Lens shader and PBR

[henderthing]

If this has been covered--I couldn't find it.

I've developed a stereo lens shader for Arnold, and have replicated its functionality in Houdini--almost.

I'm using a grid in front of my ortho camera, transforming P to NDC and driving all of my math from these values. I am using "Refracted Light" VOP in my surface shader to fire rays from an origin that I've computed in a direction that I've computed.

All is fine and well when using Ray Tracing--although I was a bit surprised to find that [0,0,0] P ray origin in this context is actually Camera Origin, not Object Origin.(even though it's a surface shader) That's fine--move grid to -0.1 in Z and Camera to zero and all is well.

When I started working with PBR, I find that I cannot change the Ray Origin using "Refracted Light." No matter what I do, the ray origin is geometry Surface P.

I can get close to the proper results for non stereo if I use a tiny, tiny grid and ortho plane size--but this will never be exact and makes me feel dirty. Furthermore, I need to dramatically alter the ray origin across the image plane for any stereo application of this shader.

So--three questions:

- How can I exert this control over ray origin in PBR? (direction works fine)

- Is there a way to detect the renderer being used from within the shader? (like I said--PBR and RT behave very differently)

- Will we ever get the capacity for creating proper lens shaders for Mantra?

I'm sure this all stems from a fundamental misunderstanding I have regarding what to do with the BSDF parameter--but not sure how to proceed. Any help is appreciated.

Cheers

-matt

[rsd]

- How can I exert this control over ray origin in PBR? (direction works fine)

PBR shaders not support this opion - VOP Refracted Light uses specular() and cone().

- Is there a way to detect the renderer being used from within the shader? (like I said--PBR and RT behave very differently)

renderstate("renderer:renderengine", string value&)