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
