Winding and Normal Maps

fade1

i have a problem regarding the winding of uv's, when mirroring normal maps. usually the reversed winding(=flipped uv's) is fixed by the shader in the engine, so the normal maps render right on both sides of the model.
the hardware i'm working on does not support this. is there a way to fix this? the only solution i have in mind is baking the normalmap to a uvset without overlapping uv's, so no flipping is needed? maybe someone had a problem like this before and knows a workaround.

almighty_gir

have you tried offsetting one side of the mesh's uvws?

Bal

I'm pretty sure this should be software specific, not hardware, just have to find the right programmer to bother until he fixes it in the engine you're using.

fade1

@Bal
the problem can't be solved with the shader. it's the hardware we are working on.(a console...) the manual stats that uv winding order needs to be clockwise. if not the normals will render upside down.
i just have no clue how i could use mirrored uv's then, as the winding order will always be wrong.

Bal

Strange limitation, what console is it? New PSP or 3DS or something?
Even if it's a hardware limitation, it still feels more like a programming problem than a 3d artist one, if there is a solution it's most likely a hack in the code I'd think, have you talked about it with the engineers where you work?

Quasar

Might be a dumb question, but did you mirror your geometry after projecting your normal map? That would definitely cause this problem.

malcolm

We just went through this exact same issue, I think it was the export step that needed to be fixed not the shader, ie the pipeline was not forcing the correct winding order when the mesh was exported out of maya. In the attribute editor of the mesh you have a rollout called tangent space in there you can turn on left handed and ignor and that should fix the issue in the maya viewport. That's how we figured out it was mesh formatting issue and were able to fix it in the pipeline export step.

fade1

We've had some research on the whole problem and to close this thread here are the results:
The gpu of the console(a new handheld) we're working on, can't handle winding problems.(The problem is that the gpu does not store the pointing direction of the vector, as far as i understood). There is no solution in maya(or any other software) to fix this.
Code could fix this for unskinned vertices and even then the performance would drop more as by using a twice as big normalmap. For skinned meshes there is no workaround.
So thanks for the feedback.

Numerator

The other alternative is to double the vertex count and to specify the tangent space explicitly.