Make pixel smoothing work and not sabotage dynamics

Carsten Hartenfelsrequested to merge
hartenfels/krita:feature/pixelperfect into master

Pixel smoothing is supposed to make single-pixel lines not double up. It didn't actually do that, now it does.

It also no longer annihilates all other paint information than positions, artists who want to use pixel lines can have dynamics now (although most don't work because Pixel smoothing requires sharpness to be cranked up to the max to actually work and that in turn obliterates opacity dynamics) and this removes another source of "why is my pressure not working" (I got tricked by this because I didn't expect the smoothing of all things to destroy my pressure response.)

Here's a comparison, wrong pixels blink red.

Before/after comparison

Test Plan

  • Pick a 1 pixel brush with sharpness all the way up, enable Pixel smoothing in the freehand tool.
  • Draw a wavy line or something. Observe that it the line is 1 pixel thick, without doubled-up pixels or jags.
  • Pick a brush with dynamics, keep Pixel smoothing enabled. Draw something. Observe that the dynamics apply instead of everything being at full blast.

Formalities Checklist

  • I confirmed this builds.
  • I confirmed Krita ran and the relevant functions work.
  • I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
  • I made sure my commits build individually and have good descriptions as per KDE guidelines.
  • I made sure my code conforms to the standards set in the HACKING file.
  • I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.
  • Does the patch add a user-visible feature? If yes, is there a documentation MR ready for it at Krita Documentation Repository?

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