Documentation is like sex: when it is good, it is
very very good; and when it is bad its better than
nothing. - Dick Brandon

Concept 3.4 : Orthographic Projection
=====================================

Idea
====
glOrtho()  is the function call to specify orthographic
projection.  With an orthographic projection the
viewing volume is a rectangle parallelepiped. No 
foreshortening occurs.

glOrtho(left, right, bottom, top, near, far);
( left, bottom, -near ) and ( right, top, -near ) are 
points on the near clipping plane that are mapped
to the lower-left and upper-right corners of the 
viewport window respectively.  ( left, bottom -far )
and ( right, top -far ) are points on the far clipping
plane that are mapped to the same respective corners of 
the viewport.  Both near and far can be positive or
negative.

Experiment
==========
As in the case of perspective projection try different 
values for the various parameters and see how the viewing 
volume affects the final rendered image.