[Maya USD exporter] Negative values converted to NaNs

[sourimantg]

Description of Issue

When exporting (from Maya) objects that have a PxrSurface shader attached, with a Physical definition of a specular lobe, potential negative values (in the extinction coefficient for instance) are exported as NaNs in the target usd file.

Context: I was trying to make PxrSurface definitions match an existing Mitsuba scene, where in some rare occasions the extinction goes to very small negative values, which should be possible to handle.

Steps to Reproduce

1. Open Maya (2017 in my case)
2. Create a simple geometry and attach a PxrSurface shader to it
3. In the Primary Specular section, set the Specular Fresnel Mode to Physical
4. Modify the red component of the extinction coefficient to a negative value (e.g. -0.1) in RGB [0,1] mode
5. Export to USD

System Information (OS, Hardware)

Windows 7

Package Versions

0.8.5a

Build Flags

[jtran56]

Filed as internal issue #162206.

[sunyab]

Closing this out since this is related to the old Maya plugin which has migrated to https://github.com/Autodesk/maya-usd and no longer ships with USD.