MaterialX (https://materialx.org/ ) is a node graph based way to author the surface characteristics of 3D models. It also has shader code generation capabilities for GLSL(OpenGL), MDL(NVIDIA), OSL(OpenShadingLanguage) and MSL(Apples Metal). It was created by Industrial Light and Magic for the new Star Wars trilogy and allows them to abstract the shader definition from the rendering backend. E.g you have the same shader for real-time and offline renderers.
OpenPBR is a shading model (or more accurately a BSDF https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4930030/ ) within MaterialX. It’s the successor of shading models from Autodesk and Adobe who combined their work to make one consistent one.
MaterialX support across the industry is growing. Multiple renderers support it, Blender has a PR in progress courtesy of AMD, Apple use it for their shadergraph for VisionOS development just to name a few.
Together this means there is a lot of alignment between these models. I wouldn't be surprised to see a glTF 3.0 that adopts the OpenPBR as its main material definition, skipping the current extension complexity.
OpenPBR for material exchange combined with MaterialX for shader graph exchange combined (https://materialx.org) with OpenUSD for geometry and scene graph exchange, means together we are headed into a world where high quality 3D assets are exchangeable between content creation tools.
Edit: removed mention of subset/superset since his post corrected the typo
But yes there’s overlap as there will be in any PBR definition and I think the glTF spec can be considered a subset of this, closer to the preview variant.
