open-axiom repository from github
% operand stack configuration in order to use psDrawFilled:
% psFillwOL
% XPoint[0].y
% XPoint[0].x
% n
% ...
% XPoint[n].y
% XPoint[n].x
% graphics-context dictionary
% this draws lines connecting all the points and fills the
% region with background color (default: 1, or white).
/psFillwOutline
{ gsave
newpath
yVal moveto
1 sub {
yVal lineto
} repeat
closepath
begin installGC
gsave fill grestore %% fills with foreground color
0 setgray stroke grestore end } %% outline it with black
def