MAYA-109893 Integrate 21.05 UsdPreviewSurface shader into mayaUsd plugin

[JGamache-autodesk]

• Leverages recent code in Maya that simplifies Light integration.
• Original shading fragment still present for older versions of Maya.

[JGamache-autodesk]

Brings the Helmet discussed in PixarAnimationStudios/OpenUSD#1174 closer to Pixar's usdView version.
Helmet using original UsdPreviewSurface.xml shader fragment:

Using latest Pixar shader code from UsdPreviewSurfaceNG.xml fragment:

[JGamache-autodesk]

Still missing: Normal maps, as is plainly visible on the air intake tubes.

[JGamache-autodesk]

Here is the gramophone, for comparison:

[williamkrick]

To what extent should I be reviewing usdPreviewSurfaceNGLighting.xml? There is a lot of code there which looks reasonable at first glance, but I didn't try to delve too deeply into it.

The rest of the files are all fine.

[williamkrick]

To what extent should I be reviewing usdPreviewSurfaceNGLighting.xml? There is a lot of code there which looks reasonable at first glance, but I didn't try to delve too deeply into it.

The rest of the files are all fine.

I did some comparisons between the Pixar glslfx file USD/pxr/usdImaging/plugin/usdShaders/shaders/previewSurface.glslfx and the Maya version usdPriviewSurfaceNGLighting.xml and they seem aligned with one another.

[kxl-adsk]

@JGamache-autodesk I see you updated testMetallicResponse.png baseline. I would assume this baseline will be different depending on the Maya version?

[JGamache-autodesk]

@kxl-adsk The result will be different based on the Maya version. I will add a check otherwise the preflight will not work.

[dgovil]

Typo? sef -> set