FA-88460 / Mesh topology invariants / Member archive

Queries for absent half-edges return the reversed half-edge · case 05

Asking for a non-existent direction silently returns data for its twin.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input [faces, queries]. Build half-edges (f[i], f[i+1 mod n]) with face index, next and prev half-edges. A repeated directed half-edge returns ["duplicate-halfedge", [a,b]]. For each query (a,b) return null if it is not a half-edge, else [face, next, prev, twin] with twin [b,a] when that directed half-edge exists, else null.

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
quad pair	`[[0, [1, 2], [3, 0], null], [0, [3, 0], [1, 2], [3, 2]], [1, [2, 4], [5, 3], [2, 3]], [1, [5, 3], [2, 4], null], [0, [1, 2], [3, 0], [0, 1]]]`	`[[0, [1, 2], [3, 0], null], [0, [3, 0], [1, 2], [3, 2]], [1, [2, 4], [5, 3], [2, 3]], [1, [5, 3], [2, 4], null], null]`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.