Nonconvex polygons or simple polygons containing holes,
must first be subdivided into convex polygons before they can be displayed.
All polygons can be formed from unions of simple convex polygons.
The simplest convex polygon is a triangle, since any three points always lie on a plane.
A subdivision that breaks polygons down into groups of the simpler polygons
that can then be rendered
is called tessellation.
A subdivision into triangles is called triangulation.
GLU provides a collection of routines that perform tessellation and triangulation.
-> Splitting concave polygons,
-> Triangulation (tranformation in set of triangles).