canoncialize the selection so start <= end

canoncialize the selection so start <= end

create the png data from post-deflated data

this function is designed to support animated gifs, although stb_image doesn't support it two back is the image from two frames ago, used for a very s

decode one 64-entry block--

get some unsigned bits

set up the kernels

read 16bit value and convert to 24bit RGB

Each scan line uses the same kernel values so we should calculate the kernel values once and then we can use them for every scan line.

What output pixels does this input pixel contribute to?

What input pixels contribute to this output pixel?

find minimum y position if it starts at x1

find minimum y position if it starts at x1

compute the result of dragging away from a tile

because detecting that undo is available

returns -1 if value changes, 1 at end of drag