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Rendering with Arnold in Houdini and Solaris using the HtoA plug-in.
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Collection Operator - HtoA

Message 1 of 6
327 Views, 5 Replies

Collection Operator - HtoA

Good day,

I've noticed that the HtoA "Collection" operator Selection field is set and locked to "String" rather than say "Operator List" this means that artists can't drag& drop into the selection field?

The management of this "Collection" node is also lacking. A general use case would be use expressions to collect assets in the scene and do overrides with Set Parameter.

For example: If there are 1000+ assets in the scene, but 50 needed to be individually selected and added to a FG layer/pass this would be very un-intuitive for artists to control

ie. *rockA* *plantB_01* *plantB_02* *pebbleC* *plantD* 50+ times.

Likely the artist would at least want to select the assets in the viewport / scene and drag&drop into the selection field?
Either way, once it's there it would also be difficult to modify later. There should be a "list" view in which assets can be easily added and removed.



Maybe I'm missing an easier way to intuitively control "Collections" ?

Thank you,

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Message 2 of 6

Right, the Collection node is a basic UI, and the Selection field supports the Arnold operator selection syntax

We want a better UI for operators (in all DCCs) but there's no ETA on that.

// Stephen Blair
// Arnold Renderer Support
Message 3 of 6

Ok, thanks Stephen! thumbs up.

I guess most users in the future would likely use the "composed scene graph" in Solaris to manage the "grouping" (using said grouping for selection expressions) which would kind of make the Arnold Collection node somewhat redundant.
But let's see what happens!

Message 4 of 6

As Stephen said this is something we'd like to improve but you can avoid repeating things by referring to collections (either in another collection or in e.g. a set_operator selection) using the # notation (see, where you could have a selection expression #fg_pass.

You can mix collections to create other collections, e.g. by creating a collection with the following expression which uses an exclusion set #custom_collection and not #exclude_selection.

Using drag and drop in the UI is nice and works well in many cases, but if the scene is large or you want something that can e.g. dynamically work across different related shots, then using expressions can also be effective and transferable.

Message 5 of 6

Hey Orn,

Thanks for the info!

Yes, I've done some R&D with the Operators and Expressions.
We do generally use expressions extensively for the reasons you've mentioned, so I am all aboard this workflow concept.
For starters I'd want to collect all incoming assets and allow for interception overrides before render etc. this would be "out of box" setup for artists.

In reality though I've noticed on Production, artists need to do unique selections of multiple assets to override certain aspects per ROP (layer/pass) which here—with the current "Collection" mechanics—we lose intuitive control.

Message 6 of 6

  • No drag&drop UI, like we've mentioned. Or even a "List View".
  • No multiple selection + drag&drop from view port or OBJ context into the selection field (which is locked on "String" mode which I think prevents it?)
  • No way of confirming whether the selection expressions or other operators (such as set parameter) are working as intended until render time?

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