Correct way to change UVs on imported fbx mesh via AssetImporter

I'm using

void OnPostprocessModel(GameObject gameObject)

to change the UVs of an imported fbx model's mesh at import time through the use of a custom AssetPostprocessor class.

This appears to be working so far: I reimport my model and the UVs are changed. I can close the editor, reopen, play and everything seems to be working correct.

However, I noticed that none of my files have actually changed on disk. I have my project checked into external version control (Mercurial) and neither the FBX nor any meta file actually show a change. Also, when opening the project on a different computer, the models don't have the changes. I have to manually reimport everything.

Is this intended behaviour? That I need to reimport all models on all machines again, or can I somehow store my UV changes made to the FBX mesh?

 

Well, I found the issue: By default, there is an option "Optimize Mesh Data" enabled in the Player Settings. The documentation states, that this removes any mesh data (uvs, tangents, colors), which is not used by a material on the model.

My problem is, that the materials/shaders using my custom UVs are instantiated at runtime and I didn't know about this optimization option being enabled by default. It took my quite some reading and experimenting until I found this very specific case. I still reported it as a bug, because I believe that stripping features should be disabled by default or somehow configurable. At least I should get some kind of report that stripping optimizations have been performed, so I that I notice the error.

The simplest fix was to disable the optimize mesh data option. Alternatively, it may work if I apply the material at edit time.

 

Hey! I was wondering how do you actually force FBX to be saved to disk inside void

OnPostprocessModel(GameObject gameObject)

?
I did disable Optimize Mesh Data but when forcing FBX reimport by deleting and pasting the file to the same folder, it doest launch all AssetProcessor sequence. Hovewer I don't see any changes in files in Git.
I read somewhere that you should call

assetImporter.SaveAndReimport();

in the end of OnPostprocessModel to save changes in FBX but this doesn't work either.