Enturely custom primitive or hooking the raytracer?

[DLK]

Hello,

I'm interested in integrating my existing cloud renderer with Houdini/Mantra.

What I need is to somehow hook the ray tracing function, so that when Mantra wants to trace ray through my cloud object, it would call my renderer - with ray as parameter - and my renderer would do all the cloud rendering, for primary and secondary rays. For the primary rays, what I need is that mantra would call my cloud renderer for rays that go from camera to the surface of micropolygons. Essentially, I want to make my cloud object be a new primitive rendering of which I handle entirely myself.

I do not quite know where to get started with this - I see GR_RenderHook but from what i can see it does not let me hook the ray tracing function, just the primary rendering, so that i couldn't make my clouds be visible in reflections. I see GEO_PrimVolume but it is providing data for Houdini's own volume renderer.

What I want to ultimately make is a fully integrated custom raytraced primitive with entirely custom rendering.

I would also need to hook into the light (to let my clouds cast shadows onto native objects), but I think I know how to do this with a custom operator that would be used in the light.

Any pointers would be very appreciated.