SimplifyPolygons() shrinks triangle
Polygon and line clipping and offsetting library (C++, C#, Delphi)
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#206 SimplifyPolygons() shrinks triangle
Hi,
if you simplify the following (disjunct) triangles, the Y coordinate of path[0] is changed from 20164 tp 20165 in the output, see attached images.
Path path1({ {42901,20164}, {45175,41481}, {42901,44382} });
Path path2({ {11771,20165}, {10056,19990}, {12390,17962} });
Paths simplifiedPaths;
SimplifyPolygons({ path1, path2 }, simplifiedPaths, ClipperLib::pftPositive);
cout << simplifiedPaths << endl;
Output:
(45175,41481), (42901,44382), (42901,20165)
(11771,20165), (10056,19990), (12390,17962)
The bug is located in the scanbeam processing. If the scanbeam intersects two directly connected edges, an the the resulting intersection points have an X distance <0.5, an additional vertex is inserted which should not happen.
--- a/clipper.cpp
+++ b/clipper.cpp
@@ -3054,7 +3054,8 @@ void Clipper::ProcessEdgesAtTopOfScanbeam(const cInt topY)
{
TEdge* ePrev = e->PrevInAEL;
if ((e->OutIdx >= 0) && (e->WindDelta != 0) && ePrev && (ePrev->OutIdx >= 0) &&
- (ePrev->Curr.X == e->Curr.X) && (ePrev->WindDelta != 0))
+ (ePrev->Curr.X == e->Curr.X) && (ePrev->WindDelta != 0) &&
+ (ePrev->Top != e->Top) && (ePrev->Bot != e->Bot))
{
IntPoint pt = e->Curr;
#ifdef use_xyz
I'm not sure if this condition ("edges may not be connected directly") fixes this problem completely.
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