FA-87477 / Collision detection broadphase / Member archive

Objects starting exactly on the midline are treated as straddlers · case 02

Boundary-aligned objects pile up in parent nodes and inflate every query.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

solve(objs, cap, max_depth, q): quadtree over [0,16]^2. Insert [id,minx,miny,maxx,maxy] in order. A node splits when it holds more than cap objects and depth<max_depth; children are ordered cy*2+cx. An object goes to a child only if it fits entirely: maxx<mid -> left, minx>=mid -> right (same for y); straddlers stay. On split all node objects are re-inserted. Query returns [sorted ids of objects in nodes whose closed bounds overlap q, total node count, max depth].

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 3	`[[3, 27], 5, 1]`	`[[27], 5, 1]`	Failed

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

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