Issue Summary

This is an issue related to the undo that I think it's quite critical and can occur a lot for most users. The problem that happens is that if you undo beyond a two step threshold, the frames content will be erased permanently. I've tried this by creating new frames and drawing over existing frame containers, but the result is the same.

Video or Image Reference

https://www.youtube.com/watch?v=mind6giVf_Y

Note: From 0:32 to 1:16 I mention a UX issue with the undo shortcut that has been in the software for a long time and it drives me crazy. I'll report that separately.

Expected Results

Invoking the redo function should accurately recover the strokes or drawings that were "erased" after invoking the Undo function, otherwise we can't trust this functionality when it comes to gauging variations in the work, or worse when we thought we might have been wrong, but decided to keep going, after we redo the work everything else is lost.

Steps to reproduce

1. Create at least 5 frames to see the effects of the issue
2. Draw on each separate frame a single stroke
3. Undo all frames to notice the effect
4. Redo the last 5 frames you undid. Notice you'll only get back the last action / frame worth of content

System Information

• Pencil2D Version:
  Nightly Build Nov 14 2021

commit: 91b1721
date: 2021-11-14_16:46:59

Operating System: Windows 10 Version 2009
CPU Architecture: x86_64
Qt Version: 5.15.2