Manually created UDIM images sometime don't get packed correctly

[colby3d]

When closing and reopening the file, painted layer information is lost, it looks like this happens when two different versions of the file exist, both versions of the image are lost if one is edited. This might be due to how the images are saved?

[ucupumar]

Can you record your process for reproducing the issue? It's difficult to figure out what's wrong there.

[colby3d]

sure, so what I did was save 2 versions of the file, edit the image in one, save, and open the other version. https://youtu.be/DXsMXizlcrs after which both versions of the file are missing the edited image.

[ucupumar]

Can you show the entire process? Like from the default cube scene, I want to know how did you create the layer image.

[colby3d]

sure, also I've figured out it's only when I use UDIMS https://youtu.be/IUPtiHiblEk
basically, just ucupaint setup > create layer> paint >save main file and alternate > paint on alt. > save > open main file > both files have lost the layer.

[ucupumar]

I see, I just tried just like what you did and yeah, it does not save on Blender 4.0, but it works fine on Blender 4.3. I'll check what's the problem there later.

[ucupumar]

I'm not sure what's wrong with Blender 4.0 but this issue only happens on that version (even Blender 3.3 is fine). If you manually fill the tile using the image editor, the image just won't get packed correctly. I found no way to detect if the image is manually filled using the image editor or automated using ucupaint.
To get around this issue you can refill the images using ucupaint's own operator, it will fill the images based on your current UV

And make sure not to fill the tile manually using the image editor.

[colby3d]

Issue happens in 4.3.2 as well, without filling UDIMS, the affected layers are alpha backrounds. I've also avoided saving alternate versions, this happens seemingly at random upon loading the file. Creating entirely new layers will also break the shader and turn the model pink at times, this might be related?

[ucupumar]

Can you record your process of recreating the issue again on Blender 4.3?

[colby3d]

sure, though it's not really a process, it's the same as with the other version but without backups/filling, just starting blender and layers made previously are gone (halfway through the video I notice a layer not broken but missing) the images look like they have some information but exporting and loading them as an image node shows they're missing most data, on the left you can see some strokes were preserved (the last ones on the layer). I've also noticed that creating new layers past a certain point seems to break the material in a similar way, could it be there's a limit to the number of images and new images break old ones after reloading? https://youtu.be/mRLGXPg1zE8

Edit: the blend file was also originally made in the previous version with the bug, and while it's a little different now, maybe that's part of the problem?

[ucupumar]

It's possible. Can you please try to recreate the issue directly in Blender 4.3 from the start?

[ucupumar]

I just made a fix to ensure manually created/filled UDIM images will be packed correctly when you save the blend file.

Also, I just checked your video again and the pink material is likely not related to this issue. It's probably because you hit the maximum UDIM image limit per material. I already compiled some info about that here https://ucupumar.github.io/ucupaint-wiki/01.11.extras/

The workaround is to convert all your UDIM images to use image atlas, the demo can be seen here https://x.com/ucupumar/status/1716421635513987331

[colby3d]

yup, you're right that was the issue with the new layers, converting to atlas fixed that, thanks!