Bug 456134

SUMMARY
The 'fix' of https://bugs.kde.org/show_bug.cgi?id=455349 has bad consequences for some types of work with animated transform masks. It makes resizing very slow.
This fix is:
https://invent.kde.org/graphics/krita/commit/ea817fb6418c4866712ac88288113f8b6d2d3b3e

These consequences will be demonstrated in this Wishlist bug report by use of a demonstration file that can be downloaded from:
https://www.dropbox.com/s/brar1d1vx7in4li/Reveal-Generator-Demo.kra?dl=1 (19MB download).

The resizing of the transform masks should be an on/off option selectable by the user.
Personally, I'd be happy with a flag value in kritarc but a GUI Settings option may be preferred by some.

STEPS TO REPRODUCE
1. Download the Reveal-Generator-Demo.kra file (Dropbox link above).
2. Use version 5.0.6 to open it (before the change was made).
3. Play the animation just to see it.
4. Turn off the visibility of the 'Horizontal Thin Wedge R>L' animated transform mask - this is colour coded as blue.
5. Note that there are many different animated transform masks, any one of which can be selected (made visible) to create different animated effects, depending of which one of a few shapes from the 'All Shapes' group is selected (made visible). Please don't try that unless/until you're fully familiar with the file.
6. Do Image -> Resize Canvas to a new size of 5,760 x 4,320 pixels.
7. Note that this reveals a lot of previously off-canvas content. Imagine yourself editing this content or creating new off-canvas content.
8. Do Image -> Resize Canvas to the original size of 1920 x 1080 pixels.
9. Turn on the visibility of the 'Horizontal Thin Wedge R>L' animated transform mask - i.e back to normal use.
10. Play the animation and note that all is back to normal.
11. Quit with no saving.

12. Use version 5.1.0-beta1 or a later prealpha version to open it (after the change was made).
13. Repeat Steps 3. to 5.
14. Repeat step 6.

OBSERVED RESULT
6. This happens in a short time and reveals the previously off-canvas content.

14. See how long you are prepared to wait until the Resize operation is complete. I lasted for 3 minutes until I gave up and killed the appimage.

EXPECTED RESULT
An option to disable resizing of transform masks would be essential to work with this and similar .kra files.

SOFTWARE/OS VERSIONS
Appimages using Debian 10 MATE on an old desktop PC.