Overlapping/mirroring UVs and Normal maps

JamesClarke

This problem keeps coming back to haunt me and I really need to learn where I'm going wrong as this keeps giving me such a headache.

I'm working on a cooker asset, baking high poly to low poly, modeled in 3Ds Max and baked in Xnormal. I'm limited to 512x512 maps so I crammed my uv space and overlapped/mirrored where I could to save space but each overlapped island has totally different shading/normal values. Each overlapping section has been given its own UV island and unique smoothing groups and all overlapping sections were offset +1 in the uv grid space for baking.

Any help appreciated. Thanks.

JamesClarke

Sorry for the double post. I've been digging around and found something about UV Winding Order. It's about Maya though and doesn't seem to relate to 3Ds Max but the issue still looks the same. If anyone could explain or elaborate on this in relation to 3Ds Max that would be awesome.

http://autodesk.com/us/maya/2011help/index.html?url=./files/Polygons_nodes_Tangent_Space.htm,topicNumber=d0e239582

tharle

if i'm reading your normal map correctly then you've mapped a quarter of the front of the door and then used rotational symmetry to put the map on all 4 quadrants. unfortunately that wont work as you've seen - the way information is stored in the normal map doesnt allow for flipping in that way. if you're trying to save space then you can map the whole door and duplicated it for the other door but the orientation of the faces has to remain the same during and after the bake. (after you've done a normal bake of the whole door compare what you get to what you've got now to see how different they are)

hope that helps

JamesClarke

Thanks for the reply. I'm not exactly sure what you mean so I'll explain what I did here.

I mapped the entire door but added edges to the mesh so I could seperate the UVs into quaters. When unwrapping I broke each quater of the UVs apart and mirrored them respectively so that they fit on top of the original quater. I then displaced them into other UV channels for baking.

I know this does work as I have done it before I just can't figure out what I did last time and where I'm going wrong this time. Here's an example of where I got it working in the past (this works perfectly in UDK).

Eric Chadwick

It should work, but it's highly dependent on the way your target engine's import code is designed, specifically how it handles the incoming tangent space.

Our internal engine handles this situation perfectly, as long as all the overlaps are moved to separate whole-number locations in UV space. That is, the mirrored and overlapped UV islands are all offset from one another, so none of them overlap any others.

I think UDK however only handles mirroring on U. There's something in UDN about this.

Ace-Angel

Did you put the Normals/Face after the bake or before?

JamesClarke

Thanks for the replies. I'll take a look around UDN.

@Ace-Angle, not sure sure what you mean. I offset the overlapping UVs before the bake if that's what you're asking?

Eric Chadwick

Some past threads about this issue, here's one, might help...
http://www.polycount.com/forum/showthread.php?t=76636

Dismembered

When baking are you baking with all of your LP visible? It kind of looks like you are trying to bake just parts of your LP visible and the normal information isn't getting interpreted properly across your seams.