MaterialX / glTF / USD material interop

Community USD
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Continuing the discussion from SIGGRAPH 2023, Open Source Days 2023, etc. Sessions Round-Up
which mentions GLTF, MaterialX, and USD in the presentations:

I’m curious what the thoughts are on maintaining this “triplet” in terms of materials, as there can be any or all of these bidirectional transfers occurring depending on workflow:

  1. USD ↔ MaterialX
  2. USD ↔ glTF
  3. MaterialX ↔ glTF

I’d assume you’d want each to be as lossless as possible and kept in sync as much as possible.

Thanks,
Bernard

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USD can encode more than MaterialX can encode more than glTF. So if there’s a glTF MaterialX file, you could losslessly

gltF → MaterialX → USD

There’s talk of adopting MaterialX into glTF but until such a thing happens, the reverse direction, USD → MaterialX → glTF is strictly a narrowing.

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Three.js already has a MaterialX loader. A MaterialX extension for glTF sounds exciting! Could that make glTF useful as an editing format more so than just transmission?

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You might want to keep an eye on this extension proposal which could feed into ThreeJS shader nodes (or other node systems). Graph editing ability has been stated as a requirement.

This will also minimize narrowing as adherence to only using “standard” MaterialX node definitions is also a requirement.