FA-87419 / Collision detection broadphase / Member archive

Fat box size test uses half perimeter instead of area · case 04

The shrink rule triggers at the wrong sizes.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

solve(tight, fat, disp, margin, mult): dynamic-tree proxy update. If the stored fat box contains the new tight box (inclusive) and its area is at most 4x that of a freshly built fat box, keep it: [False, fat]. Otherwise rebuild: tight expanded by margin on all sides, then extended by mult*disp on the side the motion points to; return [True, rebuilt box rounded to 6].

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 2	`[false, [-3.0, -4.3, 2.9, -0.4]]`	`[true, [-1.1, -3.4, 1.1, -2.3]]`	Failed

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