Author Topic: Blender to Painter - Multiple UVs / UDIM / materials - Whats the right workflow?  (Read 339 times)

Hey everyone! Been liking the software so far, and have gotten to grips with a lot of the basics on some test models (which were all simple enough to fit onto a single UV without issue), but I'm now working on a piece that can't fit onto a single UV without losing a bunch of detail.

whats the recommended workflow when using your own uv unwraps in a non-simple model? I've tried (and succeeded) splitting the objects UVs up into UDIM tiles, but substance will only see each tile as a single material. The solution to this would be (I assume) a baked UDIM material ID map. But this doesn't seem to be a thing (in blender anyway).

I also tried making a UV map for each object seperately, and including all the objects in a single .fbx. This works, to a point, but the materials overlap in substance so it's unusable.

The only ways I can see getting it to work are -

1) Instead of making a UV map for each object, make a UV map for each material. This means when they open up in Painter, the materials don't overlap in the map. However blender isn't set up for this, and I can't seem to get it to work, so it's probably a no.

2) Basically the same as 1 above, except use UDIMS and make each UDIM tile specific to a material (1001 = green metals, 1002 = black piping, etc). This should work, I think, though in substance the materials are shown as 1001 and 1002 instead of being named which is a pain.

I assume 2 is the only way to do this... but it's weird, cos substance says UDIMs aren't recommended to use, because they are less efficient and aren't fully compatible with game engines etc etc.

So... how am I supposed to do it? I can import the model without any UVs, and let substance auto-unwrap it, and it'll work fine. But I'm left with a few bits of dodgy geometry where the auto-unwrap got it wrong, and there's no way to manually edit it. (I actually like the auto-unwrap, it's better than Blenders' smart unwrap for the most part, but it didn't work on one part of this model for some reason (it left stretched/weird geometry)).

I've already looked at the guides and tutorials for an answer, but they all use simple shapes like a box as the example, so it just gets put onto a single UV map no problem.

Little bit stumped. I'm assuming theres an obvious answer somewhere I'm missing! Appreciate any help with this :)

I replied in the discord as well but for others I'll write my answer below:

Until you're able to paint across UDIMs (not yet supported in Painter), they will get split into their own texture sets per UDIM tile.

When working with different objects you must consider them collectively when working with UDIMs. Example. Object 1 takes three tiles and Object 2 takes two tiles (all within the same FBX)

Object 1 has to occupy tiles 1001, 1002, 1003 and Object 2 has 1004, 1005

You cannot separate them or use a different UV channel between them if merged.

Example with just two objects:

You can accomplish the same thing by using just MAT IDs, and the only advantage right now to UDIMs is it is easier to visually set up outside of Painter. Also if you're working in games you most likely would not use UDIMs, but you would use MAT IDs to keep all your UVs into 0-1 space.

Also to clarify, when I said using different UV channels I mean if you join the objects you cannot have channel[0], and channel[1] both get read. Painter will take your first slot. If you have separate meshes in the FBX then Painter uses the first channel as well. So you cannot do something like this:

Last Edit: June 15, 2020, 05:19:01 am