Add support for the UsdPrimvarReader_TYPE templates for both import and
export. These are used by several USD test assets and support here
represents the last major piece of the UsdPreviewSurface spec to be
implemented.
On import these become `Attribute` nodes and on export the `Attribute`
nodes will become `UsdPrimvarReader_TYPE`'s accordingly.
Import:
- `UsdPrimvarReader_float` and `UsdPrimvarReader_int` will use the `Fac`
output
- `UsdPrimvarReader_float3` and `UsdPrimvarReader_float4` will use the
`Color` output
- `UsdPrimvarReader_vector`, `UsdPrimvarReader_normal`, and
`UsdPrimvarReader_point` will use the `Vector` output
Export (only `Geometry` Attribute types are considered):
- `Fac` will use `UsdPrimvarReader_float`
- `Color` will use `UsdPrimvarReader_float3`
- `Vector` will use `UsdPrimvarReader_vector`
- `Alpha` is not considered
MaterialX note:
Hydra-native support is a bit more involved and will have to be done
separately. Hydra w/USD sync is trivial to implement but those changes
have been left out here.
Pull Request: https://projects.blender.org/blender/blender/pulls/135143
46ec277713