About ray differentials of primary rays

[shiqiu1105]

Hi,

I am writing to ask about the ray differentials for primary rays if they don't hit anything.
I still need the differentials info to sample environment map, but how should the differentials be calculated?

Thanks

[beason]

Pixel solid angle, or a fraction thereof?

[shiqiu1105]

Maybe, not sure how the math works.

I think it should depend on the fov, film resolution.