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fix(physics): port retail Layer-2 ethereal override -- open doors passable (pc:276961)

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CPhysicsObj::FindObjCollisions at pc:276961-276989 has a two-layer mechanism for
ethereal doors. Layer 1 (BSPQuery Path-1 sphere_intersects_solid, pc:323742) already
ported in Task 3 handles the open-gap case. Layer 2 (pc:276963-276977) is a
force-reset that catches the residual case: when the player's sphere CENTER crosses
a thin ethereal slab, sphere_intersects_solid can still return Collided via
HitsSphere (polygon contact on the slab face). Without Layer 2, the opened door
remains an invisible wall until the player's center passes ~0.48m beyond the slab.

Port: in FindObjCollisionsInCell, immediately after the shape dispatch (BSP / Sphere /
Cylinder branches), insert the Layer-2 gate:
  if (result != OK && sp.ObstructionEthereal && !sp.StepDown && (obj.State & 0x1u) == 0)
    { result = OK; ci.CollisionNormalValid = false; }
The STATIC_PS (0x1) guard (pc:276969) ensures static-ethereal env geometry still
blocks. Cylinder/Sphere shapes already return OK from their own ObstructionEthereal
early-outs so Layer 2 is effectively BSP-only in practice, but is written
unconditionally matching retail.

Tests (ObstructionEtherealTests): three new BSP Layer-2 cases using a synthetic
wall polygon in local-space coordinates. (A) ethereal non-static: passable. (B)
ethereal+static: still blocks. (C) non-ethereal: still blocks. All 11 tests pass;
DoorCollision/CellarUp/CornerFlood/HouseExitWalk regression gate: 25/25 pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-06-24 21:03:08 +02:00
parent 6c7e3ef1ab
commit 1a7c5aa006
2 changed files with 248 additions and 34 deletions
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31
src/AcDream.Core/Physics/TransitionTypes.cs
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@ -2775,6 +2775,37 @@ public sealed class Transition
}
}
// Layer-2 ethereal override — retail CPhysicsObj::FindObjCollisions
// pc:276961-276989 (0x0050f1ac-0x0050f31e). After the shape dispatch
// (Layer 1), retail force-resets the result to OK for a NON-STATIC
// ethereal target when step_down is NOT set. Layer 1 (BSPQuery Path-1
// sphere_intersects_solid) handles the no-solid-leaf case (open door
// gap) already, but a thin ethereal slab (closed-but-ethereal / the
// player's sphere CENTER crosses the slab) can still return Collided.
// Layer 2 suppresses that so the door is FULLY passable once ethereal.
//
// Gate conditions (pc:276963-276973):
// 276963: state_3 != OK_TS ← result is a block
// 276967: sphere_path.step_down == 0 ← not a step-down query
// 276969: (target->state & 1) == 0 ← NOT STATIC_PS (0x1)
// 276971: var_c != 0 || ... ← obstruction_ethereal set
// (the || ... is the IGNORE_CREATURES+creature case — handled
// upstream in CollisionExemption; Layer 2 only needs the var_c term)
// Effect (pc:276973-276977):
// state_3 = OK_TS ← force passable
// collision_normal_valid = 0 ← clear stale slide normal
// Note: Cylinder and Sphere shapes already return OK from their own
// obstruction_ethereal early-out, so this clause only fires in practice
// for the BSP branch, but is written unconditionally as retail does.
if (result != TransitionState.OK
&& sp.ObstructionEthereal
&& !sp.StepDown
&& (obj.State & 0x1u) == 0) // STATIC_PS=0x1 (acclient.h:2815): static ethereal keeps Layer-1 only
{
result = TransitionState.OK;
ci.CollisionNormalValid = false; // collision_normal_valid = 0 (pc:276975)
}
// L.2a slice 3: attribute the collision (if any) to this entity.
// Two cases:
// - result != OK: the object stopped the transition (hard-block).