Just having a flick through paint and paintutils, and a couple of things we could definitely improve:

paintutils

• Redundant type checks: https://github.com/SquidDev-CC/CC-Tweaked/blob/6734af6e4a7ec411e447e0b4fb6066101eb2da8a/src/main/resources/data/computercraft/lua/rom/apis/paintutils.lua#L74-L76

• Box drawing should use term.blit. We should still probably keep the term.setBackgroundColour for "backwards compatibility".

• Experiment with using term.blit for drawing images. Sadly images are stored using tables of numbers, so we can't blit super efficiently, but worth seeing if it's any faster anyway.

  It occurs to me that this won't work with transparent images, so may not be possible at all.

paint

• Drawing the initial image is slow. We should replace drawCanvas with a term.blit based version and see if it is any faster.

Happy to take a stab at the blit stuff, if you haven't started already!

Made the paint improvements in aab0cd3. My goodness, it's absurd how much faster it is.