Regression: shader discovery returns NdrNodes instead of SdrShaderNodes

[JGamache-autodesk]

Describe the bug
Prior to PR #974 the shader discovery parser was returning SdrShaderNodes. It now returns NdrNodes, which are considered legacy by USD. See PixarAnimationStudios/OpenUSD#1836 for details.

To Reproduce

Expected behavior
Revert the NdrArnoldParserPlugin changes found in #974 while still making sure the results are sane.

Screenshots

Used Software Versions

• Arnold: latest
• USD: 21.11
• Compiler: As shipping with MtoA
• OS: Windows

Additional context

[sebastienblor]

I'm seeing in the comment that the reason to switch to NdrProperty was because some attributes needed by Arnold were not supported through SdrShaderProperty. It says "some attributes like 4 component colors", does it mean that RGBA attribute won't be supported ?

[JGamache-autodesk]

color4 from MaterialX is currently handled as if it was a vector4. Problem is known and a fix was submitted which introduces a Color4 type and fixes the MaterialX discovery.

[sebastienblor]

ok good to know. I'll try to make it work as a vector4.

[sebastienblor]

@JGamache-autodesk there's a PR in #1182 , but I cannot set you as a reviewer. Do you think it's ok ?
I'm not seeing any issue in my tests, even with shaders having RGBA parameters. The original PR had lots of changes,, but I suspect this specific change was meant for materialx. Meanwhile we decided to change our strategy for materialx, so maybe this won't be a problem anymore.

[JGamache-autodesk]

Code look OK to me. Definitely fixes the issue. Thanks.