Edge weighted sub-d: Modo –> Houdini


I don’t need to get edge weights from Modo into other applications much.
Last time I tried was Modo sub-d with edge weights -> Mudbox (this short sword).
I had some issues with it, but it mostly worked ok (I think I used fbx 2013).

This time around, I have an object I want to take from Modo to Houdini.


I didn’t have the same luck as I did with Mudbox back in the day.
I don’t think Houdini imports crease (edge weighting) info from fbx. I probably could have tried another format, though. Or maybe there is some checkbox I missed somewhere 🙂

In the end, I found another fairly painless way of doing it!

Edge selection to UVs

When modelling in Modo, I usually create an edge selection group from all edges of the same edge weight:


For this exporting trick, having this group makes life easy.
Also, only having 1 set of edge weights helps (i.e everything is either 30% or 0%), since we’d need a new UV set per edge group (more on that later).

So, with all those edges selected, I run the unwrap tool:


Export the mesh with the new unwrap to fbx, and then into Houdini.

Here is what my geometry network looks like (merged the fbx into the scene, and re-arranged a bit):


So what I love about this is that it ends up being really simple:

  1. Split the vertices of the mesh by the uv attribute
  2. Group unshared edges (this gets the open edges that were created by the vertex split, which basically gets us back the Modo hard edge selection set).
  3. Set the crease weight values for edges in the group
  4. Copy the crease weights back onto the non split mesh with a wrangle
    (@creaseweight = @opinput1_creaseweight)
  5. Subdivide

On the “crease” node, I just dragged the value slider around until it matched Modo (a value of 3 seemed to do it).

If I had edges weighted at different values, I’d need to create a UV set for each unique value, and do the vertex split + group + crease for each UV set.


I’m still hanging on to the dream of more companies adopting edge weighted sub-d in games.
Creased sub-d is coming to UE4 someday, so that’s exciting 😛

In the meantime, at least I have a pretty easy/slightly hacky workaround!


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