Fix Bentley-Ottmann polygon walk at shared vertices#382
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When building result polygons, the next segment at a vertex was only searched in one direction around the snap-square event ring. Offset stroke outlines (e.g. dense adjacent cells) could leave no match and panic. Search both directions, fall back to another left endpoint in the result, and close the contour to the other endpoint instead of panicking when no neighbor exists. Add regression tests for merged grid stroke/settle. Co-authored-by: Cursor <cursoragent@cursor.com>
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Summary
bentleyOttmannwhen building result polygons at vertices where many segments meet (e.g. afterPath.Stroke→Settleon dense, shared-edge geometry such as merged Voronoi cell outlines).path_intersection_voronoi_test.go).Problem
Path.StrokecallsSettle(Positive)on the offset outline. At tight junctions, polygon walking only searched one direction for the next segment at a vertex. When no match was found, the code panicked:next node for result polygon is nil, probably buggy intersection codeTest plan
go test ./...in this repoTestVoronoiCanvasMergedStroke_denseGrid)Made with Cursor