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fix(physics): #90 — sphere-overlap cell stickiness at doorway threshold

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ResolveCellId's indoor-seed fall-through was point-only: when the indoor
BSP push-back moved the foot-sphere CENTER a few cm outside the indoor
CellBSP volume, the resolver flipped CellId back to outdoor. Next tick
re-promoted via CheckBuildingTransit. The ping-pong caused most ticks
to be classified outdoor, bypassing indoor BSP wall checks entirely
and producing the user-reported "walls walk through everywhere in the
inn" symptom.

Fix: port retail's BSPTREE::sphere_intersects_cell_bsp
(acclient_2013_pseudo_c.txt:323267 → BSPNODE variant at :325546) as
BSPQuery.SphereIntersectsCellBsp(node, center, radius). Replace the
point-only check at PhysicsEngine.ResolveCellId:285 with the radius-
aware overlap test. Player stays classified indoor as long as ANY
part of the foot-sphere still overlaps the indoor cell volume; only
flips to outdoor when the sphere is FULLY outside.

Retail uses a 0.01 m epsilon on the radius (acclient :325551); ported
verbatim. 8 new unit tests cover null/leaf/inside/on-plane/straddling/
fully-outside/tangent-boundary cases plus a regression-anchor test
that proves the old PointInsideCellBsp would have returned false for
the same straddling input.

1147 + 8 baseline maintained (was 1139 + 8 before #90 fix). Closes #90.
A4 multi-cell iteration (shipped earlier today) should now actually
exercise in production since the player can stably remain in indoor
cells.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-05-20 20:30:36 +02:00
parent 1534990102
commit 4ca35966f8
3 changed files with 172 additions and 3 deletions
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20
src/AcDream.Core/Physics/PhysicsEngine.cs
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@ -281,12 +281,26 @@ public sealed class PhysicsEngine
if (indoorCell?.CellBSP?.Root is null)
return indoorResult; // Can't verify (no CellBSP); trust FindCellList.
// Issue #90 fix (2026-05-20): use SPHERE-overlap instead of POINT-in
// for the indoor verification. The previous point-only check caused
// a per-frame ping-pong at the inn doorway: indoor BSP push-back
// moved the sphere CENTER a few cm outside the indoor CellBSP
// volume → point-only check returned false → fell through to outdoor
// → next tick re-promoted to indoor → wall hit → push-back →
// outdoor → repeat. Net visual behavior: "walls walk through"
// because outdoor ticks bypass indoor BSP entirely. With sphere-
// overlap, the player stays classified indoor as long as ANY part
// of the foot sphere still overlaps the indoor cell volume.
//
// Retail oracle: CCellStruct::sphere_intersects_cell at
// acclient_2013_pseudo_c.txt:317666 →
// BSPTREE::sphere_intersects_cell_bsp at :323267.
var localCenter = Vector3.Transform(worldPos, indoorCell.InverseWorldTransform);
if (BSPQuery.PointInsideCellBsp(indoorCell.CellBSP.Root, localCenter))
if (BSPQuery.SphereIntersectsCellBsp(indoorCell.CellBSP.Root, localCenter, sphereRadius))
return indoorResult;
// Fall through to outdoor resolution: player has left the indoor
// portal-connected graph entirely.
// Fall through to outdoor resolution: player has FULLY left the
// indoor portal-connected graph (sphere no longer overlaps).
}
// Outdoor seed: use terrain grid to compute the prefixed cell id.