FA-87439 / Collision detection broadphase / Member archive

SAH weights each child area by the other child count · case 04

Unbalanced splits are costed backwards.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

solve(prims): top-down BVH build step. Split axis = larger centroid extent (x on ties). Primitives sorted by centroid on that axis (index tiebreak). Cost of split k = 1 + (P(L)*k + P(R)*(n-k))/P(parent) with P the box perimeter of the primitives' bounds; leaf cost n. Return [best k or 0 for leaf, axis, cost rounded to 6, sorted left indices].

Why this case matters

Broadphase stages decide which object pairs ever reach narrowphase; a wrong boundary, ordering or bookkeeping rule silently drops real contacts or floods the solver with false candidates.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
case 0	`[1, 1, 2.772727, [3]]`	`[5, 1, 6.363636, [0, 1, 2, 3, 4]]`	Failed

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