So, these are a few fairly specific workflow questions that I'm hoping someone who has used Houdini in a game production longer than I have might be able to answer. The UE4 forum seems to be specific to uses of the Houdini Engine in UE4, whereas I am presently using it rather more straightforwardly for content authoring.

I would generally be quite happy export .obj files out of Houdini, except that they don't appear to store vertex colour data, or more than one UV set, so for more complex mesh set-ups I'm having to rely on FBX export.

One difficulty I'm finding is that while with .obj files it's possible to stick a File sop into your geo network and cache out multiple assets automatically, you can't do this with FBXes. It's possible to get File sops to output FBX files by writing in a .fbx extension, but this exports them with default FBX settings that are unreadable by UE4. I've been recommended to use a FilmboxFBX rop instead, which does work but I can't see a way to automate exporting multiple files.

E.g. If I set up a For Loop to run through a sequence of OBJs and process them, exporting a separate file on every iteration of the loop, or simply load, process and save a different file on every frame, this is something I can do by caching the OBJs with a File sop but it's not something I can find a way of doing with an FBX rop (best case scenario is it will output everything into a single .fbx with a geometry cache).

Is there a way to trigger an FBX render from within a geo network?

Secondly and even more crucially, I'd like to know if there is any way of exporting FBX files with multiple LOD meshes that UE4 would be able to interpret. It seems like it should be possible to achieve, given that there exist Simplygon plugins for Houdini that must somehow be capable of exporting LOD files. Yet I've not been able to find any workflow discussions that discuss setting up LODs in Houdini besides setting up subdivision detail levels for rendering, which is not quite the same thing.

I've tried loading FBXes exported from Maya with LODs set up, but Houdini does not seem to understand this structure and is therefore incapable of replicating it. It imports the LODs as separate geometries with no understanding of the LOD relationship between them, and does not seem to be able to export them back out as an FBX with LODs.

You can call FBX Rop execute parameter with pressButton() method with Python SOP within geo network.

That way you can automate export similar way how the File SOP works (each time geometry changes python sop will be recooked and triggers FBX Rop). You have to avoid infinite recursion so you can do it by changing display/render flags before and after export. (This is the way how I did it at work).

You can also combine multiple FBX Rops into subnet (in OUT context) and then hit Render button on that subnet. That way it renders everything inside that subnet at once.

About LODs you will do probably best submitting RFE and example fbx file directly to developers: https://www.sidefx.com/index.php?option=com_content&task=view&id=768&Itemid=239 [sidefx.com]

That's brilliant, just the sort of solution I was after! Python nodes make it work just the way I want it to

Hi,
Did you find a way to export LODs groups from within Houdini ?
We're also trying to batch export fbx files with LODs generated in Houdini, but it seems very hard to find any details on how to replicate Autodesk's feature of LODs group in another application.

Cheers

The solution is here:
https://www.sidefx.com/forum/topic/59583/?page=1#post-333638 [www.sidefx.com]
Cheers!