Undo incorrectly frees all the ImBufs of tiled images #97015
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Reference: blender/blender#97015
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Delete Branch "%!s(<nil>)"
Deleting a branch is permanent. Although the deleted branch may continue to exist for a short time before it actually gets removed, it CANNOT be undone in most cases. Continue?
System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Blender Version
Broken: branch: master from August 20th 2021
962153dbed
Worked: branch: master from August 19th 2021
a217e043be
Partially caused by:
0896457c59
with the following line in particular:ima->cache = NULL;
Removing that line allows 1-level of undo/redo to work correctly, but not multiple...
Short description of error
Undoing the addition of new image tiles for tiled images actually frees all ImBufs associated with the image.
Exact steps for others to reproduce the error
Here's is what things look like after you create an Image, add 2 more tiles, and then add another 2 tiles:
Here's what it looks like after Undoing just once from that state:
Added subscriber: @deadpin
Changed status from 'Needs Triage' to: 'Confirmed'
Added subscribers: @Sergey, @Jeroen-Bakker, @brecht, @mont29
From quick reading of code, it looks like content for tiles is only stored in the (supposedly runtime-only)
Image.cache
(BKE_image_fill_tile()
...). So this issue does not only affect undo/redo, but also file save/reload, since this cache is never written nor read.Am not sure what is going on here tbh, to me this looks like a giant mistake in code, but... maybe @Jeroen-Bakker, @brecht or @Sergey know better about this?
@mont29, this pointer is supposed to be restored through the
BLOCacheStorage
mechanism, but that's failing here.It appears that
BKE_idtype_cache_key_hash
andBKE_idtype_cache_key_cmp
take into account the cache value (ima->cache
), which becomesNULL
here. Using the cache value seems wrong for these functions, it's somewhat surprising this worked at all?@brecht this looks wrong indeed - although I guess it was working OK-ish before we started null-ifying runtime pointers on write...
But I don't think fixing this would fix the actual issue with generated image tiles. With regular generated image, its type is stored as part of the data, and can therefore be re-generated when the cached ImBuf is lost. With UDIM tiles, there is no data stored at all about them being generated image, so generated content is lost once cache is lost (on Undo currently, but also on file save/load e.g.). This sounds like a fairly weird design if that's the intended behavior...
And with that current design, fixing the broken cache handling on undo won't fix the issue on redo's, since the ImBuf's of the later-added tiles will be removed from the cache when undoing, they won't be available again on redo, leading to the exact same empty tiles issue again. Same problem if you try undoing tiles removal, and so on.
Regarding handling of caches across undo/redo: Think it makes no sense to use the cache pointer value in the key anymore indeed. Also found that current code (storing the cache value in the key, and then trying to use that as actual data value) is extremely bad design... Not proud of myself for having done that two years ago :(
See D14559 for a proposed fix for the cache handling issue itself. As already stated, this does not address all the issues at play here, by far.
The generated image parameters should really be stored per
ImageTile
. Looking through theImage
struct, I don't see anything else that belongs there, all the other stuff seems like it should be shared.This issue was referenced by
e06399c223
Changed status from 'Confirmed' to: 'Resolved'
Created #97251 (Generated UDIM tiles do not store any info about their parameter) for the missing data storage in UDIM tiles, think this report itself can be closed now.