I like the idea. Also, it would be supercool if you could use variables like
$h to refer to the width and height (e.g.
$w + 32 instead of
256 + 32). This would allow to easily create canvases with specific ratios (e.g. Golden Mean, rule of thirds, etc.).
This feature would require adding a formulas parsing engine, so it’s probably quite some work on Jan’s side.
PS: @cageburner, if you want Jan to see your proposal, to be on the safe side always mention him by including @jan.cosmigo in your post, so he get’s notified that it’s a post direct at him and the post doesn’t go by unnoticed (in case there is a flood of posts).