FA-88593 / Mesh topology invariants / Member archive

Welding removes every repeated corner, not only consecutive ones · case 03

Polygons that legitimately revisit a vertex lose corners.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Input [points, faces, eps]. Points weld when floor(c/eps+0.5) agrees on every coordinate; the welded vertex takes the next new id and is represented by its lowest original index. Remap faces, merge consecutive equal corners (also across the wrap), drop faces with fewer than 3 corners, rotate each face so its smallest id comes first (orientation kept) and drop later copies of an identical rotated face. Return [representatives, faces].

Why this case matters

Mesh processing pipelines (remeshing, export, simulation, printing) trust these topological counts and adjacency answers; a wrong invariant silently accepts broken meshes or rejects valid ones.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
non-consecutive repeat kept	`[[0, 1, 2, 3], [[0, 1, 3, 2]]]`	`[[0, 1, 2, 3], [[0, 1, 3, 2, 3]]]`	Failed

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