feat(physics): L.3a — wall-bounce velocity reflection on airborne hits
Three independent research agents converged: retail's "bouncy walls" feel comes from CPhysicsObj::handle_all_collisions (acclient_2013_pseudo_c.txt: 282699-282715, ACE PhysicsObj.cs:2692-2697) which applies the canonical reflection v_new = v - (1 + e) * dot(v, n) * n to the body's velocity after every transition resolves. Player elasticity = 0.05 (5% bounce); INELASTIC_PS = 0x20000 zeros velocity entirely (used by spell projectiles). acdream had the data plumbed (PhysicsBody.Elasticity = 0.05 was already set, ci.CollisionNormal was being populated in 8+ code paths) but ResolveWithTransition discarded the normal before returning. Hence "sticky walls on jumps" — perpendicular velocity got removed by SlideSphere's geometric resolution, but never reflected back, so hitting a wall mid-jump zeroed forward motion entirely instead of producing a small push-back. Files: - PhysicsBody.cs: add PhysicsStateFlags.Inelastic = 0x20000. - ResolveResult.cs: surface CollisionNormalValid + CollisionNormal. - PhysicsEngine.cs:599-624: copy ci.CollisionNormal into ResolveResult before returning (both ok and partial paths). - PlayerMovementController.cs:445-503: after position commit, apply reflection per the retail formula. Inelastic → zero velocity; else → reflect with v += n * -(dot(v,n) * (e + 1)). apply_bounce rule (more conservative than retail by design): - Sledding: retail's strict rule — bounce unless both grounded. - Otherwise: bounce ONLY when both prev and now airborne. Suppress on landing (prev air, now ground) to avoid micro-bouncing on floor — the post-reflection upward Z defeats the controller's Velocity.Z<=0 landing-snap gate. Retail's elasticity 0.05 makes the artifact visually imperceptible there; acdream's per-frame architecture amplifies it. Tests: 1491 → 1491 still pass (existing AirborneFrames + WalkOffLedge tests confirmed the conservative apply_bounce rule keeps landings clean). Live verification needed: jump into a wall mid-air — should produce a visible bounce-back rather than sticking. Walking along corridor with side-clip should still slide. Landing should still settle without micro-bounce. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Erik
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261322b48e
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4 changed files with 191 additions and 3 deletions
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@ -31,6 +31,14 @@ public enum PhysicsStateFlags : uint
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ReportCollisions = 0x00000010,
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Gravity = 0x00000400, // bit 10 — apply downward gravity
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Hidden = 0x00001000,
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/// <summary>
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/// L.3a (2026-04-30): retail INELASTIC_PS bit (acclient.h:2834).
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/// When set, wall-collisions zero the velocity instead of reflecting.
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/// Used by spell projectiles and missiles that should embed/explode on
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/// impact rather than bounce. The player NEVER has this flag set —
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/// player wall-hits use the reflection path with elasticity ~0.05.
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/// </summary>
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Inelastic = 0x00020000, // bit 17 — retail INELASTIC_PS
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Sledding = 0x00800000, // bit 23 — sledding (modified friction)
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}
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@ -44,6 +52,7 @@ public enum TransientStateFlags : uint
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None = 0,
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Contact = 0x00000001, // bit 0 — touching any surface
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OnWalkable = 0x00000002, // bit 1 — standing on a walkable surface
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Sliding = 0x00000004, // bit 2 — carry sliding normal into next transition
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Active = 0x00000080, // bit 7 — object needs per-frame update
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}
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@ -87,6 +96,9 @@ public sealed class PhysicsBody
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/// <summary>Ground contact-plane normal (+0x130/134/138).</summary>
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public Vector3 GroundNormal { get; set; } = Vector3.UnitZ;
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/// <summary>Last wall/object sliding normal (retail transient Sliding state).</summary>
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public Vector3 SlidingNormal { get; set; }
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// ── persisted contact-plane state (retail PhysicsObj fields) ───────────
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//
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// Retail's PhysicsObj carries its last contact plane FORWARD across frames.
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@ -113,6 +125,18 @@ public sealed class PhysicsBody
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/// <summary>Whether the contact plane is a water surface (affects step behavior).</summary>
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public bool ContactPlaneIsWater { get; set; }
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/// <summary>Whether the previous walkable polygon is available for edge slide.</summary>
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public bool WalkablePolygonValid { get; set; }
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/// <summary>Most recent walkable polygon plane (world-space).</summary>
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public System.Numerics.Plane WalkablePlane { get; set; }
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/// <summary>Most recent walkable polygon vertices (world-space).</summary>
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public Vector3[]? WalkableVertices { get; set; }
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/// <summary>Up vector used by the most recent walkable polygon probe.</summary>
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public Vector3 WalkableUp { get; set; } = Vector3.UnitZ;
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/// <summary>Elasticity coefficient (+0xB0).</summary>
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public float Elasticity { get; set; } = 0.05f;
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@ -518,8 +518,29 @@ public sealed class PhysicsEngine
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body.ContactPlaneIsWater);
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}
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// Retail CPhysicsObj::get_object_info also seeds SlidingNormal when
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// transient_state has bit 2 set. This matters for one-step/frame hits:
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// a wall collision at the end of one transition must project the next
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// frame's movement along the wall instead of hard-stopping again.
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if (body is not null
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&& body.TransientState.HasFlag(TransientStateFlags.Sliding)
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&& body.SlidingNormal.LengthSquared() > PhysicsGlobals.EpsilonSq)
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{
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transition.CollisionInfo.SetSlidingNormal(body.SlidingNormal);
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}
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transition.SpherePath.InitPath(currentPos, targetPos, cellId, sphereRadius, sphereHeight);
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if (isOnGround && body is not null
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&& body.WalkablePolygonValid
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&& body.WalkableVertices is { Length: >= 3 })
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{
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transition.SpherePath.SetWalkable(
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body.WalkablePlane,
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body.WalkableVertices,
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body.WalkableUp);
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}
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bool ok = transition.FindTransitionalPosition(this);
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var sp = transition.SpherePath;
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@ -548,8 +569,43 @@ public sealed class PhysicsEngine
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{
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body.ContactPlaneValid = false;
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}
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if (sp.HasLastWalkablePolygon && sp.LastWalkableVertices is not null)
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{
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body.WalkablePolygonValid = true;
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body.WalkablePlane = sp.LastWalkablePlane;
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body.WalkableVertices = (Vector3[])sp.LastWalkableVertices.Clone();
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body.WalkableUp = sp.LastWalkableUp;
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}
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else if (!isOnGround && !ci.ContactPlaneValid && !ci.LastKnownContactPlaneValid)
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{
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body.WalkablePolygonValid = false;
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body.WalkableVertices = null;
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}
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if (ci.SlidingNormalValid
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&& ci.SlidingNormal.LengthSquared() > PhysicsGlobals.EpsilonSq)
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{
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body.SlidingNormal = ci.SlidingNormal;
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body.TransientState |= TransientStateFlags.Sliding;
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}
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else
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{
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body.SlidingNormal = Vector3.Zero;
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body.TransientState &= ~TransientStateFlags.Sliding;
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}
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}
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// L.3a (2026-04-30): surface the wall normal so callers can apply
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// retail's velocity-reflection bounce (CPhysicsObj::handle_all_collisions
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// at acclient_2013_pseudo_c.txt:282699-282715, ACE PhysicsObj.cs:
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// 2692-2697). The reflection itself is applied in
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// PlayerMovementController after the position commit, gated on
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// apply_bounce = !(prevOnWalkable && newOnWalkable) — airborne wall
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// hits bounce, grounded wall slides don't.
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bool collisionNormalValid = ci.CollisionNormalValid;
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Vector3 collisionNormal = ci.CollisionNormal;
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if (ok)
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{
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bool onGround = ci.ContactPlaneValid
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@ -558,7 +614,9 @@ public sealed class PhysicsEngine
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return new ResolveResult(
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sp.CheckPos,
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ResolveOutdoorCellId(sp.CheckPos, sp.CheckCellId),
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onGround);
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onGround,
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collisionNormalValid,
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collisionNormal);
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}
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// Transition failed (e.g., stuck in corner, too many steps).
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@ -574,6 +632,8 @@ public sealed class PhysicsEngine
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return new ResolveResult(
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sp.CheckPos,
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ResolveOutdoorCellId(sp.CheckPos, partialCellId),
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partialOnGround);
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partialOnGround,
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collisionNormalValid,
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collisionNormal);
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}
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}
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@ -6,8 +6,25 @@ namespace AcDream.Core.Physics;
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/// Result of <see cref="PhysicsEngine.Resolve"/>: the validated
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/// position after collision, the cell the entity ended up in,
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/// and whether they're standing on a surface.
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///
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/// <para>
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/// L.3a (2026-04-30): added optional collision-normal fields so the
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/// caller (typically <see cref="AcDream.App.Input.PlayerMovementController"/>)
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/// can apply retail's velocity-reflection bounce
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/// (<c>v_new = v - (1 + elasticity) * dot(v, n) * n</c>) to the
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/// PhysicsBody after the geometric resolve completes. ACE port mirror:
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/// <c>references/ACE/Source/ACE.Server/Physics/PhysicsObj.cs:2692-2697</c>;
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/// retail equivalent: <c>CPhysicsObj::handle_all_collisions</c> at
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/// <c>acclient_2013_pseudo_c.txt:282699-282715</c>.
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/// </para>
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/// </summary>
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public readonly record struct ResolveResult(
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Vector3 Position,
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uint CellId,
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bool IsOnGround);
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bool IsOnGround,
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/// <summary>True when a wall collision occurred during this resolve
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/// and <see cref="CollisionNormal"/> is meaningful.</summary>
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bool CollisionNormalValid = false,
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/// <summary>Outward surface normal of the wall the sphere hit. Used
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/// by the velocity-reflection step. Pointing away from the wall.</summary>
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Vector3 CollisionNormal = default);
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