Catch-22? The Relationship between my Game Engine mesh and my Subdiv Sculpting Mesh.

Pwwka

I think I'm missing something fundamental here: How do I streamline my mesh (post-texturing) without messing up my carefully constructed UVs?

I construct a base mesh in Max/Maya and export for texturing/HiPoly detailing in ZBrush or equivalent.

This base mesh needs UVs before export so that Poly/vertex painting and Details can be mapped. It seems as though this mesh needs to be locked down in terms of geometry, as removing geometry is impossible without messing up UV layout ("Preserve UVs" in 3DsMax has limited effect). BUT a realtime-friendly mesh (with tris) doesn't have a subdivisional-modelling friendly geometry without changing the geo which, again, scrambles the UVs, sooo...

What am I missing? Is the process as messy as it seems? Obviously this is a fundamental issue, and any help/links would be most welcome..

[I'm aware that UVs aren't crucial in ZB - that Polypaint can be projected in xNormal without UVs, BUT this doesn't preserve straight lines, as projection depends on a cage.]

low odor

Not sure what you mean by this:  "BUT this doesn't preserve straight lines, as projection depends on a cage"

an example would be helpful

Generally you just reproject whatever detail on to the mesh with UVs

here's a way to do it in Zbrush with polypaint

https://www.youtube.com/watch?v=gR0v8dLw77c

musashidan

You don't need to project the polypaint. You just use polypaint to texture function and export the texture.  Apply it to your low poly. Note: ZB uvs are vertically flipped in relation to other software so hit the flip v button before export.

Pwwka

Thank You.

@Low Odor

I never thought of using morph target and projection in this way (would've thought vertex repositioning would warp projected colour).

But the target mesh of the projection in this example has a subdivision-friendly geometry (even poly spread etc) - not a game-ready geometry.

@Musashidan

"Polypaint to texture" requires a sculpting mesh with the same UVs as the game-ready mesh. 

My confusion arises from the fact that changing the geometry (so that it can subdivide) greatly warps the UVs

If xNormal vertex colour projection is the standard method, that explains everything, as the two meshes don't have to share a UV: I will go and do more tests and assume that my problems can be solved.

ActionDawg

I'm unsure of why you need UVs on the high poly at all, and what your end goal is here.

You have at least two different things when following the traditional baking workflow, a high poly model and a low poly model. If you need to paint details on the high poly via vertex colors or either unwrapping it (note though that this is not typical), so be it.

When you want to transfer this detail to your low poly model you simply unwrap it and then bake the high to the low. If you need vertex colors or a textured high poly that's fine, you just load it up.

It's not necessary for there to be any meaningful relationship between the topology or unwrap between the high and the low for you to have a bake. The only goal is to get the shape and volume of the low to as closely match the high as possible without blowing your triangle/vertex budget.

musashidan

I think you have yourself confused. When you talk about the game mesh and the sculpting mesh they are one and the same in a zbrush subdiv levels workflow. Both the lowest level uvs and topology propogate up through the levels.

Yes, subdividing a mesh can warp uvs(linear vs smooth uvs) Zbrush has a smooth uvs function. But that is immaterial,  you don't have to worry about uvs on your high poly for baking....ever.

ActionDawg

I mean, you often want to optimize the final mesh after going through zbrush, especially for specific hardsurface workflows. So to say that the game mesh and sculpting mesh are one and the same is not necessarily true.

As for uvs on a high poly, there have been a number of instances where I've needed exactly that. Particularly when being given a textured high poly asset that was made for other purposes and repurposing it for a game asset, in which case you can transfer the old textures during baking.

musashidan

@somedoggy sorry, I should have been more specific. In the OP's case I'm talking about a basic character pre-made game topology mesh being ported to ZB for sculpting and polypainting (which I assumed from the original, somewhat confusing, post)

Obviously there are more specialised cases, as you've mentioned,  and hard-surface props have a dozen approaches but, for now, the basics.

Pwwka

Thank You very much. My confusion was how to transfer vertex colour to the practical mesh. Of course, Surface Noise, Saving Masks etc will require UVs on the sculpting mesh, but for some ridiculous reason I thought there had to be a direct link between the two UVs - hence the confus/ing/ed question.

 Good Lord, Sweet Liberty.

kanga

Make sure your hi and low meshes are in exactly the same place in 3d space. You can achieve that with G0z. I dont use zbrush uvs for anything other than a detail tool in zbrush itself. If your low poly and hi are in the same place then there shouldn't be a problem. If you are using a 3d app then Goz a decimated copy of the ZB high to the app, match the scale and position exactly, then use a retopo tool to adjust the lowpoly where needed, throw a cage around the lowpoly using the decimated copy of the high in the projection cage settings. Export and bake.

Pwwka

Thank you.
I took all advice on board and the the problem duly morphed: I've graduated to baking problems!