Graphical Window Sprites
version 1 by Erik Temple
Section: Producing Images for Use with Graphical Window Sprites
Full instructions for producing images are well beyond the scope of this documentation, but a few notes and links will be useful. For almost all purposes, you will want to produce your images in PNG (Portable Networks Graphics) format. PNG graphics (file extension .png) can contain an "alpha channel" that defines transparent areas of the image, allowing for shapes that are not rectangular. They can be produced with Photoshop, of course, but also with many other programs, including the free, cross-platform GIMP software (http://www.gimp.org). Here are some sites that might be of use to you if you are unfamiliar with PNG graphics (Inform tends to mangle URL spacing, so you may need to edit them by hand):
http://www.axialis.com/tutorials/tutorial-misc001.html (Photoshop tutorial)
http://www.fabiovisentin.com/tutorial/GIMP_transparent_image/gimp_how_to_make_transparent_image.asp (GIMP tutorial)
When sprites are intended to fit together tightly on screen, as for example image tiles, we will have more flexibility if we design the tiles so that they overlap one another. In other words, where they will abut one another, we should include an extra margin of 1-3 pixels in each image. This will ensure that, if the sprites are scaled, the inaccuracies inherent in scaling do not create visible seams between sprites.