Static Ray Path Index
A seed random value which is assigned to a ray when it's initialised, and carried through its entire path. This would be useful for things like dispersion, where we could use the value to pick a wavelength used through the entire path.
This differs from using position for white noise as each bounce the path makes, it would return the same value
3 Comments
This could be a very good idea for dispersion. Although, I can't think of other use cases and wonder if perhaps a vector IOR being added to nodes using refraction and then the render engines blending smoothly between those for other "wavelengths" (blender does not use actual spectral data) to allow dispersion by default.
Also, though I would imagine ray index would computationally faster, perhaps ray "wavelength" would be good, so you could actually take the wavelength and map it to the correct IOR.
I think it'd also be useful for some shader optimisation things like ray depth in a displacement shader. assuming the index increments per ray instead of being random you could do less steps early on and increase the fidelity of the shader the more samples you do.
You can already get a ray depth output from the light path node