links to software relative to polygons (clipping and and other operations)

used in freePCB (Written by Alan Wright)
gpc (here: GenericPolygonClipperLibrary.cpp)
http://www.cs.man.ac.uk/~toby/alan/software/gpc.html

polygon.php (ported in "C++" by Alan Wright)
the c++ corresponding file is php_polygon.cpp
http://www.phpclasses.org/browse/file/10683.html

used in gpcb:
polygon1.c:
http://www.koders.com/c/
and for this file:
http://www.koders.com/c/fidE26CF2236C2DF7E435D597390A05B982EDFB4C38.aspx

gpcb uses a modified file (integer coordinates)
