[TODO] MaterialX support

[syoyo]

Working branch: mtlx https://github.com/syoyo/tinyusdz/tree/mtlx

MaterialX spec: https://materialx.org/assets/MaterialX.v1.38.Spec.pdf (version: 1.38)

Adding TinyUSDZ to load USD model in ASF MaterialXViewer https://github.com/lighttransport/materialx (We can use this as a reference and for verification)

• [ ] UsdMtlx Prim

• [ ] Visualization & rendering validation

  • Plug tinyusdz + MaterialX into pbrlab? https://github.com/lighttransport/pbrlab
  • Use tinyusdz support fork of ASF MaterialX https://github.com/lighttransport/materialx

  • Shading model support

• [ ] UsdPreviewSurface

• [ ] Autodesk Standard Surface

• [ ] OpenPBR https://academysoftwarefoundation.github.io/OpenPBR/ https://github.com/syoyo/tinyusdz/issues/172

TODO

• [ ] MaterialX v1.39 support.

Don't support

• Shaders in OSL, GLSL, etc
  • Support hardcoded shader only

Dataset for USD + MaterialX

• https://github.com/RogerDass/Usd-Mtlx-Example/

[syoyo]

Example syntax(?) of materialx

#usda 1.0

def "bora" 
(
   # Seems we need to specify </MaterialX> prim path
   references = @usd_preview_surface_default.mtlx@</MaterialX>
) {

}

$ usdcat --flatten materialx-001.usda 
#usda 1.0
(
    doc = """Generated from Composed Stage of root layer /mnt/data/work/tinyusdz/tests/usda/materialx-001.usda
"""
)

def "bora"
{
    def "Materials"
    {
        def Material "USD_Default"
        {
        }
    }
}

• Use references to load .mtlx
• Need to add </MaterialX> prim path(otherwise flatten fails)
• It looks Mtlx support in pxrUSD is not yet well supported(material/shader parameter not expanded)

[syoyo]

https://materialx.org/assets/MaterialX.v1.38.Supplement.pdf

Texture nodes

• [ ] tiledimage(for texture mapping)
• [ ] triplanarprojection(for cube mapping?)
• [ ] ramp4

Math nodes

• [ ] place2d
  • [ ] Mapping place2d to UsdTransform2d looses some infos(e.g. pivot)
• [ ] safepower

Adjustment nodes

• [ ] contrast
• [ ] range
• [ ] hsvadjust
• [ ] saturate

Channel nodes

• [ ] extract
• [ ] separate2, separate3, separate4