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Old 13-02-2009, 02:08 AM   #1
jammer_unknown
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Default Strange Normal/bump map problem

Hello,

Wondering if anyone can help me with this. Basically, I've cut my model in half and only uv mapped that half to save texture space, with the intention of mirroring it once textured and everything.

The problem is, when I apply the normal/bump map, the normals on one side of the model are reversed (see attatched file). This only seems to happen once I combine the two halves of the model. I've checked the normals, and yes they're facing the right way, even on the half that's 'bumping' the wrong direction.

I know I could just reverse the normal direction for that half of the model, which works but produces a distinct crisp line/edge/seam all the way down the middle of the model. I was wondering if anyone knew a better way of fixing this. Any help would be greatly appreciated. Thankyou.
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Old 24-02-2009, 02:43 PM   #2
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To solve it i guess only by remaping the entire piece and redo the whole texture.

Last edited by bluemana : 24-02-2009 at 02:51 PM.
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Old 28-02-2009, 08:06 PM   #3
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Default Unsolvable

Nevermind guys, aparently, there is NO easy way of adressing this problem due to the nature of Maya's UVs. Aparently games companies adress this by getting one of their engineers to create some extra code with maya's model exporter. Just thought I'd save anyone who runs into the same problem the bother of hunting for an answer.

In my previous post, I mentioned reversing the normal direction on the erroneous half of the model. While this works, it produced a distinct seam down the middle (maybe it was just the model, give it a try, might work fine for you). If however, like me, you get this seam, the most feasible solution with regards to saving texture space seems to be, to have overlapping UVs ONLY on geometry that come in pairs but don't actually connect or touch, i.e. gloves, boots, shouder pads, etc. On something like a cuirass/body armour/torso, it's probably easier to just map the whole thing as one uv set.

If you wanna know more, check out the following link. It gives a better explanation of the nature of the problem. Scroll down to "Flipped UVs Issue". It's a great Normal Mapping tutorial by the way.

http://www.bencloward.com/tutorials_normal_maps10.shtml
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Old 01-03-2009, 11:58 PM   #4
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Why don't you try to duplicate the material, assign it to half of the model, then you just change the bumpmap value to a negative one. I'm not sure if it would work.

In the Unreal Tournament 3 tutorials made by the guys from Epic, they show a way to solve this same problem. Something like not doing, the line where the seam would be, in the middle.
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Old 02-03-2009, 02:18 PM   #5
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Hey bluemana,

Yes that would work, I've tried it before, but does having more materials result in longer render times? Especially when you have 2 or 3 2048 textures? This is definitely another alternative to reversing the normals though.

What you said about the UT3 thing was interesting. Got a link by any chance?
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Old 02-03-2009, 08:34 PM   #6
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i dont think having more materials will increase render time.
after all, you haven't increased the amount of work that needs to be done since you are using the same texture just mirrored over. it's still going to go through the same calculations

about that definite line between your model... did you duplicate the half of the model, then do a negative scale, then do flip normals, then do merge verts along the border edges?
if you did then you missed out the softening of the centre edge that used to be the border edge. that may or may not be the problem. i would confirm it but this computer lacks maya...
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Old 03-03-2009, 09:06 PM   #7
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Hi Cherone,

Regarding that line/seam down the middle, The normals had been softened, indeed for the entire model. Still not sure what it was. I re-merged the vertices again but with a wider threshold and it seems to have solved it, so there's a chance it may have been some rogue vertices which had not been merged properly along with the rest.

That's great if the number of materials doesn't really affect render time. I completely forgot that as you said, I could just connect the same texture to multiple materials. I think this is probably the best way of tackling this issue in future.

Thanks alot to you and Bluemana for your help.

Here's a screenshot of my Model. Just needs to be textured.
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