Rotate kinematic body based on current rotation

[AdamRamberg]

First of all, thanks for an excellent package!

Now for my question. Is there a straight forward way to rotate a kinematic body based on its current rotation? The way that I have come up with looks like this, but it feels unnecessary complicated just because I don't have access to the body itself (only the mesh):

function Box(props) {
  const [ref, api] = useBox(() => ({
    mass: 0,
    type: 'Kinematic',
    position: [0, 0, 0],
    ...props,
  }))

  useFrame(() => {
    var multQuat = new THREE.Quaternion().setFromAxisAngle(new THREE.Vector3(0, 1, 0), 0.01)
    var newQuat = ref.current.quaternion.clone().multiply(multQuat)
    var newEuler = new THREE.Euler().setFromQuaternion(newQuat)
    api.rotation.set(newEuler.x, newEuler.y, newEuler.z)
  })

  return (
      <mesh ref={ref} position={[0, 0, 0]}>
        <boxBufferGeometry attach="geometry" />
        <meshStandardMaterial attach="material" color="#ff77aa" />
      </mesh>
  )
}

The reason why this is not working for me:

  useFrame(() => {
    let euler = ref.current.rotation.clone()
    euler.y = euler.y + 0.01
    api.rotation.set(euler.x, euler.y, euler.z)
  })

is that the rotation (euler) is not "wraping" (not sure about the correct term here) on the mesh rotation, meaning that x, y and z can only have a value between -PI / 2 and PI / 2.

If I had direct access to the body I would be able to simplify my example to:

  useFrame(() => {
    let newEuler = new CANNON.Vec3()
    ref.current.body.quaternion.toEuler(newEuler)
    newEuler.y = newEuler.y + 0.01
    api.rotation.set(newEuler.x, newEuler.y, newEuler.z)
  })

Maybe there is a simple solution that I don't see, and if that is the case please enlighten me. However, if this indeed is something that isn't easily done using the current API I would propose there being the possibility to pass in a function to api.rotation.set (and probably to the other setters as well). The function would look like this:
(currentRot) => [x, y, z]
My example above would then be:
api.rotation.set((currentRot) => [currentRot).x, currentRot).y + 0.01, currentRot).z])

[codynova]

Hey @AdamRamberg, it looks like you probably want to subscribe to the current rotation of the physics body, right?

const rotation = useRef([ 0, 0, 0 ])
useEffect(() => api.rotation.subscribe((r) => (rotation.current = r)), [])
useFrame() => {
  //...
  rotation.current[1] += 0.01
  api.rotation.set(...rotation)
})

[codynova]

@AdamRamberg Moved to discussions until we can establish an issue

[AdamRamberg]

Hi @codynova! That is indeed a much cleaner solution than mine. Thanks a bunch! Don't think (at least for now / my usecase) that my solution above is needed then.