Cryptomatte support for user attributes on materials

[CopenhagenBombay]

It'd be great if we could get support for rendering cryptomattes using vray user attributes on materials.

[CopenhagenBombay]

This is still a relevant issue for us.

[yolov]

Hey there,

Can you get us more info? User attributes can only be assigned to shapes, not materials, so I'm not sure what you mean.
What exactly do you need to do?

[CopenhagenBombay]

Hey there,

Can you get us more info? User attributes can only be assigned to shapes, not materials, so I'm not sure what you mean.
What exactly do you need to do?

Hi, apologies for the vagueness.

As a feature request, we would like to be able to assign custom attributes to shaders/materials exactly like the vray user attribute on shapes. (Example "attributeA=varA;attributeB=varB")
Alongside an option to render a cryptomatte pass based on these custom shader/material attributes like vray user attribute.
If a custom attribute for shaders/materials is not an option, at least being able to render a cryptomatte pass using the Material ID would also go a very long way.

[yolov]

Can you explain how this will help you? Why do you need it, what do you need to do with it?
What in the Cryptomatte 'by material name' mode doesn't work for you?

[CopenhagenBombay]

Can you explain how this will help you? Why do you need it, what do you need to do with it?
What in the Cryptomatte 'by material name' mode doesn't work for you?

Absolutely. Generally our pipeline has been using object and material IDs for compositing. Making a season of a show the same assets will be rendered over and over and moving to cryptomatte allows us to do a lot using the vray user attribute. (Before we were relying on OID and MID)
The issue with switching to cryptomatte, is the object by name and material by name are not consistent from shot to shot due to namespaces and therefore our compositors would have to redo all the masks for every shot using these cryptomatte passes.
Using vray user attributes, we can make multiple passes that consistently use the same value across all shots and our compositors would not have to redo the masks for these. (We are using fusion and cryptomatte for fusion)
Sadly missing the option for doing the same for material passes leave us half relying on crypomatte and half relying on material ID mattes.

[yolov]

Thanks, it all makes sense now
Does this mean that if Cryptomatte was consistent when the namespace changes, it would solve the problem for you?

[CopenhagenBombay]

Thanks, it all makes sense now
Does this mean that if Cryptomatte was consistent when the namespace changes, it would solve the problem for you?

The issue is we reuse the same assets multiple times in the same scene.
This means we need a way to distinguish between the two instances of the same asset.
Our current solution for this, is we have two cryptomatte passes with vray user attributes, one using the assets name and the second using the assets namespace.
This way one crypto pass selects all instances of FlowerA, while the second crypomatte pass selects singular instances of FlowerA (FlowerA1, FlowerA2 etc..)
And of course we have the normal object and material pass to cover our ass for edge cases.