Just a heads up, the viewport scrolls in Firefox on Android while you're painting. Everything still works otherwise, but it makes it hard to draw because the canvas is moving with your finger. I'm guessing it has something to do with the URL bar changing the viewport height because the extra space seems to be roughly the same vertical height.
Awesome work by the way, it's a lot of fun to play with.
Awesome work by the way, it's a lot of fun to play with.