M4: engine.physics — Box3D, over a narrow, verified P/Invoke shim

native/physics-native/lingua_physics.c wraps Box3D at a specific pinned commit (47d7f7c — Box3D has no 1.0 release yet, and its only tag, v0.1.0, already diverges from this API, confirmed by diffing headers rather than assuming). The wrapper is deliberately narrow: Box3D's own b3WorldDef/ b3BodyDef/b3ShapeDef are large structs with function pointers, and b3BoxHull's own doc comment says it "has data hanging off the end and cannot be directly copied" — none of that crosses the P/Invoke boundary. Every exported Lingua_* function takes and returns only plain int32/float/ bool scalars, and handles are this shim's own array-index handles, not Box3D's id structs. C# binds them with classic DllImport rather than the newer LibraryImport specifically because LibraryImport's generated marshalling needs AllowUnsafeBlocks even for an all-scalar signature like every one of these — DllImport needs none, keeping this plugin inside the kernel's "no unsafe in the v1 hot path" rule with no exception required. engine.physics adds Rigidbody/BoxCollider/SphereCollider components and PhysicsWorld, which diffs Query<Rigidbody>() against its own tracked set every Stage.FixedUpdate (there's no destruction event to hook) to create and destroy native bodies, steps Box3D once per invocation — Engine.Host's accumulator decides how many times that runs per frame, not this plugin — and writes each body's resulting transform back to GameObject.Transform. IPhysicsService exposes ApplyLinearImpulse/Get/SetLinearVelocity for gameplay code. Verified twice: a standalone C smoke test against the native shim alone (a box dropped from y=5 onto a static ground settles at y≈1.0, exactly where the two half-heights sum to), and the full pipeline through Engine. Host — a headless run with a real scene, --dump showing the same box settling at y=0.9999 after physics, scene load, and Stage.FixedUpdate all went through the real kernel. 5 new automated tests in Engine.Physics. Tests cover the same settling behavior for both shapes, a missing-collider warning that fires once and doesn't throw, cleanup after a GameObject is destroyed mid-simulation, and that an applied impulse actually changes velocity — all passed on the first run. Physics-enabled GameObjects must be root-level for now: PhysicsWorld writes Box3D's world-space transform straight into LocalPosition/ LocalRotation, correct only when local and world space are the same thing. A parented rigidbody needs the same parent-WorldMatrix-inverse handling GizmoMath.WorldToLocalPosition already does for the gizmo — real, not-yet-done work, not silently wrong. Full suite: 81 tests. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01N1qPfzq8TDCUMFMV3UwV5N
2026-09-02 17:05:39 +03:00
parent c2bcb9b9fe
commit 792b626396
20 changed files with 898 additions and 0 deletions
@@ -0,0 +1,130 @@
+using System.Numerics;
+using Engine.Kernel.Diagnostics;
+using Engine.Kernel.World;
+using Engine.Physics.Contracts;
+
+namespace Engine.Physics;
+
+/// <summary>
+/// Owns the one native Box3D world this plugin creates, and the GameObject
+/// &lt;-&gt; native body handle mapping. <see cref="Sync"/> creates bodies for
+/// any GameObject that's grown a Rigidbody since last frame and destroys
+/// bodies for any that lost one (component removed, or the GameObject
+/// itself was destroyed) — there's no destruction event to hook, so this
+/// diffs Query&lt;Rigidbody&gt;() against the tracked set every FixedUpdate
+/// instead. <see cref="Step"/> advances the simulation once and writes
+/// every tracked body's new transform back into its GameObject.
+/// </summary>
+internal sealed class PhysicsWorld : IDisposable
+{
+    private readonly int _handle;
+    private readonly ILogger _log;
+    private readonly Dictionary<GameObject, int> _bodies = [];
+    private readonly HashSet<GameObject> _warnedMissingCollider = [];
+
+    public PhysicsWorld(Vector3 gravity, ILogger log)
+    {
+        _log = log;
+        _handle = Native.Lingua_CreateWorld(gravity.X, gravity.Y, gravity.Z);
+    }
+
+    public void Sync(IWorld world)
+    {
+        var live = new HashSet<GameObject>();
+
+        foreach (var go in world.Query<Rigidbody>())
+        {
+            live.Add(go);
+            if (!_bodies.ContainsKey(go))
+                TryCreateBody(go);
+        }
+
+        if (_bodies.Count == live.Count)
+            return;
+
+        foreach (var stale in _bodies.Keys.Where(go => !live.Contains(go)).ToList())
+        {
+            Native.Lingua_DestroyBody(_bodies[stale]);
+            _bodies.Remove(stale);
+            _warnedMissingCollider.Remove(stale);
+        }
+    }
+
+    public void Step(float timeStep, int subStepCount = 4)
+    {
+        Native.Lingua_WorldStep(_handle, timeStep, subStepCount);
+
+        foreach (var (go, handle) in _bodies)
+        {
+            Native.Lingua_GetBodyTransform(handle, out var px, out var py, out var pz, out var qx, out var qy, out var qz, out var qw);
+
+            var t = go.Transform;
+            t.LocalPosition = new Vector3(px, py, pz);
+            t.LocalRotation = new Quaternion(qx, qy, qz, qw);
+            go.Transform = t;
+        }
+    }
+
+    public void ApplyLinearImpulse(GameObject go, Vector3 impulse, bool wake)
+    {
+        if (_bodies.TryGetValue(go, out var handle))
+            Native.Lingua_ApplyLinearImpulse(handle, impulse.X, impulse.Y, impulse.Z, wake);
+    }
+
+    public Vector3 GetLinearVelocity(GameObject go)
+    {
+        if (!_bodies.TryGetValue(go, out var handle))
+            return Vector3.Zero;
+
+        Native.Lingua_GetLinearVelocity(handle, out var vx, out var vy, out var vz);
+        return new Vector3(vx, vy, vz);
+    }
+
+    public void SetLinearVelocity(GameObject go, Vector3 velocity)
+    {
+        if (_bodies.TryGetValue(go, out var handle))
+            Native.Lingua_SetLinearVelocity(handle, velocity.X, velocity.Y, velocity.Z);
+    }
+
+    private void TryCreateBody(GameObject go)
+    {
+        var rb = go.GetComponent<Rigidbody>()!;
+        var pos = go.Transform.LocalPosition;
+        var rot = go.Transform.LocalRotation;
+
+        var box = go.GetComponent<BoxCollider>();
+        var sphere = go.GetComponent<SphereCollider>();
+
+        int handle;
+        if (box is not null)
+        {
+            handle = Native.Lingua_CreateBoxBody(
+                _handle, pos.X, pos.Y, pos.Z, rot.X, rot.Y, rot.Z, rot.W,
+                box.HalfExtents.X, box.HalfExtents.Y, box.HalfExtents.Z,
+                (int)rb.Type, rb.Density, rb.Friction, rb.Restitution);
+        }
+        else if (sphere is not null)
+        {
+            handle = Native.Lingua_CreateSphereBody(
+                _handle, pos.X, pos.Y, pos.Z, rot.X, rot.Y, rot.Z, rot.W,
+                sphere.Radius, (int)rb.Type, rb.Density, rb.Friction, rb.Restitution);
+        }
+        else
+        {
+            if (_warnedMissingCollider.Add(go))
+                _log.Warn($"'{go.Name}' has a Rigidbody but no BoxCollider/SphereCollider — no physics body created.");
+            return;
+        }
+
+        _bodies[go] = handle;
+    }
+
+    public void Dispose()
+    {
+        foreach (var handle in _bodies.Values)
+            Native.Lingua_DestroyBody(handle);
+
+        _bodies.Clear();
+        Native.Lingua_DestroyWorld(_handle);
+    }
+}