ZBrushCentral

normal map theory: overlapping uvs after Zbrush export

ZBrush Usage Questions
#1

I’m creating game art that is being used in Torque Advanced. I’m really trying to maximize the texture detail in the model, and I’m experimenting with modifying the post-Zbrush tangent-space normal map so that symetrical geometry shares one set of normal information. I realize that to cannot overlap UVs in my model and get good results when exporting my normal map from Zbrush. But what are the problems associated with overlapping the UVs in the model after the normal map is produced?

I’ve noticed in the Gears of War game art, for example, that the halves of faces use the same normal map. But when I try this with my character, the contours on one side of the model are reversed… bumps appear like divots, convex scars appear like concave valleys. Not the effect I was going for.

Basically, I’m creating a dinosaur, and I’m attempting to share the exported normal map between each side of the dino. Is there any way to do this?

#2

i would like to know this too. if anyone can respond with some helpful advice, id appreciate it. thanks

#3

I believe that they generated the normal maps in 3Ds max using the high res mesh from zbrush and/or mudbox.

good question though, I think you’d have to cut your model in half while keeping all the details and uv maps, not sure if that is possible to do or if its the way to go.

#4

A easy way to get around it to use two shaders, one on each half of the model. Then in Photoshop invert the colors of one of the shader’s normal map.

#5

the trick is to detach all the overlapping Uv faces and scale them down
very small somewhere on your uv sheet where there is a hole.You use that
“temporary” set of Uvs for generating your normal map in zbrush.

and then when you load the resulting normal map .psd along with your original
overlapping symmetrical uvs in 3ds max it comes out perfect.

#6

ive just become more confused.

maybe a mini tutorial?

#7

It’s super simple!
But I don’t have time to post images so here is a more complete explanation,
i hope it won’t confuse you more.

here is the situation.
You already made your Uvs.
half of your dinosaur Uvs are overlapping over the other half so zbrush
can’t make a map out of it.You know that.So what you are gonna do is
use 2 copies of your Uvs

-one that overlap and is symetrical that are your real Uvs that you’re gonna use for rendering (your actual uvs)
:let’s call them Real UVs

-and another one that don’t overlap and are used ONLY to make your
normal map in zbrush
:let’s call them "temporary UV’s

1-save copy of your Uvs and call them real Uvs

2-So in the program in which you made your Uvs
(maya,max,blender…whatever)
select the overlapping faces of your UVs (not the model)
and look for an option in your Uv program to detach them (in max it’s called
detach edge verts)
It’s gonna let you move around all the overlapping side
of your dinosaur 's UVs.
Now move it and scale it down so small that you can hide it in a hole
on your Uv sheet.
By a hole I mean a place that isn’t covered with
the other side of your dinosaur.(ex:the hole between two fingers)

3-So now go in Zbrush and use those “temporary” Uvs to generate your normal map .
Zbrush is gonna make the normal map for only one side
of the Uvs and the othe half will look like trash(because it’s scalled so small)

4-Now take the resulting normal map that is in psd or bmp and load it in your 3d program with your model with your REAL UVS on.
Shazam!

It’s a 2 minute operation!

#8

Well, I was able to get it working. For some reason, I thought just duplicating and flipping half the normal map (without overlapping geometry) would work for testing purposes, but I was wrong. That was giving me the reversed contours. It wasn’t until I overlapped the geometry on half the normal map that I could see the normal map being used on both geometry halves correctly.

#9

thank you Christian Michelin i will try that right now :slight_smile: