The sweep compares a curve with another segment over a y-span shorter than
its tolerance by bounding boxes only, so an edge rising by less than that
tolerance (e.g. a rectangle edge cut through a circle's cap, whose computed
intersection end sits ~1e-12 off the horizontal) was mis-ordered and the
result lost a corner: xor/difference/area disagreed by up to 10%. Every
sweep input now snaps on-curve y values within the tolerance to one level
(handles follow and are levelled with their anchor), so such edges become
exact horizontals, which the sweep handles exactly.
- tests/regressions.rs: the six minimal failures found by the properties,
the root cause in isolation, and the self-crossing "star" polygon.
- The star-polygon strategy rejected no angular step of half a turn or
more, so it sometimes drew self-crossing polygons (the shoelace failure).
- Property suites run from a fixed seed (PROPTEST_CASES / PROPTEST_RNG_SEED
still override), so CI cannot fail at random.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
bflatastic
Brandon Thomas