Hi guys,

We're rendering surfaces with V-Ray and volumes with Mantra. I'm trying to make a Mantra LPE to give me the shadows that volumes cast on the surfaces, but not much success yet, any ideas how to write it?

Thanks!

There's no LPE for shadow passes. The shadow pass aov doesn't know who cast the shadow, so it can't be used to just get volume shadows. The only reliable way to get a shadow pass out of any renderer that I know of is to render the scene twice, with volumes as phantom and without the volumes, and divide or subtract the results in comp.

you should be able to render it in 1 pass:
- make your objects fully diffuse, make them not cast shadows
- make your volumes phantom
- include 2 AOVs one of them unoccluded which you can then subtract in comp to get shadow, like: direct and direct_noshadow

or if you want those as LPE's it would be:
direct diffuse: lpe:CDL
direct diffuse noshadow: lpe:unoccluded;CDL
or maybe you can try beauty
beauty: lpe:C.*
beauty noshadow: lpe:unoccluded;C.*
etc...

Cool, I'll try that! Used to do it in two renders but that's taking time, would be great if it becomes AOV.

It's not possible with one render. using a pass without shadows will make it so the volumes can cast shadows in areas where the lighting is already occluded resulting in double shadows.