Weekly Recap 9

Jason
September 21, 2022
recaps

Weekly Recap #9. This week I’ve found myself needing multiple UV sets on geometry to be used in various ways. I’ll show how to set this up in Houdini and talk about one use case in Touchdesigner.

I’ve never minded doing UV work, lots of folks hate it, I kinda dig it. I also may be alone, but I love Houdini’s UV tools. Here I’ve got my geo with it’s default UVs. I need a uv set where each island is basically as large as it can be within a single tile… overlapping is ok.

One more UV layout SOP tip. To have one island per UDIM tile, with no UDIM attribute, set the target to any attrib. In this case I’ll use the class attribute I already have. Only trick is the layout sop doesn’t like 0 values on the attribute you pick, so offset your class attribute by 1.

Also, a handy bit. This drop down in the UV viewport will let you select which UV attribute you’re viewing. There seems to be a bug in the version of 19 that I’ve been using where only the default UV set shows, in 18.5 it works fine, haven’t tried 19.5 yet.

Now to export. FBX has been the best way I’ve found to carry multiple UV sets across programs. In TD the order of your UV attributes can be important depending on the intended use. I need my overlapping UVs first, then my main UVs second. I use an attribute rename to adjust this.

In Touchdesigner lets look at a simple use case for this. Bring in your FBX, drop a light, camera, and a Render TOP. On the render top change the render mode from 2d to UV unwrap. You can select which UV channel the Render TOP will unwrap to with the dropdown.

Now lets bring in a single piece of footage that we’ll assign to our stones, but we want to use the overlapping UVs for this assignment, that’s why it was important to have the overlapping UVs on channel 1.

Now we’ll use the UV unwrap render as a texture for our model, using the main UV channel for assignment. For simplicity sake I’m bringing in a new piece of geo with only the main UV layout for this.

A bit of a long way around, but on my current project I’m constantly needing to add in video as a texture layer to these large stones. Being able to use a single texture and have it wrap the geometry different ways based on alt UV layouts has been very helpful.