nice start!

i found out making my own cart that bitmap operations are a LOT faster if you use the pico-8 sprite space instead of your own lua data structure. because of how simple paintr is so far, the only thing that's really affected is clearing the screen, but if you want to add more complex features later, such as flood fill or layers, then you might appreciate the speed boost.

[edited for clarity and examples of features that benefit from a speed boost]