The witness-probe overlap test missed small corner intersections: its
candidate points (crossing-edge midpoints and vertex-centroid midpoints)
can all land on a part boundary or outside the intersection, so two 10x10
parts at (0,0) and (9,9) with zero spacing were accepted despite sharing
a 1x1 unit of material.
Route the overlap decision through Collision, which clips triangulated
polygons and keeps only positive-area regions, catching corner overlaps,
containment, and coincident poses while legal edge/corner contact stays
legal. Collision's hole subtraction was conservative (partially-clipped
triangles were kept whole), so a part inside another part's cutout could
false-positive depending on triangulation alignment; subtract holes
exactly instead: a piece outside a convex hole triangle is the union of
its clips against each edge's outside half-space.
Polygon-polygon collision detection using convex decomposition (ear-clipping
triangulation) followed by Sutherland-Hodgman clipping on each triangle pair.
Handles overlapping, non-overlapping, edge-touching, containment, and concave
polygons. Includes hole subtraction support for future use.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
aj
