feat(#182): port handle_all_collisions as a pure Core unit (Slice 2a)
PhysicsObjUpdate.HandleAllCollisions — retail CPhysicsObj::handle_all_collisions (0x00514780, pc:282647): the velocity 'bleed on block' decision. fsf<=1 → reflect the into-surface component (v += -(v·n)(elasticity+1)·n) unless staying-on-walkable (retail's should_reflect guard, restoring the broader rule AD-25 suppressed); INELASTIC zeros instead; fsf>1 → v=0 entirely (the airborne-stuck fix). Bit round-trip owned by the Core resolve writeback (Slice 1), not re-encoded here. 7 conformance tests green. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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78
src/AcDream.Core/Physics/PhysicsObjUpdate.cs
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src/AcDream.Core/Physics/PhysicsObjUpdate.cs
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using System.Numerics;
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namespace AcDream.Core.Physics;
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/// <summary>
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/// Verbatim port of the collision-response tail of retail
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/// <c>CPhysicsObj::UpdateObjectInternal</c>: the velocity decision that
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/// <c>SetPositionInternal</c> (0x00515330) drives through
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/// <c>handle_all_collisions</c> (0x00514780, pc:282647). Kept as a pure function over a
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/// <see cref="PhysicsBody"/> + the resolve outcome so the whole decision is unit-testable
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/// in Core, independent of the App per-frame loop. The transition INTERNALS
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/// (<c>ResolveWithTransition</c> and below) are untouched.
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/// </summary>
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public static class PhysicsObjUpdate
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{
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/// <summary>
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/// retail <c>handle_all_collisions</c> (0x00514780). Reflects or zeros the body's
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/// <see cref="PhysicsBody.Velocity"/> (retail m_velocityVector) based on
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/// <see cref="PhysicsBody.FramesStationaryFall"/>:
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/// <list type="bullet">
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/// <item>fsf ≤ 1 → reflect the into-surface component
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/// (<c>v += -(v·n)(elasticity+1)·n</c>, pc:282712) when we should reflect and a
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/// collision normal is valid; an INELASTIC mover zeros instead (pc:282720).</item>
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/// <item>fsf > 1 → <c>v = 0</c> entirely (pc:282729) — the "bleed on block" that
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/// lets gravity resume so a blocked jump falls/glides off (fixes the #182
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/// airborne-stuck wedge).</item>
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/// </list>
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/// The Stationary* transient-bit round-trip (pc:282737-758) is owned by the Core resolve
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/// writeback (<c>PhysicsEngine.ResolveWithTransition</c>), not re-encoded here.
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/// </summary>
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/// <param name="body">The mover.</param>
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/// <param name="collisionNormalValid">Was a wall/creature collision normal recorded this resolve.</param>
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/// <param name="collisionNormal">Outward collision normal (points away from the surface).</param>
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/// <param name="prevContact">Whether the body had Contact BEFORE this resolve committed
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/// (retail arg3 — reserved for environment-collision reporting; unused today).</param>
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/// <param name="prevOnWalkable">Whether the body was OnWalkable before this resolve (retail arg4).</param>
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/// <param name="nowOnWalkable">Whether the body is OnWalkable after this resolve.</param>
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public static void HandleAllCollisions(
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PhysicsBody body,
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bool collisionNormalValid, Vector3 collisionNormal,
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bool prevContact, bool prevOnWalkable, bool nowOnWalkable)
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{
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// var_10_1 (pc:282653-282657): reflect UNLESS the mover stays on walkable ground
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// (and is not sledding). This restores retail's broader rule — the AD-25 airborne-only
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// suppression is retired: the landing-snap fragility it guarded is gone (landing state
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// is now owned by the SetPositionInternal-derived contact flags, not a Velocity.Z<=0
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// gate). A grounded corridor wall-slide keeps its tangential velocity (should_reflect
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// false), exactly as retail.
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bool sledding = body.State.HasFlag(PhysicsStateFlags.Sledding);
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bool shouldReflect = !(prevOnWalkable && nowOnWalkable && !sledding);
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if (body.FramesStationaryFall <= 1)
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{
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if (shouldReflect && collisionNormalValid)
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{
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if (body.State.HasFlag(PhysicsStateFlags.Inelastic))
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{
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body.Velocity = Vector3.Zero; // pc:282720-282722
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}
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else
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{
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float dot = Vector3.Dot(body.Velocity, collisionNormal);
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if (dot < 0f) // moving INTO the surface
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{
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float k = -(dot * (body.Elasticity + 1f)); // pc:282712
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body.Velocity += collisionNormal * k;
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}
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}
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}
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}
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else
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{
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body.Velocity = Vector3.Zero; // fsf>1 → THE BLEED (pc:282729)
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}
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_ = prevContact; // retail report_environment_collision(arg3) — weenie collision events, later.
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}
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}
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tests/AcDream.Core.Tests/Physics/HandleAllCollisionsTests.cs
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tests/AcDream.Core.Tests/Physics/HandleAllCollisionsTests.cs
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using System.Numerics;
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using AcDream.Core.Physics;
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using Xunit;
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namespace AcDream.Core.Tests.Physics;
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/// <summary>
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/// Conformance tests for <see cref="PhysicsObjUpdate.HandleAllCollisions"/> — the port of
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/// retail <c>CPhysicsObj::handle_all_collisions</c> (0x00514780, pc:282647). This is the
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/// velocity "bleed on block" decision: reflect (fsf≤1) vs zero (fsf>1).
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/// </summary>
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public class HandleAllCollisionsTests
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{
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private static PhysicsBody Airborne(Vector3 v, int fsf = 0) => new PhysicsBody
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{
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State = PhysicsStateFlags.Gravity | PhysicsStateFlags.ReportCollisions,
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TransientState = TransientStateFlags.None,
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Velocity = v,
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FramesStationaryFall = fsf,
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};
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[Fact]
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public void Fsf0_AirborneWallHit_ReflectsIntoWallComponent()
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{
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var b = Airborne(new Vector3(3f, 0f, 0f)); // moving +X into a wall whose outward normal is -X
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var n = new Vector3(-1f, 0f, 0f);
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PhysicsObjUpdate.HandleAllCollisions(b,
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collisionNormalValid: true, collisionNormal: n,
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prevContact: false, prevOnWalkable: false, nowOnWalkable: false);
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// dot = 3*-1 = -3 < 0 → k = -(-3*(0.05+1)) = 3.15 → v += (-1,0,0)*3.15 → x = 3 - 3.15 = -0.15
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Assert.Equal(-0.15f, b.Velocity.X, precision: 3);
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}
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[Fact]
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public void Fsf0_MovingAwayFromSurface_DoesNotReflect()
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{
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var b = Airborne(new Vector3(0f, 0f, 2f)); // moving up, normal also up (already separating)
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var n = new Vector3(0f, 0f, 1f);
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PhysicsObjUpdate.HandleAllCollisions(b,
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collisionNormalValid: true, collisionNormal: n,
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prevContact: false, prevOnWalkable: false, nowOnWalkable: false);
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Assert.Equal(2f, b.Velocity.Z); // dot = +2 >= 0 → no reflection
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}
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[Fact]
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public void Fsf2_ZeroesVelocity_TheAirborneStuckBleed()
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{
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// The #182 case: a straight-up jump blocked by a near-horizontal creature normal.
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// At fsf>1 the whole velocity is zeroed so gravity resumes → the player falls/glides off.
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var b = Airborne(new Vector3(0f, 0f, 18f), fsf: 2);
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var n = new Vector3(-0.96f, -0.25f, -0.15f);
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PhysicsObjUpdate.HandleAllCollisions(b,
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collisionNormalValid: true, collisionNormal: n,
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prevContact: false, prevOnWalkable: false, nowOnWalkable: false);
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Assert.Equal(Vector3.Zero, b.Velocity);
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}
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[Fact]
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public void Fsf3_ZeroesVelocity_EvenWithoutCollisionNormal()
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{
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var b = Airborne(new Vector3(1f, 2f, 18f), fsf: 3);
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PhysicsObjUpdate.HandleAllCollisions(b,
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collisionNormalValid: false, collisionNormal: default,
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prevContact: false, prevOnWalkable: false, nowOnWalkable: false);
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Assert.Equal(Vector3.Zero, b.Velocity);
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}
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[Fact]
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public void StayingOnWalkable_DoesNotReflect_CorridorWallSlidePreserved()
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{
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// Grounded before AND after → should_reflect is false → the tangential wall-slide
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// velocity is preserved (retail's rule; the corridor shuffle, not a sticky bounce).
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var b = new PhysicsBody
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{
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Velocity = new Vector3(3f, 0f, 0f),
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TransientState = TransientStateFlags.Contact | TransientStateFlags.OnWalkable,
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FramesStationaryFall = 0,
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};
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var n = new Vector3(-1f, 0f, 0f);
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PhysicsObjUpdate.HandleAllCollisions(b,
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collisionNormalValid: true, collisionNormal: n,
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prevContact: true, prevOnWalkable: true, nowOnWalkable: true);
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Assert.Equal(3f, b.Velocity.X);
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}
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[Fact]
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public void Inelastic_ZeroesInsteadOfReflecting()
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{
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var b = Airborne(new Vector3(3f, 0f, 0f));
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b.State |= PhysicsStateFlags.Inelastic; // spell projectile / missile
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var n = new Vector3(-1f, 0f, 0f);
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PhysicsObjUpdate.HandleAllCollisions(b,
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collisionNormalValid: true, collisionNormal: n,
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prevContact: false, prevOnWalkable: false, nowOnWalkable: false);
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Assert.Equal(Vector3.Zero, b.Velocity);
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}
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[Fact]
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public void LandingReflects_RetailRuleRestored_NotSuppressed()
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{
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// prev airborne → now grounded (a landing). Retail reflects here too (AD-25 retired);
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// at elasticity 0.05 the effect is a tiny, imperceptible deflection.
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var b = Airborne(new Vector3(0f, 0f, -5f)); // falling
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var n = new Vector3(0f, 0f, 1f); // floor normal up
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PhysicsObjUpdate.HandleAllCollisions(b,
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collisionNormalValid: true, collisionNormal: n,
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prevContact: false, prevOnWalkable: false, nowOnWalkable: true);
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// dot = -5 < 0 → k = -(-5*1.05) = 5.25 → v.z = -5 + 5.25 = 0.25 (tiny bounce)
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Assert.Equal(0.25f, b.Velocity.Z, precision: 3);
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}
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}
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