Bug 509739

SUMMARY
While drawing with Mouse Mark a rectangle (presumably a smoothing effect for the drawn lines) gets anchored to the cursor and it increases in size the further the cursor gets from the screens topleft 0,0.

For example on an 1920x1080 screen, if the cursor is drawing say at 0,540 the (anchored) smoothing box is now the size of 0,540 ie. it now touches the edge of the screen.

So I presume the origo of the smoothing effect for Mouse Mark lines is being drawn to the mouse position (as a rectangle?) instead on top of the of the whole screen.

STEPS TO REPRODUCE
1. Draw a lot of lines
2. Draw more on top of other lines and you'll see a shadow rectangle anchored under the mouse
3. Observe the shadow smoothing the drawn lines.

OBSERVED RESULT
The rectangle flickers the screen as it smoothes/unsmoothes the lines.

EXPECTED RESULT
No flicker and the lines are smoothed properly.

SOFTWARE/OS VERSIONS
kinfo:
Operating System: Manjaro Linux
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2
Kernel Version: 6.16.8-1-MANJARO (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 5800X3D 8-Core Processor
Memory: 128 GiB of RAM (125.4 GiB usable)
Graphics Processor: AMD Radeon RX 7900 XTX

ADDITIONAL INFORMATION

In the attachment the rectangle is very faint, it's a lot more noticeable on my monitor/with my eyes (I'm not sure why).

Possibly related bugs:
https://bugs.kde.org/show_bug.cgi?id=337044
https://bugs.kde.org/show_bug.cgi?id=501215