Material assignment in 3D models

[ClemensLinnhoff]

Is your feature request related to a problem? Please describe. There needs to be a way to assign a material ID to the geometry which can then be looked up in the OpenMATERIAL mapping table.

Describe the solution you'd like Specify the name of an OpenMATERIAL assignment slot/channel, e.g. openMaterialAssignment

Assignment with a texture:

"openMaterialAssignment": {
    "openMaterialAssignmentTexture": {
        "index": 1
    }

Assignment per mesh:

"openMaterialAssignment": {
    "openMaterialAssignmentValue": [
        5,
        2,
        3,
        7
    ]
}

Describe alternatives you've considered

Specify a suffix for the texture files and look for the same base name as the albedo texture but with a different suffix. But this would only work for textures.

Additional context

Do conventional exporters, e.g. in Blender, support custom channels? Are custom channels like this supported in all the formats (glTF, FBX an USD)?

[ClemensLinnhoff]

I will ask our 3D artist to try this out and create an example.

@drsftx73 might also have time to check this out.

[ClemensLinnhoff]

It is possible to add custom properties to materials (e.g. in Blender):

[LudwigFriedmann]

UV-Mapping for Albedo texture has to be existant in the 3D model and shall be used for UV-mapping of this specific OpenMATERIAL texture

[ipg-sig]

Works with .fbx if you use the Better FBX Exporter AddOn for Blender (looks like a bug in the standard .fbx exporter in Blender) Test_FBX.zip Test file directly exported in Ascii format.

[ClemensLinnhoff]

It also works with glTF: Test_glTF.zip

[drsftx73]

@ClemensLinnhoff can you please post the source blender files as well?

[ClemensLinnhoff]

Unfortunately I don't have the blender file, it was only a quick test during a meeting. But you can just import the glTF to blender. There should not be a difference. All data was exported to glTF without any loss, as far as I see.

[ClemensLinnhoff]

It has to be clearly defined how uv mapping works with the OpenMATERIAL texture.

[ClemensLinnhoff]

We discussed using custom properties and an alternative to put the texture assignment in the OpenMATERIAL asset file. It was decided to use the asset file, because the 3D model file does not have to be changed and different parsers might not support custom properties in 3D models.