPolygon copy = pp_new;