Transparent Materials in Movie Render Graph Object IDs

Hi devs,

I have been experimenting with Movie Render Graph in 5.7 Preview, and I’m seeing one major flaw with transparent materials.

Both with and without Substrate enabled, transparent materials are not being seen by the Object ID pass when path tracing. I have a graph setup that does a path traced render with 4 object ID outputs - (Material, Full, Material with transparency, Full with Transparency). None of them can ID a transparent material.

Movie Render Graph is so close for us to use in our pipeline in our studio, but this is the one major flaw preventing us from adopting it. The ability to have cryptomattes (specifically multiple of them) work with path tracing in 5.7 is a huge improvement, but the lack of IDs for transparent objects is preventing us from using this until implemented.

Edit: This is also the case with the deferred renderer. No transparent materials present in Object IDs of any type.

@comlys Comparing this same render in Movie Render Queue, you can see MRG is not seeing the same transparent materials. Is this a bug or a limitation of MRG at the moment?

Yes looks like you stumbled onto a bug here. It might be too late for the 5.7.0 release but I’ll JIRA it and the devs will have a look as soon as they can. Thanks for reporting it!

Hey, actually, this is going to make it in for 5.7.

Amazing! Thanks so much for getting this in for 5.7!

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Hello, I would like to ask you a question. You use the Movie Render Graph to output Object IDs. Why can your Nuke successfully recognize them? I use the same way of linking nodes as you do, but my Nuke is always unable to read the object IDs.:grinning_face:

This is in the 5.7 preview build. I had the same issue as you prior to 5.7. I believe cryptomattes were only working in MRG with Lumen renders, not Path Tracer in 5.6 and earlier.