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Workflow question for low-poly assets

ZBrush Usage Questions
#1

Hi, I’ve been using Zbrush for about 3 years, but I must have missed something obvious as I’ve never solved the following problem.

I’m trying to model a worn tabletop using a 6-polygon cuboid as the geometry (for use in unity) and a normal map to hold the detail. Being a large, flat object, the tabletop has 2 very large sides (by surface area) and 4 much thinner sides. If I export a simple 6-sided cuboid from 3DS MAX, then subdivide this in Zbrush, the thin sides end up with way too much detail, the large sides don’t have nearly enough.

What is the conventional way around this issue? Is there any way to subdivide this irregular cuboid into even squares and then bake a normal-map down to the 6-polygon geometry?

#2

You could import it with uniform squares. Sculpt, then retopologise it back to the simple form?

#3

Uniform quads is probably your best option like Robb Gordon said.

You could also try to NOT use support edges and use Creasing in Zbrush instead. With a simple box it would be very easy to retain your crisp edges.

#4

Retopology is a major player in my workflow for sculpted game assets. Basically do whatever you need to do to get your highpoly mesh, and then build the low poly mesh around that (which wont take long at all with only 6 polygons… I probably would recommend adding a few more however)

#5

thanks for the replies, in the end I divided it up into more even squares before sculpting. The main thing I still don’t have a good solution for (inside zbrush) is transfering the details from the high-poly mesh to a normal map for the low-poly mesh.

This is because the “z-brush solution” for this seems to be to append the high-poly mesh as a subtool to the low-poly mesh (or vice-versa), then subdivide the low-poly mesh, and use the “project all” button to transfer the sculpted detail (then baking the normal map).

But this process doesn’t work very well for uneven geometry (where some of the polygons are much bigger than others) for the reason I described below. I take it most people just use xNormal to do this, but I can’t believe there isn’t a way to do it inside zbrush.

#6

The problem you’ll run into with normal maps in zbrush is that there are many ways to bake normal map data, and there are many ways to render normal map data. Even between autodesk programs, something like the tangent basis can be calculated differently (and then there’s all the non-autodesk 3d programs and game engines). So it could spit out a map that looks perfect in one program but bad in another.

There’s not going to be a baking solution that will work with every thing, so the next best thing is to have something like Decimation Master and GoZ which will let you easily send the model out to another program so that you can take care of it there. Xnormal is a good choice as it can handle large meshes, you can download custom plugins to control which tangent basis is used (and the July 2012 UDK release should now be synced to the same basis), and it can read exported polypaint data.