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Resolved UV Map channels. How do they work?

Discussion in 'Formats & External Tools' started by GerardChalaux, May 1, 2021.

  1. GerardChalaux

    GerardChalaux

    Joined:
    Sep 11, 2018
    Posts:
    17
    Hello everyone.

    I had an issue with the UV Map of a mesh I exported as .fbx from Blender; when I imported the mesh into Unity and created a material with its UV map it looked all wrong. Trying different things I figured the issue was the UV channel so I manage to solve it by checking the 'Swap UVs' on the Inspector in Unity on import.

    My question is: Why? I need help understanding why my UV was on the second channel and how did it happen.

    For more information the Blender file I exported the mesh from has another mesh with its own UV Map, which worked perfectly using UV0 (first channel); would that be the reason? If so what's the proper way to manage UV Maps in Blender when using a single file?

    I'd really appreciate it if someone could enlighten me about this. I attach a pic of what I'm talking about for context. On the bottom right corner you can see I created another UV Map for that second mesh.

    Thank you very much.

    UVMapIssue.jpg
     
  2. kburkhart84

    kburkhart84

    Joined:
    Apr 28, 2012
    Posts:
    910
    That is the literal reason why you have the issue. Each mesh has its own UV maps, so there is no issue if you delete or modify the first slot UV map of the mesh regardless of if it is in the same file.

    The main reason to have a second UV map is if you are using light mapping, and don't want to use the UVs that Unity generates for that purpose and prefer to generate the lightmapping UVs yourself.
     
  3. GerardChalaux

    GerardChalaux

    Joined:
    Sep 11, 2018
    Posts:
    17
    Ooooh I see. I misunderstood the whole thing. I'm still relatively new to Blender and some things are still confusing to me. For whatever reason I thought UV Maps (which I didn't know were channels) were shared between all meshes; now I see it's the Image that is associated with the mesh material.

    Thank you very much.
     
  4. kdgalla

    kdgalla

    Joined:
    Mar 15, 2013
    Posts:
    4,669
    You have two UV maps in your blender file for some reason. Unity only uses one. From my experience, the UV map on the top of the list in Blender goes to UV0. If it doesn't work, try reordering that list.

    Are you using the texture atlasing plugin in Blender by any chance?