The xgd library is a modified version of the gd library by Thomas Boutell,
the changes are...

incorporation of allegro polygon filling code to fix the banding problem.
incorporation of multiple clipping regions to make a binding to the libwmf
project possible.
incorporation of the freetype font support of gdtcl by John Ellson
addition of xpm handling to make it easier to handle dibs for libwmf.
added ability to load xbm's from data.

the original readme is 
readme.original, gd1.3 from http://www.boutell.com/gd.
polygonworking.c, is from allegro, and contains its licence agreement.
gdttf.c, is from Gdtclft1.9.6, http://www.tcltk.com/ftp/ellson/

Caolan.McNamara@ul.ie
http://www.csn.ul.ie/~caolan/docs/libwmf.html
