FA-88472 / Mesh topology invariants / Member archive

Only one endpoint of a boundary edge is marked boundary · case 02

Half the boundary vertices are treated as interior and judged against valence 6.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Input: polygon faces. Neighbours of a vertex are the other endpoints of its edges (consecutive face corners, skipping coincident pairs). Boundary vertices are endpoints of edges used by exactly one face. Irregular vertices have valence != 6 (interior) or != 4 (boundary). Return [{vertex: valence}, irregular count, sorted boundary vertices].

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
fan	`[{"0": 4, "1": 2, "2": 3, "3": 3, "4": 2}, 4, [0, 1, 2, 3]]`	`[{"0": 4, "1": 2, "2": 3, "3": 3, "4": 2}, 4, [0, 1, 2, 3, 4]]`	Failed

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