Interesting tool. Thank you for sharing!!
If you try to change the Canvas Size and leave one of the spaces blank and hit 'Enter', it crashes and you lose everything:
ERROR in
action number 1
of Draw Event
for object Window:
to_real: blank string.
Just make it toss up a nag message in the event of a blank field?
Also freeze crashes if you give it really huge numbers. Implement a max cap?
Go to Edit > BG Color and simply press cancel, it selects red for your BG, even though you did nothing.
The blinky stamp marque selection box isn't visible enough on darker backgrounds. I suggest less transparency and a 32fps blink. Also make the box alternate between white and black when it blinks or change the selection box from a solid color to a dotted black/white line, like most image editing apps.
A large canvas, especially with large tiles becomes really clumsy because the testmap in the top-right covers everything.