)Many high-end graphics cards come with C source code for doing basic graphics
)sorts of things (change colors, draw points/lines/polygons/fills, etc.).  Does
)such a library exist for generic VGA graphics cards/chips, hopefully in the
)public domain?  This would be for the purpose of compiling under a non-DOS
)operating system running on a standard PC.

Check the server code for X11R5.  (or "XFree86")