Materials linked to objects (and not to object's data) are not exported

[atteneder]

Describe the bug
In Blender's material tab you can choose wheter you link the material to the data (mesh) or the object.
The benefit (also for the glTF) is that you can instantiate the same mesh with different materials applied.

To Reproduce
Steps to reproduce the behavior:

1. Extract the attached zip
2. There are two blend files with 3 materials on 3 objects each. In omnicase_data.blend the objects have dedicated meshes and materials applied to the data. In omnicase_object.blend the objects share a mesh, but have different materials applied to the objects:

3. omnicase_data.blend exported as separate glTF looks like this:

4. omnicase_object.blend exported as separate glTF looks like this:

Clearly just the material from the meshes is exported

Expected behavior
All materials applied to objects are exported accordingly. The mesh itself is re-used and not duplicated in data.

.blend file/ .gltf
obj_materials.zip

Version

• OS: macOS
• Blender Version 2.80 beta

Additional context
I reported this one in the legacy exporter, where it was partially solved (meshes were still duplicated):
KhronosGroup/glTF-Blender-Exporter#186

[jamespedid]

This would be a great enhancement for my use case :)

[emackey]

I think this issue was fixed in #526, and we forgot to close this issue.

@jamespedid Are you seeing this behavior in the 2.80 release? Or did you just find this in a search? I can't reproduce it from the test model linked above, and I think it's fixed.

[jamespedid]

I think I might have different ideas or expectations and the issue might be slightly different.

For me, I want to create a single model and attach 5 textures to it. I want to export the model with a default texture chosen, but also with the other textures with the intention to change the model to a different texture at a later point in time.

I'm also very new to this technology, so there might be reasons to not do this.

[emackey]

That's an interesting use. Certainly there's been glTF spec talk of materials being swapped like this, see the thread on asset variants here: KhronosGroup/glTF#1569

Nothing like this exists in the Blender exporter as yet. I think you have to use each material that you want exported to the model, but you might be able to use it with object linking as described above. Still there's no way, yet, for the glTF to specify that the app must choose a material, at least until some asset variant mechanism is specified.