Good Day.

Can anyone suggest in LOPs how I might use an instance ID in a material. I'm trying to get material variation on each instance of a mesh.

Thank you for any ideas.

lor

Using the materialvariation node set to point instances and the instances parameter to something like /myinstancerprim1[*], you could create a new primvar based on the index variable:
toggle use snippet and set the wrangle to:
value=index

.. which will give you the instanceid as a primvar, so it can be read in your material.

Though probably better for material variation would be to create a color3f primvar already with the desired variation color and just read that directly in your material.

To read primvars in Karma, you can just use a parameter node.

Like Simon said. Here is an example.

P.S. For Karma, you should use Bind VOP rather than Parameter VOP, because inside Mat Lib LOP the semantics of a Parameter VOP is to create an input attribute on the material primitive, while Bind VOP is translated to the standard USD Primvar reader.