Issue getting cryptomatte working with vray proxy

[chris_elmer]

I have a simple hierarchy of cubes which I've exported as an alembic from maya. I'm reading that .abc file back into maya with a vray proxy node. My cryptomatte is set to "sub object name" (which I believe should give a working crypto pass with a vray proxy), but I still get a single value for all the geometry in my file. Am I on the right track? Is there anything else I need to do?

Using
V-Ray v6.10.00 and Maya 2023

[hermit.crab]

Pretty sure those boxes are instances, which as stated in the docs, won't receive separate ids with the Sub object name ID type.

[chris_elmer]

Hi, yes I saw that as well. No they are not instances. I've attached a maya file if you want to take a look.

[hermit.crab]

Ok, here's what's going on (it took us a while). It seems that when exporting identical objects, even though they are not instances, Maya exports them as such (no checkbox for this). If you export three random objects in a similar fashion, you'll notice that the cryptomatte is correct. You can fix the cubes as well by disabling instancing in the VRayProxy settings (VRayProxy> Alembic proxy parameters > Instancing > None). This explains why exporting .vrmeshes works as expected, too.

[chris_elmer]

Hey there, sorry just getting back around to this. Thanks for the tip about instancing, that does fix the issue in that example file.

There is a second issue however. If I apply a displacement to the vray proxy, it breaks the crypto and it's treated as one object. And if I subdivide the vray proxy using the subd attributes on the vrayDisplacement node, it also breaks. It's worth noting I can use the vray proxy subdivision tick box, but then I believe I lose the control over view dependent tessellation. I can work around the subdivision issue, but it would be great to sort out the displacement bit.

I've attached an updated example file if you want to take a look.

[hermit.crab]

Hey there, sorry just getting back around to this. Thanks for the tip about instancing, that does fix the issue in that example file.

There is a second issue however. If I apply a displacement to the vray proxy, it breaks the crypto and it's treated as one object. And if I subdivide the vray proxy using the subd attributes on the vrayDisplacement node, it also breaks. It's worth noting I can use the vray proxy subdivision tick box, but then I believe I lose the control over view dependent tessellation. I can work around the subdivision issue, but it would be great to sort out the displacement bit.

I've attached an updated example file if you want to take a look.

This is a known bug (internal bug-tracker id: VMAYA-11744). I'll notify the project manager about prioritizing it.

[chris_elmer]

Great, thank you

[chris_elmer]

And I have to ask... is there an eta for a nightly with this fix? We're in a bind without it at the moment.

[hermit.crab]

And I have to ask... is there an eta for a nightly with this fix? We're in a bind without it at the moment.

Sorry to say, no. Judging by the dev's comment that the issue is more complex than it seems, it will take some time.

EDIT: The following might suffice as a workaround. It is possible to bake the displacement/subdivision to a .vrmesh. Using this method instead should bypass the Cryptomatte issue:

1. Set this piece of code as a Post Translate Python Script (Render Settings >Common> MEL/Python callbacks)

from vray.utils import *

node=findByName('pCubeShape1@node')[0]
node.set('bake_subdiv_filepath', 'C:/Users/Alexander/Desktop/baked.vrmesh')​

2. Replace pCubeShape1 with a geo of your choice. If you are uncertain about the name, export a .vrscene, open it via Notepad, and search for "node" until you find it.
3. Make sure you use "/" instead of "" in the path.
4. Render
5. The .vrmesh should be in the selected folder

Note: It might be a good idea to turn the displacement's view dependent off, and choose a suitable subdiv/edge length instead.