As the title states, the Mat ID of a vraylight material isn’t working when it’s in a multi sub-object material. So, if you make a multi sub material, and the first material is a regular vray mat, the mat ID will work. However, a vray light material with a different mat ID will not work, it just assumes the same mat ID of the first material.
Using Max 2020 and Vray 5 update 2.
This works for me, but I may have misunderstood the issue. Could you share a screencap of the material setup and result? Or just a simple scene where the issue is present?
This seems to work for me too.
I made a multisub, with the first material a vrayMtl, and the second a lightMtl.
Applied material IDs 1 and 2 respectively (the render IDs, not the face IDs, although they are identical in my scene).
Assigned the material, and rendered with a vrayMtlID and a multimatte REs.
They all seem to get the right data.
As Alex said, could you share more info, or a piece of the non-working setup?
Hi guys,
Thanks for looking into it. I figured out what the problem was. I had an falloff map in the opacity channel in the vraylight material. It was black color for both, I don’t know why I did that. So normally that would have rendered as totally transparent but since I didn’t have “multiply color by opacity” it was showing up in the rendering. But for MAT ID purposes, it was rendering as if it was totally transparent. I don’t know if that makes any sense, but here’s a quick jpeg of the situation. In any event, I just turned off the unneeded opacity map and I have my Mat ID back. Sorry for the fuss!
Glad to know you’re sorted out! 
