[material] Add metalnessMap and roughnessMap.

[donmccurdy]

Fixes #2709.

But, maybe this needs more discussion. See #2721.

1. The occlusion in my sample model doesn't actually work until you duplicate the UV channel.
2. The metalness and roughness in my sample aren't visible, but definitely were applied to mesh.material. That probably just means I exported the texture wrong (I suck at Substance Painter) but it would be nice if someone could verify with a known-correct texture.

All in all, mixed feelings about whether these more advanced textures should be in the material component or just left to three.js loaders. Documenting good export processes for well-defined model formats is hard enough. 🙃

metal-rough-cube.zip

[dmarcos]

Could we have at least a working sample as part of the aframe examples?

[ngokevin]

@cvan Why are labels being created?

[donmccurdy]

Could we have at least a working sample as part of the aframe examples?

If we plan to merge this, sure. But mostly I just wanted to add context to the discussion in #2709. Do we want to support this?

[dmarcos]

I don't have a strong opinion. Have we seen much demand besides the people involved in #2709?

[donmccurdy]

No, none actually.

[donmccurdy]

Will close this, and re-open if we come to another conclusion in the issue.

[donmccurdy]

Re-opening. I think it may be better and less surprising to just match the available parameters of MeshStandardMaterial and make this available for users working with OBJs.

[donmccurdy]

Could we have at least a working sample as part of the aframe examples?

I'm inclined to say this feature should be available but not advertised in its own example.

[dmarcos]

@donmccurdy What do we do with this?

[donmccurdy]

I'd vote to merge it, for parity with MeshStandardMaterial. Users could create an OBJ in any program, texture it in Substance Painter, and wire up their metal/rough textures with the material component. So it's a plausible workflow, but not one I really want to recommend or advertise with an example unless people are using it successfully.

[dmarcos]

Thanks!