>># 
>># Copyright 1990, 1991 by the Massachusetts Institute of Technology and
>># UniSoft Group Limited.
>># 
>># Permission to use, copy, modify, distribute, and sell this software and
>># its documentation for any purpose is hereby granted without fee,
>># provided that the above copyright notice appear in all copies and that
>># both that copyright notice and this permission notice appear in
>># supporting documentation, and that the names of MIT and UniSoft not be
>># used in advertising or publicity pertaining to distribution of the
>># software without specific, written prior permission.  MIT and UniSoft
>># make no representations about the suitability of this software for any
>># purpose.  It is provided "as is" without express or implied warranty.
>># 
>># $XConsortium: plygnrgn.m,v 1.5 92/06/11 17:37:59 rws Exp $
>># 
>>#
>>TITLE XPolygonRegion CH10
>>ASSERTION A XPolygonRegion-1
A call to XPolygonRegion returns a region comprising the
interior of the filled polygon as described by the n points
specified by the points argument, filled with the fill_rule
argument.
>>STRATEGY
For a convex, concave and complex polygon :
   For fill_rule = EvenOddRule, WindingRule :
      Create a polygon region using XPolygonRegion.
      Create a gc using XCreateGC.
      Set the foreground of the GC to W_FG ^ W_BG.
      Create a drawable with background W_BG using XCreateWindow.
      Fill the polygon on the drawable using XFillPolygon.
      Set the GC clipmask to the region using XSetRegion.
      Set the graphics function of the GC to GXxor using XSetFunction.
      Fill the drawable using XFillRectangle.
      Verify that the entire drawable is W_BG.
