The full error is: “Getting Group Membership on Packed Instance Part : Invalid argument given: Couldn't find GT attribute for group lookup.”

This when importing a particular asset on Houdini 18.0.499, Houdini Engine 3.3.11, Unity 2018.4.12f1. That is, it happens when I drag the asset into the scene (any scene, including a new empty one). The asset actually appears to load correctly, and everything seems fine, but the presence of the errors means I'm really nervous about actually using it in a production game.

That same, exact asset works fine on another machine, with no such errors. The other machine is using the same Houdini Version, Unity version, etc.

I've tried recreating my session, rebooting, deleting and reinstalling the Unity/Houdini plugin, deleting Unity Library - just about everything I can do. Even creating an entirely new project containing nothing but the Houdini plugin and this asset didn't fix the issue, dropped exactly the same errors.

My best guess is that Houdini has some hidden cache somewhere on my machine that this is breaking, or… something? I don't even know. Help?


I've attached the relevant asset, if you want to try it out. It makes cool skateboard ramps! (I'm making a game called SkateBIRD)

As an added oddity, a previous version of that Houdini tool imports fine, and creates no errors (though the tool itself is incomplete etc). Even weirder, if I drag this one into the scene first, then drag the newer one in? It says “something already defined some of this, redefine?” and I hit yes and - now the new version of the tool doesn't drop the scary errors at all.

So it's like… what the heck is going on here?

Ok, we're kind of tracking this back. One difference between those HDA versions is that she started using packed primitives in places - https://www.sidefx.com/docs/houdini/model/packed.html [www.sidefx.com] - and the error at least seems to relate to those.

If we strip the use of those from the HDA, this works. Are we looking at some weird bug in the Houdini plugin itself, maybe unallocated memory access/etc?

Ok, in the Assemble SOP node, she turned off Create Packed Geometry, and now… it works in Unity / Unity Engine perfectly? On both our machines?

So this thread may have morphed into a bug report? Hopefully the HDAs help someone figure out what we saw, and if it's a glitch in Houdini Engine or not. See attached for the final adjusted version, everything re-enabled, that appears to work fine.