I'm wondering how you actually create an imageset. Painting in the Gimp, exporting and then manually setting all the coords and sizes seemed to complicated (*). Therefore I wrote a little Script-Fu Script for the Gimp to help me with the creation of imagesets.
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This script uses the layer information (name, pos, size) to create the images in the .imageset. Offsets must be inserted manually later.
(*) Actually learning the SCHEME language and putting the script together in a lenghty trial-and-error-process wasn't that easy either.....
This script should run on any gimp 2.x installation (no perl or python required).
Please have a look and give me your feedback!
http://registry.gimp.org/node/6128