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fix(physics): L.4 — steep airborne hits slide-tangent (interim, deviates from retail)

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Phase L.4 closes the "stuck in falling animation on a steep roof" bug
the user reported on 2026-04-30 ("I jump up, I land on it. It should not
even let me land, should just slide with a falling animation"). After
this commit the body no longer sticks to a steep roof when jumping
into it — it slides along the slope while keeping the falling animation.

Two pieces:

1. BSPQuery Path 6 steep-poly slide
   When an airborne sphere hits a polygon whose world normal Z is below
   FloorZ (≈ 0.6642, slope > ~49°), the previous flow was:
   Path 6 SetCollide → Path 4 set_walkable → ContactPlane committed →
   body "lands" on the steep poly with Contact bit + falling animation.
   This left the player stuck mid-slope because OnWalkable was cleared
   but Contact stayed set.

   The new branch detects the steep normal in Path 6 BEFORE SetCollide
   is called. Instead of entering the landing path, it removes the
   into-wall component of the move (project onto the steep face), sets
   CollisionNormal + SlidingNormal, and returns Slid. Same shape as
   Path 5's step-up fallback and CylinderCollision. The resolver retries;
   the sphere is now outside the poly; FindCollisions returns OK;
   ValidateTransition commits the slid position. ContactPlane is never
   set, so the body stays airborne with falling animation.

2. PlayerMovementController L.3a-bounce carve-out + Inelastic stop
   Re-enables the velocity-reflection bounce when the contact normal is
   upward-facing but steeper than walkable (0 < N.Z < FloorZ). The base
   L.3a rule suppresses bounce on landing transitions to avoid micro-
   bounce on flat terrain; that suppression also stuck the player to
   too-steep roofs they shouldn't land on. This carve-out re-enables
   the reflection specifically for the steep upward case.

Also lands related L.2c precipice / edge-slide work that was in flight:

- TransitionTypes EdgeSlideAfterStepDownFailed: walkable-poly-steep
  cliff route + steep-ContactPlane cliff route ordering, so that
  CliffSlide fires when the stored walkable polygon itself is too
  steep (Path 4 had previously accepted it as a "landing" via the
  permissive LandingZ threshold).
- CliffSlide reference-normal selection: prefer LastWalkable, fall back
  to LastKnownContactPlane only when walkable, else use world-up. This
  prevents the cross(steepN, steepN) = 0 degenerate case that left the
  cliff slide as a no-op when both current and last-known were steep.
- Phase 2 / step-down branch / edge-slide branch / cliff-slide
  diagnostic helpers gated on ACDREAM_DUMP_EDGE_SLIDE / ACDREAM_DUMP_STEEP_ROOF.
- Two new airborne-mover regression tests in BSPStepUpTests +
  PhysicsEngineTests covering wall-slide and edge tangent motion.

DEVIATION FROM RETAIL — DOCUMENTED FOR FOLLOW-UP

The Path 6 steep slide is NOT what retail does. Retail's flow on the
same hit is:

  Path 6 SetCollide (no steep check) → Path 4 find_walkable returns
  nothing for steep → Phase 3 reset path: restore_check_pos +
  kill_velocity → return COLLIDED → validate_transition reverts CheckPos
  to CurPos and forces OK.

Net retail behavior: position reverts to pre-failed-move (typically
just below the roof in the common jump-up case), velocity zeroed,
gravity rebuilds Z next frame, body falls back down naturally with
the falling animation. The "freeze" framing I used earlier was wrong;
in the typical case retail just bounces the body off and lets gravity
take over.

Strict retail behavior would match the user's intent better in the
common case AND avoid the bounce-energy-accumulation we saw with the
slide-tangent approach (V grew to ~50 m/s in continuous-contact frames).
However, retail's behavior degenerates in the edge case of an overhead
landing onto a steep slope (body would freeze mid-air above the roof).

This commit ships the slide-tangent fix as an interim "much better"
state per user verification on 2026-04-30. Follow-up work to match
retail strictly: revert Path 6 steep-slide, audit Phase 3 reset to
ensure kill_velocity (matching OBJECTINFO::kill_velocity ->
CPhysicsObj::set_velocity({0,0,0}, 0)) actually fires, and re-test.

Refs:
  - acclient_2013_pseudo_c.txt:323784-323821 (Path 6 SetCollide)
  - acclient_2013_pseudo_c.txt:273191-273239 (Phase 3 reset path)
  - acclient_2013_pseudo_c.txt:272563-272596 (validate_transition revert)
  - acclient_2013_pseudo_c.txt:274467-274475 (kill_velocity)
  - acclient_2013_pseudo_c.txt:282699-282715 (handle_all_collisions bounce)

Tests: 833/833 green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-04-30 13:22:07 +02:00
parent 5210bd3d55
commit b1af56eb19
8 changed files with 417 additions and 16 deletions
Download patch file Download diff file Expand all files Collapse all files

61
src/AcDream.App/Input/PlayerMovementController.cs
View file

@ -441,6 +441,19 @@ public sealed class PlayerMovementController
moverFlags: AcDream.Core.Physics.ObjectInfoState.IsPlayer
| AcDream.Core.Physics.ObjectInfoState.EdgeSlide);
// L.4-diag (2026-04-30): trace position transitions so we can see
// whether the body is actually moving frame-to-frame on the steep
// roof, or whether it's frozen at the impact point.
if (Environment.GetEnvironmentVariable("ACDREAM_DUMP_STEEP_ROOF") == "1"
&& resolveResult.CollisionNormalValid)
{
Console.WriteLine(
$"[steep-roof] FRAME pre=({preIntegratePos.X:F2},{preIntegratePos.Y:F2},{preIntegratePos.Z:F2}) " +
$"post=({postIntegratePos.X:F2},{postIntegratePos.Y:F2},{postIntegratePos.Z:F2}) " +
$"resolved=({resolveResult.Position.X:F2},{resolveResult.Position.Y:F2},{resolveResult.Position.Z:F2}) " +
$"isOnGround={resolveResult.IsOnGround}");
}
// Apply resolved position.
_body.Position = resolveResult.Position;
@ -507,6 +520,47 @@ public sealed class PlayerMovementController
? !(prevOnWalkable && nowOnWalkable)
: (!prevOnWalkable && !nowOnWalkable);
// L.4-steep-landing-bounce (2026-04-30): also bounce on
// landing IF the contact surface is upward-facing but
// steeper than walkable (FloorZ ≈ 49°). Per retail and the
// user's expectation: jumping onto a steep roof should NOT
// result in a landing — the player should bounce off, keep
// the falling animation, and slide off.
//
// Without this: the L.3a base rule suppresses the bounce on
// landing transitions (prev air → now ground) to avoid
// micro-bounce on flat terrain, but that suppression also
// sticks the player to too-steep roofs they shouldn't land
// on. This carve-out re-enables the bounce specifically for
// steep upward-facing surfaces.
//
// Range `0 < N.Z < FloorZ` means "facing upward but too
// steep" — excludes walls (N.Z ≈ 0) which are handled by the
// existing prevAirborne+nowAirborne rule, and ceilings
// (N.Z < 0) which the body shouldn't bounce off the same way.
if (!applyBounce
&& resolveResult.CollisionNormalValid
&& resolveResult.CollisionNormal.Z > 0f
&& resolveResult.CollisionNormal.Z < PhysicsGlobals.FloorZ)
{
applyBounce = true;
}
// L.4-diag (2026-04-30): per-frame bounce trace for steep-roof bug.
bool diagSteep = Environment.GetEnvironmentVariable("ACDREAM_DUMP_STEEP_ROOF") == "1";
if (diagSteep && resolveResult.CollisionNormalValid)
{
var n0 = resolveResult.CollisionNormal;
var v0 = _body.Velocity;
Console.WriteLine(
$"[steep-roof] BOUNCE-CHECK applyBounce={applyBounce} " +
$"prevWalk={prevOnWalkable} nowWalk={nowOnWalkable} " +
$"N=({n0.X:F2},{n0.Y:F2},{n0.Z:F2}) FloorZ={PhysicsGlobals.FloorZ:F2} " +
$"V=({v0.X:F2},{v0.Y:F2},{v0.Z:F2}) " +
$"dot={Vector3.Dot(v0, n0):F3} " +
$"isOnGround={resolveResult.IsOnGround}");
}
if (applyBounce)
{
if (_body.State.HasFlag(PhysicsStateFlags.Inelastic))
@ -526,6 +580,13 @@ public sealed class PlayerMovementController
// velocity reflects (subtle bounce).
float k = -(dotVN * (_body.Elasticity + 1f));
_body.Velocity = v + n * k;
if (diagSteep)
{
var v1 = _body.Velocity;
Console.WriteLine(
$"[steep-roof] BOUNCE-APPLIED V_after=({v1.X:F2},{v1.Y:F2},{v1.Z:F2}) k={k:F3}");
}
}
}
}