Can I Bake UV Shell IDs into the alpha of a position map?

parsaiej

Hi there,

I really need a way of storing UV Shell IDs into a map channel. Can it be done, in any software at all? Is there a way for me to write a tool that allows me to do this myself? Thank you! 

Never posted here before, and I know very little about 3D software- strictly a graphics engineer, so apologies in advance for missing anything obvious.

Eric Chadwick

What exactly do you mean by UV Shell IDs? An image or two would help immensely, as well as a use case.

parsaiej

I'm working on a game in which you play as a tattoo on human skin. It calls for a lot of interesting work with UVs.

The picture refers to what I mean by the UV edge, the link goes to a gif showing my issue in action: https://twitter.com/parsaiej/status/786039071873183744

throttlekitty

That's fun! For a Shell ID, you could assign a colored material or grayscale value to each set of faces in that UV shell in any 3d app, and bake them to a texture there or in xNormal. It's common to bake out a Material ID for masking purposes during texturing. You didn't mention the UV edge part in the first post, but that sounds more like a code solution than an art one- though an object space normal map may be of help there.

parsaiej

Yup, I was planning to bake the ID into the alpha of an object space position map Thanks for your help! I'll check that out. So far it has been a heavy use of coding + compute shaders to get the tech working.

Eric Chadwick

I think what you want is decal projection mapping. Here's an example in the game Trackmania 2, skip to around 2:10

parsaiej

I plan to integrate this solution with screen-space decals. The big thing is I need to properly transform dynamic positions withing the UV frame, and ensure that those positions are mapping to the correct UV shells.

Once the positions are properly transformed, I would render the actual tattoos as decals based on those positions.

Eric Chadwick

If you web search for "decal projection mapping" you should find the Wolfire blog and a few other gems, different approaches for similar situations.

parsaiej

Yep I was researching that the other day, I plan on using Wolfire's solution since it works really well with a singular set of geometry.

My unique constraint is the fact that a player moving through UV shells poses a challenge that decals cannot on their own solve, and must be solved in the inverse approach.