Dealing With Uvs In Zbrush

[andrew-raz]

well, now that i'm finally registered on highend and able to post in here, i thought i would go ahead and ask people how they handle uvs in a Zbrush production workflow. as a personal thing, i'm set in my old ways, and i like being able to set up all my uvs manually, so that if needed, i can always go into Photoshop and do anything i need to. the AUV and GUV tiles, however, are awfully enticing, however, for their ease of use. you can't get much simpler than one click. and as far as the Photoshop issue is concerned, that has been, for the most part, nullified by the ZAppLink plugin.

in my work, i deal with normal maps a lot, and seams in normal maps are generally a bad thing, since they are very visible: it basically causes a bad calculation with the lighting on the surface or something. so in that respect, AUV/GUV workflows would not work well--at least in theory. i've heard numerous reports that the ZBrush normal map generator somehow fixed that problem, and in displaying such normal maps, it seems to be true--so far. the same seems to be true-most of the time--with displacement maps. if you get your settings right, the seams magically disappear.

so what i've settled on, because at the moment i don't have complete faith in the Zbrush-generated uv setups, is pretty much following what Scott Spencer and Zach Petroc have talked about: i create a base mesh with uniform geometry, either in Zbrush or in another program, bring it up to about .5 million polies tops, usually only a couple hundred thousand, export it back into Maya and create a new mesh with animatable topology, lay out the uvs, and then shrinkwrap it. if necessary, then i go back into zbrush and detail it to all ends, and i've been working my way into texturing exclusively in zbrush, but i've been doing some things in Photoshop still.

i'm curious as to what kind of UV workflow other people have, and what kind of production that workflow is good for. what kind of issues come up with your workflow, and how does your team deal with those?

i would like to get input from all fields if possible. maybe we can all even hear something that someone else hasn't heard of.

[scott-spencer]

hey andrew,

welcome to the list.
usually when i am modeling I will set up some prelim UVs just for the sake of polygrouping in Maya. These may even be automapped sections shifted out of 0 to 1. I have not had to lay out final UVs on most projects since the texture artist usually works those while I am modeling/sculpting in ZBrush. Then when I get the final UV layout I will import the level1 mesh back into ZBrush and extract the maps using MultiDisplace.

Using 32bit maps and Mentay Ray I have had no issues with artifacts on UV borders. This is interesting because I revisited models where I had seen artifacts with 16bit maps and AUV Uvs.
Re-rendering with 32 bit the artifacts were gone.

I did do some experiments on a broadcast project with Normal Maps for background characters and we abandoned the idea for displacements because of seam issues. The best solution that was found was a pelting style layout with well hidden seams. This didnt always work out well and in some cases the normal seemed to flip when crossing the boarder. I have heard that these issues are now fixed with the new plugin allthough I have also heard this problem is actually in the shader you are using for the normal map... not sure on the answer there but I would love to get a definitive word.

I have yet to try the Normal map export options from the Displacement Exporter but the tests I did on ZMapper beta several months back were very promising. Not being a rendering TD the vast arry of options available in that upcoming release made my head spin. Just the ability to voew the normal map in realtime and morph it into the indivdual UV islands would have saved hours when working on the formentioned seam issue!

S

[sbroumley]

Not sure if this will help, but when running tests way back in August under REYES renderers like 3Delight and Pixie we had severe issues if the shader rolled normalmaps and displacementmaps together. When we pulled the normalmaps out and rolled them into the surface shader everything rocked. In fact we dropped about 60% of the displacements in the scenes even closeups. This also allowed us to turn on the displacement as needed for effect.

Of course I think it always comes own to project specific needs, no magic solution exists.

[andrew-raz]

does anyone know of studios that use the zbrush UV system then? or does everyone usually prefer to have more control over seams and such?

as far as normal maps, don't quote me on this, as i'm not not a comp sci major, but i believe there's no way around the normal issue. basically, on the surface of the model, the shader considers all 'smooth' normals to be basically that-smooth, then calculates relative normals based on the normal map-"at this uv coordinate, the surface normal vector is this". the problem with the seams is that because the normals of the model are considered 'smooth' by the shader, the relative normals at the seams are facing away from each other, rather than lining up, so it causes a "gap" in the normal calculation, much like it does when setting a hard edge in the normals. in fact, is is the same thing, only it's the shader telling the renderer to do that, rather than the model normals.

so along that line, it really makes sense that a displacement map would would make those seams look even worse; the displacement is actually displacing along those normals, which are separating away from each other.