Mirrored UVs. Topic for discussion.

[Callak]

I have been trying to do something with my current model ( And my first complete model/avatar/character ) that seems smart, but I think may cause problems.   Left/Right mirroring of UVs.   Easy to accomplish in blender if you are building half a model, and just mirroring the other side.... assuming everything about the other side of the model is identical.   For live, web based end mediums like Second Life, which is what my first full creation is meant for to start off with, this is smart because Second Life is bandwidth sensitive.  Every texture is sent to others over the internet, unlike games where textures reside on your desktop and don't have to be downloaded.   The way I feel this is smart is you only have to make half the texture, and let it be mirrored by the UVs, this means more texture space for detail without adding more download to the model.  However, while I'm not sure of this, I fear this might be creating complications for 3DCoat.   It accepts the model with the mirrored UVs, and I've accomplished a lot of painting on it in 3DCoat, and it looks good in 3DCoat, even acts like I have symmetry turned on when I don't, which is what I would expect, but I have to wonder if the mirrored, overlapped UVs are sometimes causing problems with the tools, perhaps sometimes causing crashes.   I'd like to keep this technique if possible, because it seems like a good idea, but I don't know enough about normals to be sure it's going to turn out correctly in the end.   I have gotten some warnings from friends who seem to know what they are doing about this causing one side of the normal map to appear inside out in SL, but I have tried it on early upload tests to SL, and it seemed to look correct to me.

Edited July 24, 2021 by Callak

[Carlosan]

Better ask @Silas Merlin

As I remember he makes models for SL.

[Silas Merlin]

1 hour ago, Callak said:

, but I have tried it on early upload tests to SL, and it seemed to look correct to me.

If it looks correct in SL then that is all that matters, I think ?

As for the crashes, I don't know. Could it be something else ? Always save incrementally while you work, often. If you crash reopen the last one and do the same thing. If the crash occurs again then you could send the file to support because it means the crash can be reproduced.

Personally, when I work with overlapping uv's, I only export the diffuse.
in my tests, my issue was with visible seams at the symmetry line. At the time I did not think of a solution for that (making the normal map blank at the symmetry line).
but to be honest I never thought of the normal map facing the wrong way on the other side, which must happen for sure. Play with a light inworld on your model, and you will surely see that it is the case. (I mean, not from experience, but it ought to look strange)

The default avatar does have mirrored/overlapping uv's on the foot and arm. It works, but it doesn't have materials, only diffuse.

[Callak]

10 minutes ago, Silas Merlin said:

As for the crashes, I don't know. Could it be something else ? Always save incrementally while you work, often. If you crash reopen the last one and do the same thing. If the crash occurs again then you could send the file to support because it means the crash can be reproduced.

I'm mostly concerned about my odd technique, and that it might be causing more problems than the ordinary user, because I am looking at techniques that most people don't, for the purpose of efficiency on the final medium the work is intended for.    If this was a game, I wouldn't mind using the texture space, and just fully UVing my character.   But I'm looking for technical ways of conserving bandwidth for this because it's for Second Life.  My worry is that 3DCoat is not really designed for this sort of thing, and I might be causing some of the crash issues I have been experiencing for my unusual development methods.  That said, I'm also a noob, and I realize this is not usually how things are done.   But I can see the benefit of doing them this way for the purpose of mediums like Second Life.

Edited July 25, 2021 by Callak

[Silas Merlin]

I am pretty sure that stacking uv islands is quite common, don't worry.
also, generating such uv's is built into the retopo room in 3d-Coat.
(you need to unwrap before you apply symmetry, and the islands will be automatically mirrored and stacked. you can also do it manually island by island with the copy uv / paste uv tool)

Edited July 25, 2021 by Silas Merlin