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fix(physics): skip mesh-AABB-fallback cylinder for landblock stabs

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ISSUES #83 Phase A1. Landblock stabs (entity.Id 0xC0XXYY00+n per
LandblockLoader.cs:55) were being registered with TWO collision
shadows: the correct per-part BSP at `entity.Id*256 + partIdx`, AND a
redundant mesh-AABB-fallback cylinder at `entity.Id`. The fallback
clamped to 1.5m radius, centered at the building's mesh origin,
producing user-reported "thin air" collisions inside cottages and
within 2m of building exteriors.

The fallback was originally designed for canopy-only-BSP procedural
scenery (0x80XXYY00+n) — trees whose BSP covers the canopy but not
the trunk. Landblock stabs have full BSP coverage and don't need it.

Probe evidence (launch-thinair capture):
- 0xC0A9B479 cylinder fallback (Holtburg cottage): 104 hits in a
  short capture session, all inside the cottage main room
  (cell=0xA9B4013F), ~2m from the building's mesh origin.
- 0xA9B47900 BSP (the actual cottage walls): 52 legitimate hits.

Fix: one new bool _isLandblockStab + one clause in the existing
mesh-AABB-fallback gate.

Spec: docs/superpowers/specs/2026-05-21-cylinder-fallback-dedup-design.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-05-20 11:42:13 +02:00
parent bb1e919ef2
commit 5f2b545979
3 changed files with 363 additions and 0 deletions
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12
src/AcDream.App/Rendering/GameWindow.cs
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@ -5827,6 +5827,17 @@ public sealed class GameWindow : IDisposable
|| ((entity.Id < 0x40000000u) // stab
&& (_srcPrefix == 0x01000000u || _srcPrefix == 0x02000000u));
bool _isScenery = _isOutdoorMesh;
// ISSUES #83 / Phase A1 (2026-05-21): landblock stabs
// (LandBlockInfo.Objects + Buildings) use entity.Id with the
// 0xC0XXYY00+n layout per LandblockLoader.cs:55. Their BSP
// collision covers the whole structure; the mesh-AABB-fallback
// path below is for canopy-only-BSP procedural scenery
// (0x80XXYY00+n) and produces a redundant 1.5m-clamped
// invisible disc at the stab's mesh origin — the user-reported
// "thin air" collision inside cottages. Gate the fallback to
// exclude stabs. Spec:
// docs/superpowers/specs/2026-05-21-cylinder-fallback-dedup-design.md.
bool _isLandblockStab = (entity.Id & 0xFF000000u) == 0xC0000000u;
if (_isScenery) scTried++;
// Register EACH physics-enabled part so multi-part Setups
// (buildings, trees) have all their collision geometry registered.
@ -6048,6 +6059,7 @@ public sealed class GameWindow : IDisposable
// L-fix3: skip entirely when the Setup is phantom — retail
// decorative meshes have no collision data on purpose.
if (!isPhantomSetup
&& !_isLandblockStab
&& (_isOutdoorMesh || (entityBsp == 0 && entityCyl == 0))
&& entity.MeshRefs.Count > 0)
{