fix(physics): kinematic collider support for movable platforms - #255
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Let a mass-0 collider that is moved/rotated by a script carry resting dynamic bodies instead of letting them fall through. - makeKinematic + an explicit `kinematic` flag threaded through createRigidBody / addBox / addSphere - auto-promote a static body to kinematic the first time a script moves or rotates it (so existing graphs work without re-authoring) - CCD on dynamic bodies (sized from the collider) to stop fast bodies tunnelling through thin colliders - pin a kinematic body's origin to an authoritative kinematicPosition so rotation cannot accumulate positional drift; reading Bullet's extrapolated transform back was causing runaway blow-ups under non-default gravity - harden the solver (split impulse + more iterations) against deep-penetration velocity spikes Adds unit tests for the kinematic flag arithmetic, CCD wiring, and auto-promotion. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
marco-ponds
marked this pull request as ready for review
July 3, 2026 15:37
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Problem
Rotating (or moving) a physics collider with mass 0 made resting objects fall through it. A mass-0 body is a Bullet static body — teleporting its transform each frame reports zero velocity to the solver, so a resting sphere loses support and tunnels through.
Changes
makeKinematic+ an explicitkinematicflag threaded throughcreateRigidBody/addBox/addSphere. A kinematic body stays mass-0 but is driven by its motionState, so Bullet derives its velocity and carries contacting dynamic bodies.kinematicPosition. Reading Bullet's extrapolated world transform back on a rotation-only update let the body's origin drift and run away — the platform slid off and exploded under non-default gravity. This was the root cause of the gravity-dependent blow-up.Tests
Adds unit tests for the kinematic flag arithmetic, CCD wiring, and auto-promotion. Full physics suite green (71 tests).
Verification
Verified in-editor via preview across multiple gravity settings (default 30, 40, 60): the platform rotates in place, carries the resting sphere, and no longer explodes.
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