Mirroring uv's in the normal map inverts lighting in UDK?

malcolm

Hey so this isn't a problem in Maya or any other engine I've worked in, but in Unreal when I mirror a section of my uv's once it's in the editor the lighting appears inverted on the part of the model that has mirrored uv's.

What's the official fix for this issue, I would imagine I could flip the normals on that part of the mesh, but surely that's a hack and wouldn't that cause issues for lighting as the vertex normals would be pointing the wrong way?

Vysuki

When I mirror a section of the mesh I shift the mirrors UV's along one tile. That always solves my issue with seems in udk. I'm not sure if this is the official fix but it works on the meshes I've done.

Obscura

Unfortunately this is not always working.You need to mirror your model on a non tangent surface. Like -I- not /I\ . I hope you understand what i am talking about.

malcolm

Obscura, I'm not sure what you mean.

Vysuki, I don't have a seam, I have inverted lighting, my mirrored uv's already exists on a separate tile offset by -1 for baking purposes.

I did some more tests inverting the normals on that half of the mesh actually does not fix this issue. The only thing that fixes the issue is inverting the green channel of the normal map, but this of course inverts the other half of the model. I also tried overlapping the uv's so they both reside in the 0-1 space and this does not help.

See image below, this is all in Maya, but it shows the issue I'm having in Unreal.

Obscura

I tried a few test , and i got this problem in unreal, when i moved the mirrored uv part to u1 but didnt flipped this part horizontally.Sorry for the previous tosh, I just remembered, someone wrote this here when i started a thread about this problem.

Froyok

Try unchecking the "tangent" setting of your static mesh when importing it in UDK, just keep the "explicit normal" setting enabled.

I suggest to look at these thread (and to read everything) :
http://www.polycount.com/forum/showthread.php?p=1777252#post1777252
http://www.polycount.com/forum/showthread.php?t=116474

malcolm

I untick anything to do with unreal generating the normals for us and use the normals directly from the .fbx that comes out of Maya, is that what you mean?