[Crespyl]

Depends on how feature complete you want it to be.

Back when I was working in Processing a lot, I could probably have whipped up something decent in an easy weekend. If I wanted to have more complicated features like flood fill, cutting/moving regions etc, I might need an extra day to figure it out.

If all you want is a bare minimum scribbling lines in a limited palette, that could probably be done in a matter of minutes.