Fix assertion failure in Bézier curve intersection handling #9222
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_intersect() skipped parameter-range checks for self-intersection points, incorrectly assuming that any point valid on the supporting Bézier curve was also valid for every derived x-monotone subcurve. For looping curves, that assumption fails: a self-intersection point may lie outside the parameter range of the specific subcurve being processed. These invalid points were being passed to downstream solvers, triggering assertion failures (e.g., roots.size() == 1). This commit forces parameter range verification via _is_in_range() for all intersection points, including those produced by self-intersections.
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…On Sun, 4 Jan 2026 at 19:01, Andreas Fabri ***@***.***> wrote:
@afabri <https://github.com/afabri> requested your review on: #9222
<#9222> Fix assertion failure in Bézier
curve intersection handling.
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Summary of Changes
_intersect() skipped parameter-range checks for self-intersection points, incorrectly assuming that any point valid on the supporting Bézier curve was also valid for every derived x-monotone subcurve.
For looping curves, that assumption fails: a self-intersection point may lie outside the parameter range of the specific subcurve being processed. These invalid points were being passed to downstream solvers, triggering assertion failures (e.g., roots.size() == 1).
This commit forces parameter range verification via _is_in_range() for all intersection points, including those produced by self-intersections.
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