Hello folks,

After enjoying myself immensely shading in Mantra for the past two years, I now find myself in a new Houdini situation: Arnold. Why Arnold? It is one of those situations where multiple vendors are handling the same assets, so my hands are tied here.

Anyway, I have no end of trouble getting Arnold to render my textures. Primitives or existing geometry assets can be shaded and lit, but once textures are added to the mix… nothing (that is they render black as that is the missing textures colour). I must be missing something painfully obvious.

My best guess is that Arnold somehow doesn't automatically pick up the UVs of the primitives or other imported geometry, because if I add a UV texture node to my box primitive, I can get textures on it. But the primitives' native UV layout is lost (or never activated).

So… who can be the man of the hour and point me in the right direction?

Arnold should automatically pick up the vertex “uv” attribute. If it's named otherwise, it might not.

An idea: In your Arnold render settings /Properties/Textures, there's an option to Auto-generate .tx files at render time if they aren't present. Sometime you might have permission issues that won't allow you to write the new files in the same directory where the original files are located. Try unchecking this and Use Existing TX textures, and see if you have more luck.

Also be aware that Arnold doesn't render Houdini's packed geometry, although that doesn't seem to be your problem if you can render untextured geo.

Something to chase down and check out. Thanks.

But I suspect the problem lies in the UVs more than in the textures…

If you want to upload an hip file, I'll have a look.

After much testing and reading of documentation, it simply boils down to UDIM tags. Houdini has its own lovely way to handle UDIMs in its image nodes. The Houdini Arnold implementation doesn't support this. So you need to manually type in Arnold's own UDIM tags <UDIM> into the file name in order for Arnold to read your multi patch textures. So…