Roy Nieterau

I just wanted to remark something that came up on recent USD-Asset Workgroup meeting:

Note that Variants in USD can not be animated over time. A single USD stage cannot author e.g. timesamples for variant selections and thus within a single USD file it would be impossible to say animate the LOD variant of a prim based on whether it would get closer or further away from the camera.

This by itself makes Variants a bad candidate for those uses of LODs where it would switch dynamically.

You could always write a USD per frame and render that instead - but I just wanted to mention that it might give you problems in certain cases.

What the "recommended" workflow was instead for switching LODs dynamically didn't really find a definitive answer in that meeting if I recall correctly - so I'll leave that to others to answer. Just wanted to highlight the potential issue you might face in the future.

As far as I know in USD itself there's not really such a thing as cross-referencing between Shaders/Materials like a master material. In Houdini itself however, you can of course just create "reference copies" of Houdini nodes so they reference the parms of the others, except for those you want to tweak.

In USD with most renderers what you could do instead is putting down a node that reads a particular user data from a primvar on the geometry. E.g. you could read a filepath from a mesh attribute and use that for the texture, or use a float value from the mesh for specular - etc.

This works fine with Arnold materials. Quickly trying Materialx here with string values doesn't seem as trivial, see attached.

Maybe this gives you some ideas for general approaches.

For me - whenever I use a Transform LOP whenever you customize the `primpattern` parm (Primitive Pattern) at the top then it automatically adjusts the pivot point to the center of the selected primitives.

Note that this occurs when you CTRL+CLICK on the right hand side arrow next to the Prim Pattern field and then select objects in there, and click apply.

I've reported that as a bug since it's really annoying that if you've already done transformations and just want to include an extra primitive that suddenly the pivot changes. However, it does mean that for now that's an easy 'hack' to force the pivot point to bounding box center.

In my bug I've basically requested to implement something like the LOP transforms, so that there are explicit buttons in the UI to "Set the Pivot Point to center" (instead of dynamic evals, etc.)