FA-88393 / Mesh topology invariants / Member archive

An empty face list is reported as a closed oriented surface · case 03

Empty meshes pass watertightness checks.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Input: polygon faces. Empty input returns "empty". Consecutive repeated indices form no edge (skip that pair only). Undirected edges used once are boundary, twice interior, more non-manifold; an interior edge whose two uses have the same direction is inconsistent. Verdict precedence: non-manifold, then "non-orientable-or-inconsistent", then "open-oriented" (boundary present), else "closed-oriented". Return [boundary, interior, nonmanifold, inconsistent, verdict].

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
empty	`[0, 0, 0, 0, "closed-oriented"]`	`"empty"`	Failed

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