I often use Image: Canvas Size to add a margin.
Recently mainly with mockups, where I want 12 px all around.
Doing the calculations in my head isn't too difficult, but does
eat time and makes me context switch.
One solution would be allowing calculations in the entrie: 436+24 ...
Typing +24 can be faster than erasing and typing 460.
*2 is faster than switching to percent and 200.
But that should be added on a GTK / per widget level, perhaps?
Another solution would be having fields for the margins or differences.
Would complicate the dialog, but could offer nice possibilities if
one needs different margins left/right/top/bottom.
Thorwil's Design for Free Software:
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