Feature request in vray mtl

[Neilg]

Working in a very reflective experience space with lots of mirrors, and in order to have good control in post production, I need a set of multimattes rendering where all of my reflective materials are set to 'affect all channels' - that way when I tweak the color of an object, it tweaks the reflected version too.

However - this decimates the raw light / reflection etc passes and makes them useless, and I also need a set of multimattes that are object only to cleanly isolate the objects doing the reflecting (instead of also capturing reflections of those). So right now I have to render every image twice to get what I need, and a feature could be added that would mean I don't have to do this.

The feature request would be a new addition in the affect channels drop-down, so we would have:
Color only
Color + alpha
All channels
Duplicate multimattes (or some better name)

What the last one would do is take any multimattes in the scene (eg 'multimatte obj01') and render an additional 'multimatte obj01 ref' (or whatever you want to call it) as if 'all channels' in the shader was being used - so both are created. The light pass and other elements would then ignore this and render as if they're set to 'color only'

I am aware this would probably increase render time like setting a light select to 'full', but right now the only way to get what I need is to render every image twice and it's really messy. I am now doing some animation which is a real pain in the ass to control - attempting to render the second pass with lower settings is producing visible artifacts because it's not all clear/sharp mirrors.

[Joelaff]

You may be able to do this with LPE.

Not sure, though, as enabling the affect all channels does fundamentally alter a number of channels.

Would be a nice feature to have.

Would be nice if the Multimatte elements themselves had an option to be affected by reflection and refractions (independently or together of course). This way only the objects or materials we want as mattes (as defined in the multimatte element) be affected.

[hermit.crab]

Another solution is indeed using LPEs as Joelaff mentioned. The following expression should include objects with a certain LPE label and all of their reflections:

(C.'obj1'.*)|(C<R[GS]>.'obj1'.*)

It should work regardless if "Affect All channels" of the shader is active. You can keep a multimatte to mask out the objects and leave only the reflections or you can do two separate LPEs - for the objects:

C.'obj1'.*

For the reflections:

C<R[GS]>.'obj1'.*

[Joelaff]

Oh, cool! I need to play with this, if it works without affect all channels. I was hoping it would chime in hermit.crab because you seem to be the resident LPE master.

Thanks.

Now if we can just get LightSelects (and thus LPE) to work when Light Mix is enabled then we could do this much more easily. I have requested this before and matanov seemed receptive.