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Optimize KoClipMaskPainter with XSimd for the final compositing.

Wolthera van Hövell requested to merge woltherav/krita:text-tool-phase-1-optimize-drawing into master

A few months back @dkazakov identified that there were two places the KoClipMaskPainter was slow: The initialization and the final compositing.

This replaces the slow function in the initialization with a set of QPainter calls, and implements xsimd functionality for the final compositing, following the code in KoStreamedMath. This is the first time I've done anything xsimd related, so I might be doing some awfull stuff there.

I have not done any profiling on this, but it feels a lot faster. However, it doesn't prevent the little delay that sometimes happens when typing text inside the text shape. This same delay also doesn't seem to be affected by minimizing the delay of updateCompressor in KoShapeManager_p.h, so it must be caused by something else (given that the cursor updates quite rapidly, it doesn't seem to be the text layout itself either). Similarly, when coverting a given text to a path, it is still a lot faster to move around, so it might be beneficial for text to not use KoClipMaskPainter at all when not painting with bitmap masks, and instead transform the painter or the background so that it can draw the gradient correctly.

Outside of those pipe-dreams, this does speed something up, so it is still a useful change.

Test Plan

Make a 300DPI canvas and add a 72 pt text. Move it around with the shape select tool.

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.

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