Collider transform props / debug issue.

[igpdev-428]

Hi! I'm new to the whole ecosystem. Thank you for all the work and incredible tools I've been finding out.

I'm trying to work with colliders: I have a basic player with a rigidbody and a capsule collider inside. Gravity is turned on. The ground also has a collider and I'm testing several colliders that spawn according to the bounding box size of several meshes in the scene.

ISSUE: When I set some of the props for either the RigidBody or CuboidCollider scale property for the rigidbody in some cases the colliders stop working and it falls through the ground, or it doesn't collide at all. The debug shows the colliders at the right spot.

I've tried several changes, taking the collider out, in, automatic colliders from the rigidbody, etc. Outside of the mesh, inside, etc. Sometimes it works sometimes it doesn't. Usually I can only guarantee collission If I just spawn rigidbody and cuboidcollider without props.

It's pretty sporadic but there are several cases where the debug physics shows a collision should stop movement but it still goes through.

This following example has me confused and it's the same issue but a specific case.

export function MeshWithCollider(props: meshPropsPlus) {
  const colliderSize = new Vector3()
  const colliderCenter = new Vector3()
  props.geometry.boundingBox?.getSize(colliderSize)
  props.geometry.boundingBox?.getCenter(colliderCenter)

  const { position, rotation, scale, ...filteredProps } = props
  console.log('AAA', props.scale)
  return (
    <>
      <mesh {...props} />
      <RigidBody position={props.position} scale={-1.15} type={'fixed'} colliders={false}>
        <CuboidCollider
          position={colliderCenter}
          scale={-1.15} /* this works */
           /*  scale={+1.15}  /* this doesn't , and debug wireframe stays same spot */ */
          args={[colliderSize.x / 2, colliderSize.y / 2, colliderSize.z / 2]}
        />
      </RigidBody>
    </>
  )
}

The scale on the CuboidCollider doesn't affect the box helper that comes with the physics debug flag , but it does cancel the collision when it doesn't coincide in sign with the parent (or when it is missing from the CuboidCollider element). I'm pretty much lost at this point. I have a feeling that the debug mode is not updating correctly with the transform of the CuboidCollider but it's a guess.

Versions used:
"dependencies": {
"react": "^18.3.1",
"react-dom": "^18.3.1",
"@react-three/rapier": "^1.5.0",
"@react-three/drei": "^9.121.4",
"@react-three/fiber": "^8.17.14",
"@react-three/handle": "^6.6.2",
"@react-three/postprocessing": "^2.19.1",

"@react-three/uikit": "^0.8.7",
"@react-three/uikit-apfel": "^0.8.7",
"@react-three/xr": "^6.6.2",
"@types/three": "^0.172.0",
"@vitejs/plugin-react-swc": "^3.7.2",
"iwer": "^2.0.0",
"leva": "^0.10.0",

"three": "^0.173.0",
"vite-tsconfig-paths": "^5.1.4"

},

Thank you in advance and also please ask for any context information I might've missed.

[wiledal]

(moved this to the discussions, as it's not a technical problem with the library)

Hello! 👋

I am unsure what happens when you apply negative values in the scale, but I would recommend not doing that.
When dealing with numbers (not calculations), you should avoid adding + as it could have adverse effects. A positive value in js is represented by anything that is not prefixed with a -.

What happens if you simply do scale={1.15}?

[wiledal]

Here's an example of CuboidColliders being used in conjunction with scales:
https://codesandbox.io/p/devbox/react-three-rapier-auto-colliders-forked-5dc3d2

[igpdev-428]

Hi! Thanks for your quick reply.
I've managed to reproduce my issue in your example.

Just delete the ground and add this below the objects

    <RigidBody
       type="fixed"
       position={[-1, -1, 0]}
       /* scale={+1.15} */
       scale={-1.15}
       colliders={false}
     >
       <CuboidCollider position={[0, 0, 0]} scale={-1.15} args={[2, 1, 1]} />
     </RigidBody>

You'll see that when the sign of the cuboid and the rigidbody coincides the collision works, when one of them is scaled with a different sign it stops working and the objects fall through.

I'm now thinking if this has to do with the normals but this is still an unexpected behaviour, since I'm trying to add automatic coliders inside a tree of objects that sometimes have negative scales.

[wiledal]

Unfortunately, there's no "support" for negative scales for colliders, so I cannot speak for how it would work. However, when doing automatic colliders, it calculates the size based on the bounding shape of the mesh, in which case the negative scale of a mesh should not have an effect as the actual scale value won't be used.

If you place it within a container with negative scale however, things will be wrong immediately as the Physics world does not know that your coordinate system is flipped.

[wiledal]

Here's an example how I walked through a glb I exported from Blender to create an interactive game world.

https://codesandbox.io/p/sandbox/trip-fellas-wip-9d4vm9

Instead of applying rigidbodies to thing immediately, I walk through the meshes and place them in the world.
The best thing is to have the RigidBody in control of the location of an object, as you might get inconsistent rotational behaviors for nested transformed objects.

[igpdev-428]

Your solution is probably the best workaround to the current state, although this is the first time I've encountered this issue in a physics engine

I work from a .glb file and convert it to jsx using glbjsx utility. Many objects in the scene are gonna have negative scales since non-destructive modeling usually works from mirrored duplicated objects that introduces said negative scales inside the objects tree. When I go to apply Rigidbody to a mesh (or replace the mesh with the MeshWithCollider object I was developing), it can be wrapped in a negative scale group or mesh tag somewhere up-stream so that is probably the issue.

I'll be applying all transforms and un-parenting all objects on the original .blend file just to be safe and work with a simple hierarchy of objects.
I'll look a little bit more into the source code of the library so in the future I can suggest a change with some knowledge of what is causing negative scales not being supported. Thanks!

[wiledal]

Yeah, I understand the reasoning for having negative scales from a modeling perspective. In order to keep the tree-hierarchy however, React-Three-Rapier needs to apply things in-line directly to the meshes affected. So if you have...

<group scale={[1, -1, 1]}>
  <RigidBody>
    ...
  <RigidBody />
</group>

...the physics world does not know about the flipped scale, only the starting position and properties of the mesh as seen from the "worlds perspective". Because of the flipped container, the mesh within the scaled object will have a visually reversed gravity since transforming Y positively will visually move the mesh in the opposite direction.

There's literally no way around this, unless we break the hiarchy.

It will probably reflect all scales starting props correctly however, so scaled objects get the right size colliders and starting positions.

[igpdev-428]

I get your point, although the issue here is that colliders stop working (they still fall, but through). Also I just tried adding a group tag with negative scale as parent of one of the torus in your first example and it just disappeared (didn't fall "up", nothing)

I still see this as a general weird behaviour. Regarding the gravity issue you mention the physics tag is above all objects and should convey a "world" view (before and above any scales) and forces applied there should track regardless of the scale. What I do see as a possible source of problems when not handling scale correctly is that scale can switch from a right-hand coordinate system to an inverted, and that sometimes can bring issues to operations between convex geometries and their intersection.

EDIT: I finally found a solution using 'hull' automatic colliders and not 'cuboid' (cuboid positions the collider in the wrong position)

export function MeshWithCollider(props: meshPropsPlus) {
  return (
      <RigidBody type={'fixed'} colliders={'hull'}> /* 'cuboid' doesn't work , colliders goes to wrong position */
        <mesh {...props} visible={true} />
      </RigidBody>
  )
}