Clipper.Engine - fixed bug in ClipperBase.CheckSplitOwner. (#1029)

Author: AngusJohnson

CPP/Clipper2Lib/src/clipper.engine.cpp

@@ -1,6 +1,6 @@
 /*******************************************************************************
 * Author    :  Angus Johnson                                                   *
-* Date      :  11 October 2025                                                 *
+* Date      :  5 November 2025                                                 *
 * Website   :  https://www.angusj.com                                          *
 * Copyright :  Angus Johnson 2010-2025                                         *
 * Purpose   :  This is the main polygon clipping module                        *
@@ -2940,8 +2940,10 @@ namespace Clipper2Lib {
 
   bool ClipperBase::CheckSplitOwner(OutRec* outrec, OutRecList* splits)
   {
-    for (auto split : *splits)
+    // nb: use indexing (not an iterator) in case 'splits' is modified inside this loop (#1029)
+    for (size_t idx = 0; idx < splits->size(); ++idx)
     {
+      OutRec* split = (*splits)[idx]; 
       if (!split->pts && split->splits &&
         CheckSplitOwner(outrec, split->splits)) return true; //#942
       split = GetRealOutRec(split);

CSharp/Clipper2Lib/Clipper.Engine.cs

@@ -1,6 +1,6 @@
 /*******************************************************************************
 * Author    :  Angus Johnson                                                   *
-* Date      :  11 October 2025                                                 *
+* Date      :  5 November 2025                                                 *
 * Website   :  https://www.angusj.com                                          *
 * Copyright :  Angus Johnson 2010-2025                                         *
 * Purpose   :  This is the main polygon clipping module                        *
@@ -3080,9 +3080,10 @@ private bool CheckBounds(OutRec outrec)
 
     private bool CheckSplitOwner(OutRec outrec, List<int>? splits)
     {
-      foreach (int i in splits!)
+      // nb: use indexing (not an iterator) in case 'splits' is modified inside this loop (#1029)
+      for (int i = 0; i < splits!.Count; i++)
       {
-        OutRec? split = _outrecList[i];
+        OutRec? split = _outrecList[splits[i]];
         if (split.pts == null && split.splits != null &&
           CheckSplitOwner(outrec, split.splits)) return true; //#942
         split = GetRealOutRec(split);

Delphi/Clipper2Lib/Clipper.Engine.pas

@@ -2,7 +2,7 @@
 
 (*******************************************************************************
 * Author    :  Angus Johnson                                                   *
-* Date      :  11 October 2025                                                 *
+* Date      :  5 November 2025                                                 *
 * Website   :  https://www.angusj.com                                          *
 * Copyright :  Angus Johnson 2010-2025                                         *
 * Purpose   :  This is the main polygon clipping module                        *
@@ -3747,9 +3747,12 @@ function TClipperBase.CheckSplitOwner(outrec: POutRec; const splits: TOutRecArra
   // returns true if a valid owner is found in splits
   // (and also assigns it to outrec.owner)
   Result := true;
-  for i := 0 to High(splits) do
+  // nb: use indexing (not an iterator) in case 'splits' is modified inside
+  // this loop, and also accommodate the length of splits changing (#1029)
+  i := 0;
+  while (i < Length(splits)) do
   begin
-    split := splits[i];
+    split := splits[i]; inc(i);
     if not Assigned(split.pts) and Assigned(split.splits) and
       CheckSplitOwner(outrec, split.splits) then Exit; // Result := true (#942)