I am currently implementing GPU shaders ddx ddy instructions by examining neighbor rays’ intersection values, be it world space position or texture coordinate at the point of intersection.

For a single sampled, one ray per screen space pixel and square shaped ray packet, I can infer which rays are the immediate neighbors. Of course, this requires the rays to be ordered and not have been re-sorted in some fashion, for example, by same materials.

This approach may not work for other sampling shapes or multi-sampled schemes. If there is a better way, I would appreciate some tips. Guides for the sampling schemes would also be helpful.

Thanks