View Full Version : Normal Map with UV overlay

07 July 2007, 07:02 AM
I just read the book "Character Modeling 2". I have noticed the UV for their left and right side of the character (from Gear of War) is overlayed. So one of the UV is actually reversed (either right side or left side). From my experice, if UV is reversed, then the normal map will be reversed as well (so things that are supposed to come out will go in). Is there a specific function in 3D Max to fix this problem? If there is, does Maya have this function as well?

07 July 2007, 12:01 AM
It's a very tricky subject, in Max you should be able to mirror UV's and have the normal map render correctly. The renderer is cappable of detecting reversed UV coordinates and it does the inversion on the normal map so everything renders correctly. In terms of game engines, several are cappable of doing this, usually it's the older game engines that will give you trouble.

Usually I have my character setup as usual and have one half of the uv's crumpled up into some corner. After I do the projection, I discard the half of the model that has the crumpled UV's and mirror the good side over and weld it together. It should come out perfectly seamless and only using half the texture space.

I've had some problems getting flipped normals working in Maya, but I do think it is possible. I've looked around a bit but I wasn't able to find any good info on how to get it working properly. I'm primarily a Max user so I haven't looked into it that deeply, perhaps someone more familliar with Maya can shed some light on this subject.

07 July 2007, 03:22 AM
Thanks a lot. Those are helpful informations.:) :thumbsup:

07 July 2007, 05:36 AM
The short answer is that you can get away with mirrored uvs in some situations. I use maya, and if you do high quality rendering in the viewport, it can handle mirrored normal maps perfectly. However, mental ray and maya software render can't. Which means you can't really render them without them being reversed. Pretty much all current game engines can handle mirored normal maps fine, which is why you'll see them in games.

If you want to get away with it in Maya, one workaround is that you can reverse the normals on the other side, which will fix the normal for the render. However, a black seam will show if the verticies are merged together. So you wouldn't want to split a character in half because you'll have a huge black seam down the middle. but if the object is separate, the seam won't show. For example, on a recent character I did, I had a woman wearing a sleeveless dress. I didn't mirror the dress, because it was one seamless piece, but I was able to mirror the arms and legs because they were separated by hard edges. A lot of times you don't want to mirror the torso and main pieces like that anyway because you want to be able to have wrinkles and stuff thats not symmetrical.

Another note is that you won't be able to generate AO maps and bake them to the texture easily if the object is mirrored because maya won't generate the map correctly. You might have to delete the mirrored pieces temporarily to bake the map.

07 July 2007, 06:07 AM
Great advice. Texture space is of the utmost importance. I recently learned the same method of rendering AO and saving space.

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07 July 2007, 06:07 AM
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