Vertex Group Assignment

[mholiv]

Feature Request

It would be nice if we could assign components to vertex groups like we can other nested Blender elements. I imagine we could just get the children in Bevy the same way we could for elements like we do now.

Thanks for all of the work you are doing on all things Bevy.

[ChristopherBiscardi]

I imagine we could just get the children in Bevy the same way we could for elements like we do now.

Skein doesn't currently do any hierarchy-based manipulation. All of the types that Skein supports are individual node entries in the gltf file (scene, node, mesh, material, etc) which means the implementation is a one-to-one mapping: "when X is spawned, insert the components associated with it". Which also consequently means there's places to store the data for each node, etc.

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I'm not against this on a conceptual level, but I (or someone else) need to do more discovery on how vertex groups translate into gltf, then into bevy entities. I currently don't see any other data associated with vertex groups in blender (there's no custom properties for vertex groups, for example), and I don't see them show up in the gltf file as nodes of any kind.

I think from a brief cursory overview that the vertex groups are only entries in the mesh entry primitive arrays, but I'm not sure that helps. Here's an example of the data afaict. Note that we lose the vertex group names entirely.

{
  "meshes": [
    {
      "name": "SomeMesh",
      "primitives": [
        {
          "attributes": {
            "POSITION": 0,
            "NORMAL": 1,
            "TEXCOORD_0": 2
          },
          "indices": 3,
          "material": 0
        },
        {
          "attributes": {
            "POSITION": 4,
            "NORMAL": 5,
            "TEXCOORD_0": 6
          },
          "indices": 7,
          "material": 1
        }
      ]
    }
  ]
}

I recently (or I guess not so recently now 😅 ) used treebox to do some geometry node tree generation that resulted in vertex groups... but I didn't see the groups show up in the gltf file. I ended up using materials applied to the groups to add components (that I then used to swap the material for a custom Bevy shader for bark/leaves). Note that there is still a material associated with these groups above.

[ChristopherBiscardi]

oh also, can you provide the use case that you're labelling vertex groups for? It helps when producing test cases and such.

[mholiv]

oh also, can you provide the use case that you're labelling vertex groups for? It helps when producing test cases and such.

Heyo! Sorry for the delay. I thought I had responded, but I didn't lol. My main use case would be to manipulate the vertexes in the mesh(es). For example stretching out the "legs" of a belt so I can have different height legs, but a level belt surface on uneven terrain.

[ChristopherBiscardi]

There's some prior art for exporting vertex groups in the gltf exporter repo: KhronosGroup/glTF-Blender-IO#1232