SUMMARY Pixel lines are not correctly mirrored with half-pixel aligned mirroring tool. STEPS TO REPRODUCE 1. Create an odd-sized small image (ex: 7x7) 2. Select a pixel drawing brush 3. Zoom in and place the cursor on the left side of the mirroring tool 4. Click on the left half of a pixel OBSERVED RESULT Only the pixel under the cursor is painted. EXPECTED RESULT Another pixel should have appeared, mirrored on the right side. SOFTWARE/OS VERSIONS Linux: Gentoo Krita: AppImage 5.2.9 (git ac6cae8) ADDITIONAL INFORMATION Also, the line tool is broken. I suspect there is some shenanigans regarding rounding up or rounding down when converting the mouse position (which is sub-pixel aligned), into the pixel index to actually paint, but can't be sure.
Forgot to mention a step between 1 and 2: "Activate the vertical mirroring tool".
Reproduced and confirmed this on Windows 10. I have included a video that also confirms which part of a subpixel you paint is important. As seen in the video, if your brush size is more than 1px (in this case 1.5px), you can paint 2 pixels at a time, but only the one that is "touched" by the cursor on its right half will get mirrored. One correction to the initial description: the canvas resolution doesnt matter, it depends on here you place the mirror. This bug only happens if the mirror is placed in the center of a subpixel, similar to this bug: https://bugs.kde.org/show_bug.cgi?id=502855 Possibly some could have something to do with the subpixel coordinates with a subpixel-mirror. I will try to test this further in the coming week.
Created attachment 181339 [details] Showing that a larger brush size can only mirror right halves of pixels.