Bug 423226

SUMMARY
Input 'drawing angle' in brush engines (both pixel and color smudge) is getting affected by the mirror mode. All the other inputs are independent of canvas mirroring, only the drawing angle gets a 180 degree offset when in this mode.

Video (rotation -> drawing angle):
https://youtu.be/q4cEyipjCp8

STEPS TO REPRODUCE
1. Pick any non-symetric brushtip
2. Connect any output to drawing angle (best seen with rotaton)
3. Draw with and without mirror canvas mode (M) enabled 

OBSERVED RESULT
Brushes get 180 degree offset in mirror mode

EXPECTED RESULT
Mirror mode don't affect the brushes (relative to the user)

SOFTWARE/OS VERSIONS
Windows: Windows 10
macOS: -
Linux/KDE Plasma: Kubuntu 20.04
(available in About System)
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8

ADDITIONAL INFORMATION
Best seen with rotation -> drawing angle connection, when the tip is rotated 180 degree, but it seems to occur with all the other outputs (tested with size which switches from minimum to maximum on the left without mirror mode, and on the right with it)

Tested the issue both on Windows 10 and Kubuntu 20.04. I recreated it in krita 3.3, as that was the oldest appimage I could find fast.