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View Full Version : Inverted UV=Inverted bump?

GrafOrlok
10-30-2002, 01:48 PM
I've noticed when you use the same UV for a mirrored piece, such as opposite side of a head, (ie just UV mapping half the head and mirroring geometry, freezing and checking normals) you end up with an inverted bump map on the mirrored piece. The bump goes inward intstead of outward. I see the logic in this because the UV on the opposite part is sort of inverted, so the UV gets a negative value.

But when doing this is MAX, the bump is OK on both sides. The reason must be that MAX uses UV's and bumps differently than Maya. But does anyone know an easy way of getting around this?

I do workarounds by assigning new materials to the flip side connecting the color and spec from the original blinn and creating a new bump-node with a negative value. This works, but it takes time and clogs up my hyper shade window... ;) Flipping the normals outside in also works, but this is a bad option as you might guess.

Anyone?
GrafOrlok
11-01-2002, 08:37 AM
Come on guys! Somebody must have experienced this kind of problem. Don't be shy!
Crode
11-01-2002, 09:26 AM
what you described is what i did, ive seen worse clogged up stuff in hypershade

Im assuming that you took UVs from half a head and flipped them to overlap the others? Thats the problem right there is the flipping. I think if you scale the UVs -1 this doent happen but i havnt tested it too extensively.
GrafOrlok
11-04-2002, 08:18 AM
OK, I'll test it. Doesn't sound too convincing though, they should be scaled -1 just by scaling geometry negative...
playmesumch00ns
11-04-2002, 09:14 AM
Personally I normally wait until I've got the whole head model finished before I do the UVs. However, I think the UVs should stay the same, since the geometry is only scaled by the transform node, the shape node (and all upstream of it, including the UV nodes) should remain the same.

Can't understand why Maya would do that. The only thing I can suggest to fix it is to mirror the goemetry, then freeze transforms and delete history on the mirrored piece, then use transfer polygons to copy the UV data over from the original to the mirrored piece.

If Maya won't do the transfer then try using one of the many scripts available for this sort of task on Highend.

thinking about it, what you described may happen because Maya's creating two UV sets for the combined object, one for the original half's UVs and one for the mirrored half's UVs. This will create problems because until Maya 4.5 (well, I've been told they fixed it in 4.5), Maya would only use the first UV set it found for the bump channel and ignore any others you had. Very, very annoying!

Check in the relationship editor to see how many UV sets you got, if it's more than one, copying the Uvs into one set and deleting all the others should fix the problem.

good luck!
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