Face id at each pixel

[gtangg11]

Hey, great repo. Is it possible to modify renderer + add a shader that computes the face id rendered at each pixel? This functionally would make life a lot easier for many downstream applications and allow us to map face metadata to pixel.

I see this is possible for many attributes of primitive already:

pyrender/pyrender/renderer.py

Line 929 in a59963e

if bf & BufFlags.NORMAL: