uv mirror problems

Shilo · Feb 2012

Hi,

trying to learn normal maps with mirrored uv's. In polycountwiki it said that I should move mirrored uv's 1 unit side so they don't overlap?
What's the reason for that?

In my test bakes I didn't notice anything different and well I had to move them
with mouse and use mk1 eyeball because when I entered 1 on U coordinate with all my uv islands selected, it just flattened them to one vertical line and moved to the edge of uv space..what's up with that?

Thanks for your replys!

Edit: this on 3dsmax!

Eric Chadwick · Feb 2012

You need to toggle the Absolute/Relative button on the far left here, THEN type in your value.

Help: http://download.autodesk.com/us/3dsmax/2012help/index.html?url=files/GUID-C65A1B09-3670-4E7E-BCFC-13E10C83181-516.htm,topicNumber=d28e112516

Two reasons for the offset.

1. To prevent overlapping faces from causing bake errors. This only happens with overlapping front-facing UV triangles, not mirrored ones. But good to do this anyhow because overlapping is common.

2. This depends on which real-time renderer you're using, many do it different ways, but the engine has to create the tangent space for the normal map. Mirroring often creates a shading seam unless the seam vertices are offset in UV space, so they can be given different tangent rotations, which then solves the shading seam. If the verts are overlapping, most tangent space solvers will not create the right tangents. At least that's my non-programmer understanding. :poly142:

Shilo · Feb 2012

Thanks for you reply Eric, haven't tried that absolute/relative toggle yet but I'm sure it works.
Actually I'm now getting that seam in 3pointshader when I baked uv's overlapping.. Will try now your suggestions. Thanks one more time, after
many years in cg and now trying to learn this time consuming game engine stuff with my limited free time I really value replys like your's:)

Shilo · Feb 2012

Damn, moving those mirrored uv's didn't get rid of the seam, it's still there. What am I missing here?

Eric Chadwick · Feb 2012

Did you rebake after fixing the UVs?

leechdemon · Feb 2012

Make sure your geometry is smoothing across the mirrored seam; if there's a seam in the smoothing of the geometry, the normal maps won't be able to fix that.

Depending on what you're modeling, I've found it's best to avoid mirroring UV's on objects that cross your mirror point. For example, when modeling cars, I'll mirror the left/right sides of doors, body panels, etc, however I don't mirror the front and rear bumpers, hood, etc. Anything crossing the middle gets a full bake, and anything on just one side of the middle can get mirrored.

Eric Chadwick · Feb 2012

Yeah, good advice!

Shilo · Feb 2012

Yeah I unwrapped, then mirrored with symmetry, then added unwrap modifier again so I could move mirrored uv's then baked..result (it's a knife of some sorts..)

I guess I should try baking with xNormal or something else..this is max's scanline (mental ray's normal maps are bugged atleast on my installation). Good idea leechdemon, guess I should stay away from these potential seams until I really get this right.

Shilo · Feb 2012

leechdemon wrote: »

Make sure your geometry is smoothing across the mirrored seam; if there's a seam in the smoothing of the geometry, the normal maps won't be able to fix that.

that part has smoothing group? If I understand you correctly $:\$

EDIT:
Now I got it! Weird, I always moved those uv faces that we're generated by symmetry aside, now I selected the original half of the model, moved those aside and now it works, there's still a seam but it's barely visible if at all so I can hide it with some noise on the normal if I really need to..

Thanks a lot guys!

EDIT pt 2:

And now I got another problem, normal map is fine but after I open it in photoshop and save again as targa it shows seam and is pretty much f***** up.. weird?

EDIT pt 3:
Nevermind, baked with gamma correction on heh. Everything works now!:thumbup:

uv mirror problems

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