Merge of KHR_collision_shapes extension

[eoineoineoin]

Draft of an extension which describes generic, non-renderable shapes suitable for collision detection.

As discussed, we may want to add a skin property to the convex and trimesh shapes; realistically, this functionality would likely come with a performance penalty, but there are valid use-cases which would want this ability.

[EricGriffith]

1. It would be great to include example usage of the schemas in the spec.

2. both seems to be a typo here:

   As both the mesh shape

3. The convex property name is confusing. To me, it implies that the mesh is required to be convex. I prefer the previous version where convex and mesh were separate shapes. If momentum means it they must stay combined, please use a more descriptive name like convexHull.

4. The skin and weights properties should probably be disallowed when a mesh shape is used together with a node that uses the same mesh for rendering. Otherwise, every extension using these shapes will need to repeat the same normative text explaining the precedence of the two (node + shape) skin properties and the three (node + mesh + shape) weights properties.

[npolys]

note that in X3D

Collision for navigation can be a property on Grouping Node types

https://web3d.org/documents/specifications/19775-1/V4.0/Part01/components/navigation.html#Collision

and then there is a whole Rigid Body Physics Component for other object-object collisions https://web3d.org/documents/specifications/19775-1/V4.0/Part01/components/rigidBodyPhysics.html

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From: Aaron Franke @.> Sent: Thursday, May 30, 2024 6:17 PM To: KhronosGroup/glTF @.> Cc: Subscribed @.***> Subject: Re: [KhronosGroup/glTF] Merge of KHR_collision_shapes extension (PR #2370)

@aaronfranke commented on this pull request.

The contents of this PR do not match the repo in which the extension was developed: https://github.com/eoineoineoin/glTF_Physics/tree/master/extensions/2.0/Khronos/KHR_collision_shapes/schema

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In extensions/2.0/Khronos/KHR_collision_shapes/schema/glTF.KHR_collision_shapes.shape.mesh.schema.jsonhttps://github.com/KhronosGroup/glTF/pull/2370#discussion_r1621478845:

• "skin": {
• "description": "The index of a skin with which to deform the mesh.",
• "allOf": [ { "$ref": "glTFid.schema.json" } ]
• },
• "weights": {
• "type": "array",
• "description": "The weights of the instantiated morph target.",
• "minItems": 1,
• "items": {
• "type": "number"
• }
• },

I'm confused, why are skins and weights used for collision meshes? Where was the discussion on this? What is the use case?

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