[3ds Max] Can I Flip UV's without Inverting Normals?

Dubious_Fellow

Hi, I have two identical objects facing each other. Can I flip the UV's of one and stack on top of the other without it inverting its normals?:

-thanks!

Noren

The normals of the UVs will be inverted. The mesh normals usually won't. If normal and bump maps are displayed correctly depends on the renderer or real time engine used.

Dubious_Fellow

Noren said:

...depends on the renderer or real time engine used.

Its going into UE4.

EDIT: *Throws down Rare Candy in the hope of attracting a wild Chad*

Noren

Never used Unreal, but I don't see why it shouldn't be able to deal with mirrored UVs. Are you having any problems?

Dubious_Fellow

Noren said:

Never used Unreal, but I don't see why it shouldn't be able to deal with mirrored UVs. Are you having any problems?

I am still a little confused. If I understand correctly, you can't "flip and stack" because the tangents would be reversed on the flipped UV's: concave normal details would become convex and vice-versa (regardless of engine)?

-So the answer is 'no'?

EDIT: I'll be using Painter to create the normal map.

Mark Dygert

I think it is still a problem with only certain pieces of software not exporting the tangents and binormals correctly. I don't bake in 3dsmax any more, I use substance and I haven't run into in a while, but then again I don't mirror UV's as much as I used to. Personally I wouldn't use 3dsmax to bake anything, RTT is broken and bugged so bad it's unusable, plus it doesn't output half of the maps that I actually need.

Noren

"concave normal details would become convex and vice-versa (regardless of engine)? "

In theory, yes. But since that's easily fixed by identifying the flipped UVs and inverting the normals in engine that usually isn't a problem anymore. To be safe, you should just bake the unflipped, unstacked normals though, so move the other UVs one tile over or delete them while baking. And using an aligned renderer and engine like Mark suggested is definitely a good idea.

poopipe

It works fine in ue4 

gvii

If it's for a normal map bake, I usually flip the UV's to match, stack em, then keep properly oriented shells in the 0,1 space and offset the rest.

poopipe

That is the correct way to do it.  You risk subtle artefacts at seams if you bake to the flipped shells