Getting pixels back out of a pixmap (getting them in is easy!)

[Steve Baker <ssbaker primenet com>]

Help! Once I've drawn on a pixmap, how can I get access to the pixels
in memory? I'd like to be able to find out whether individual pixels
are on or off. How can I do this?

Steve Baker <ssbaker@primenet.com> | kiku wa ittoki no haji
            <stbak@aol.com>        | kikanu wa matsudai no haji