So I was testing out the new render pass lop and have run into some issues with it.

1. Matte Objects: No matter what primitive path I provide to matte objects I cannot get the matte to work. If camera visible is left to / as default then the prims in the matte parm are still always visible. If I limit the camera visible prims I also get no holdout.

2. Collections: I know this is making collections to do things with at render time but I find that particularly with large scenes with many primitives we build collects using the collect lop to make it easier to make changes such as matte objects or removing camera visibility to many things at once, but though I see the collection added to the renderpass primitive collection when enabling the render pass in the viewport I never see the contents of that collection (i.e. an env collection) work in the viewport karma render (cpu or xpu).

I could definitely be doing something wrong but this parts of this node just don't seem to be working as expected, or are not documented enough to show what I am doing wrong.

Hey!

I noticed Matte Objects parameter works only with collections and doesn't support prim paths. A bug I assume.

Dawid

Can you send a sample hip that demonstrates the issue in #1? I'm unable to reproduce (based on what I understand it to mean at least).

Looks like I can get it to work if I do your simple example, but even your example doesnt work if you set Matte Objects to /grid1 (the root component of the grid). It works if you give it an explicit path to the mesh. (i.e. /grid1/mesh_0) This seems like a major flaw, shouldn't matte and all of this work so that you could privide a primitive path and all the child prims of it would respect that?

Thanks for pointing that out. Our starting point for applying the Render Pass has been based off of code in the USD repository for RenderMan. That includes, by design, only applying matte data to *geometry* (https://github.com/sideeffects/HoudiniUsdBridge/blob/houdini21.0/src/houdini/custom/RAY/BRAY_HdKarma/BRAY_HdRenderPassSceneIndex.C#L127).

Your suggestion that we should support specifying this at the parent level is sensible, especially given that we support this when using the Render Geometry Settings LOP to set the matte flag.

Can you please log a bug/RFE for this? I won't be able to focus on this today, and I don't trust myself to remember to come back to this otherwise

I believe I logged it the other day before I saw your reply

hernehill
I believe I logged it the other day before I saw your reply

I had a quick scan of the bug database and I don't see anything. Do you have a bug ID?

As @robp_sidefx mentioned; the matte collection works on geometry prims only. So you need to set the expansion rule to "expand primitives" to correctly apply matting to prims under the specified parent prim.

There are some other tricky things too, like with the prune collection you can't exclude a child from a specified parent like you can with the prune LOP.

I have a tutorial covering it in depth but haven't had the time to finish editing it. Hopefully I'll get it out soon.