I'm interested in Houdini's glTF exporter. It doesn't seem to be available on Apprentice (?) which I'm currently on to learn it. Nevertheless a question popped up for a possible later use:

The documentation says Houdini can export “custom attributes” to glTF: http://www.sidefx.com/docs/houdini/nodes/out/gltf.html [www.sidefx.com]
I assume “custom attributes” in Houdini refer to parameters that can be created for each node in the parameter interface editor.
If that's correct, how do they get saved to glTF? Does Houdini save out custom attributes in the “extras” of a node in the glTF?

(About glTF extras see the official specs https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#reference-extras)

In order to test it with the glTF importer (available on Apprentice) I externally created a .glTF file with “extras” as key/value pairs in both a root node and in the glTF “primitives” section of a cube. Expecting these “extras” to appear as custom channels in the editable parameter interface after import in Houdini, I was disappointed. I can’t seem to find these custom attributes at all in Houdini - although the import of geometry from glTF works fine so far.

The documentation says the Houdini importer node can import attributes from glTF “primitives”: http://www.sidefx.com/docs/houdini/nodes/obj/gltf_hierarchy.html [www.sidefx.com]

I'd be glad if you could shed some light on this feature and steer me to the right direction!

In houdini, parameters are not called attributes like in Maya. Attributes refers to actual data stored on the geometry. It would only be visible in a geometry inspection tool such as the spreadsheet. Parameters are editable values that control what tools do. They are never exported/imported along with geometry.

Thank you for your reply and explanation about the difference between attributes and parameters! This clears things up a lot for me.

Moreover I can conclude Houdini doesn't currently support glTF extras for additional key/value data per node…

Glad to help clear up some things. Sorry if I'm a bit ignorant on the specifics of glTF support in Houdini. I'm sure SideFX would be interested to hear requests for improvement from users that are using the format.

https://www.sidefx.com/bugs/submit/ [www.sidefx.com]

Thanks for the hint, I'll definitely send a feature request!

There's a Extended GLTF ROP by ToniMacaroni: https://github.com/ToniMacaroni/HoudiniGLTFExtended [github.com]

I've made a pull request that solves build errors for Houdini 20-21.0+, adds install/build instructions: https://github.com/ToniMacaroni/HoudiniGLTFExtended/pull/1 [github.com]

My updated repo fork: https://github.com/animgraphlabgames/HoudiniGLTFExtended/tree/houdini-21-support [github.com]

Everything seems to be working based on what i've tested. Meaning mesh/nodes extras {...} was added to a .gltf/.glb files. Check pull request for more info.