Unity 6: reordered vertices

Mesh from 2020.3.48 - optimize mesh - nothing;
Open project in Unity 6 (6.0.27f1) - reordered some vertices on UV seams (vertices number after 14K).

This is headache - breaks project functionality.

Optimize mesh - disabled.
Why reordered?

Hey ILonion,

Apologies for the delay; would it be able to get some more info about the settings before, after, perhaps some screenshots?

And if you feel like there’s a bug, please do feel free to report a bug and our engineering group will look into it!

Hi George,

Unity 2020.3.48f1:

  • there are 2 meshes: 1 called body, 2 - clothes;
  • both has same vertices positions and topology, different UV islands;
  • each clothes vertex index stored in List<> array with correspond body vertex index;
  • each clothes vertex index follows position of body vertex with positive offset by body normals (a-la clothes on body);
  • List<> array created once and serialized;
    Works perfectly well.

copy project via explorer;
open in U6 with reimport…

Unity 6000.0.27f1:

  • all the same;
  • some of clothes vertices wrong (see video), because correspond body vertices replaced its indexes;
  • seems like this situation happened on body UV seams only, randomly places (not whole UV seam)

How to make bug request? I can’t send whole project to engineering group - too complex project: Smile Girls 2025

I had same issue multiple times in upgrading path from 2021 to 2022 to 2023 and later. this is quite annoying and seems to happen only with bigger meshes. I also noticed that vertex order and / or number of vertices differ if you import on AMD CPU vs Intel CPU, which is even more annoying.
AFAIR I did send in a test mesh to some of your colleague a while ago.

It’s in Help - Report a Bug.
You can remove the project folder and only add the required files, or make a small repro project (way easier to reproduce and fix)

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AFAIR I did send in a test mesh to some of your colleague a while ago.

Do you have a bug #? and I can dig it out.

And yes! + to DevDunks instructions for filing a bug!

ah, sorry, had a look, this was the thread back then, but I never reported the bug because I got annoyed that no bugs get fixed. As it’s still the same or worse than back then (now bugs get closed although they are legit bugs), I see no reason to invest as much time in reporting than I did before.

Hey Qleenie,

Apologies that you had that experience. I’ll admit that as a developer bug-fixing can be a bit of a balancing act (and sometimes we don’t get that right!).

Take the issue in this thread, as an interesting example:

  • The Unity application relies upon the FBX SDK for 3D file imports. The issue may be traced back to the Unity codebase, but based upon the description I wouldn’t be shocked if it was caused by one of our SDK updates, which makes a fix much more complex involving multiple parties. We have automated tooling to catch as many of these scenarios as possible, but given the amount of variety in 3D models it’s understandably quite difficult to catch every scenario.

  • If we track the issue to the Unity codebase, we may be faced with a challenge (which we often have with asset importers!). If we restore the vertex-layout of 2023, then we may inadvertently break projects which are already on Unity 6. In cases like that, we sometimes solve it by adding an option to the importer to allow users to keep the old functionality, but then we get into issues where the Model Importer is increasingly challenging to use due to the number of import settings.

That’s all to say, if you file a bug, I can’t promise that it will be fixed. But everyone on my team really cares about both Unity (and this importer specifically…!). So what I can promise you is we’ll take a serious look into the issue and see if there’s anything we can do to either fix or mitigate it.

thanks, next time I’ll encounter it, I’ll submit a report. But will be more rare now, as I started storing mesh data into scriptable objects for that reason.
What should be easy to test though is the difference AMD vs Intel CPU on import, which is quite interesting. I have meshes which have different poly count on AMD and CPU PCs, and I tested with 4 different PCs (2 AMD and 2 Intel).