How to expose a shader parameter to USD

[ckingT5S5B]

I am trying to create a Arnold Shading network when parameters are exposed so I can use USD composition to set the values. In particular, I want to set the file path for a texture in a USD property on the Material. In a Karma network, I would add a parameter node. I can't seem to find the equivalent for Arnold. I thought user_data_string might do the trick but that seems to just read property values from the geometry. I want to read properties from Material. I attempted also to "promote" the value using a MMB menu, but that didn't seem to have any effect.

Am I missing something?

[julian.hodgson]

We have a ticket to support the promote parameters in order to create user data to check for exported user attributes. This will allow creation of the parameter node, and update the interface on the arnold material builder node. But this would read the property from the geometry as you say.

You want to read properties from the material though? Do you have a simple scene to show what you're trying to achieve?

[ckingT5S5B]

Thanks for you reply Julian.

What I was trying to do in this instance was to create a base material and then create specializations of that material by using USD inheritance and setting a few properties in the derived shaders.

More specifically I am trying to mimic the notion of "Material instances" from Unreal Engine.

Chris King

Pipeline Architect

Spire Animation Studios