VRay user color question

[Dubbie99]

Was trying to figure out how to get a Cd attribute to work with a VRay User Color shader on a packed object.
It turns out that we needed to change the Attribute Priority in the VRay User Color params from "User Attribute" to "Map Channel".

This is not very intuitive. We only discovered it by accident. The manual is very unhelpful on the matter. I was hoping that someone can explain exactly what is going on with this parameter?

Thanks!

[glacierise]

Hm, I haven't seen that. Do you have both packed and unpacked Cd maybe?

[bdancer]

It's better to post the hip file.

[david.anastacio]

Hi Dubbie99,

That is not the normal behavior, the attribute nodes in the shading context never need the priority changed. Check the attributes of your geometry something could be incorrect there.
In the following example I just added an attribute noise to a test dummy, exported it as alembic and pressed render.



Best,
David.

[Dubbie99]

yeah I know this is not normal behaviour.
The object in question was some hair geo.
it needed to be packed to that cryptomatte would work, but as soon as we packed it, the Cd would be the same for every strand. Changing that parameter somehow magically made it work.
I'll try to make a replication scene.
[edit] BDancer, I have emailed you a .hip scene. Sorry I can't post it here.

[david.anastacio]

yeah I know this is not normal behaviour.
The object in question was some hair geo.
it needed to be packed to that cryptomatte would work, but as soon as we packed it, the Cd would be the same for every strand. Changing that parameter somehow magically made it work.
I'll try to make a replication scene.
[edit] BDancer, I have emailed you a .hip scene. Sorry I can't post it here.

Yeah that doesn't sound like a general issue with packed objects like the original post made it seem.

If the Cd attribute is in the points it works out of the box:


But if the attribute is in the primitives the geo needs to be unpacked.

Best,
David.

[Dubbie99]

Sorry should have been more clear.
In my test scene the Cd is in the points, not on the prims. Still only works if you change that param.
I'm not saying it is a bug, more that I just don't understand the behavior and what that parameter is even doing.
Thanks for checking it out on your side. Sorry I can't share my scene publicly.

[Dubbie99]

BDancer explained my confusion to me.

I had a Cd attribute on the packed point that was overriding the Cd on the points inside the packed object.
Makes complete sense now it has been explained to me.

It would be nice to update the manual to explain exactly what the override option does and when you might want to use it.

Thanks for the help everyone.