Hydra Houdini: VdbVolume Shader

[aoblet]

Title

VdbVolume shader has no Houdini node, how are otls/*.hda generated?

Summary

BaseVolume is exposed as a VOP.
But VdbVolume isn't, despite being a distinct, documented shader for VDB-backed geometry (VdbGeometry), not an alias for BaseVolume.

Findings

• houdini/moonray_nodes.json: has BaseVolume, VdbGeometry, VdbLightFilter... no VdbVolume.
• moonray/dso/volume/Vdb/attributes.cc: real, distinct attrs (opacity_gain_mult, color_mult, incandescence_gain_mult, anisotropy).
• shader_json/VdbVolume.json: already has this data.
• houdini/CMakeLists.txt: only installs pre-built otls/soho — no JSON→HDA generator in-repo.

Questions

1. Is HDA generation from shader JSON automated or hand-maintained?
2. If automated, is the generator just not open-sourced?
3. Known gap, or oversight?
4. Preferred way to add a missing shader's node?

Can PR a moonray_nodes.json entry / .ds for VdbVolume once process is confirmed.

[randypacker]

The HDAs were generated by one of our other teams initially and we haven't been good about keeping them updated.

This has been a known gap for some time. We have been making some progress and currently have a script that builds the files, but it hasn't had much testing and we need to extract it from our studio environment before it can be open sourced. Ideally it would become automated and part of our CI or release process, but that might be tricky due to the Houdini dependency. We're actively on this to sort it out.

In the short term I don't think we have a preferred way to add a missing node, but a PR would be welcome!

[jlanz]

We've tracked down the reason for the omission of VdbVolume!

The short version: It was unintentional.

The long version:
At DWA we have another volume shader that we were not able to include in the open source due to deep studio dependencies. VdbVolume was built to replace it for the open source release. The script that we used to generate the files in moonray_dcc_plugins repo originally came from our Lighting Tools Team. To avoid confusing our artists with two volume shaders, they had explicitly skipped VdbVolume.