to be is to do. -- I. Kant
To do is to be. -- A. Sartre
Yabba-Dabba-Doo! -- F. Flinstone

Concept 2.2: Polygons
======================

Idea:
=====
Polygons are the areas enclosed by single
closed loops of line segments, where the line 
segments are specified by the vertices at
their endpoints.

In general polygons can be complicated, so OpenGL 
makes some strong restrictions on what constitutes a 
primitive polygon.  

	o  The edges of a polygon may not intersect
	   i.e. has to be a simple polygon.
	o  OpenGL polygons must be convex, meaning that
	   they cannot have indentations.

Convexity: 
==========
A region is convex, if given any two points in the 
interior, the line segment joining them is also in
the interior.  The program to your left shows some valid 
and invalid polygons.  

Many real-world surfaces consist of nonsimple polygons
nonconvex polygons or polygons with holes.  All
such polygons can be formed from unions of simple
convex polygons.