Those who can, do.  Those who can't, simulate

Concept 1.1 : Clearing The Window
==================================

Idea:
=====
We took a brief look at changing the background
color while learning Concept1.4.  We try to 
understand the theory here.
 
On a computer, the memory holding the picture
is usually filled with the last picture you
drew, so typically one need's to clear it to
some background color before one start's to
draw the new scene.  

As an example, these lines of code clear an RGBA
mode window to black:

glClearColor(0.0, 0.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);

The first line sets the clearing color to
black, and the next command clears the entire
window to the current clearing color.  The single
parameter to glClear() indicates which buffers are
to be cleared.  In this case, the program clears only
the color buffer, where the image displayed on the
screen is kept.  

Typically you set the clearing color once, early in
your application.  At this point, it would not be
a bad idea to review some of the examples in Chapter1
to see how the above lines of code are positioned
with regards to the overall structure of the program.

Also other buffers might be encountered in your 
experience.  Some other buffers are the depth buffer
specified as GL_DEPTH_BUFFER_BIT.  Listed below are
common buffers :

====================================================
Buffer           Name  
====================================================
Color		 GL_COLOR_BUFFER_BIT
Depth		 GL_DEPTH_BUFFER_BIT
Accumulation	 GL_ACCUM_BUFFER_BIT
Stencil		 GL_STENCIL_BUFFER_BIT
-----------------------------------------------------

Before issuing a command to clear multiple buffers, you 
have to set the values to which each buffer is to be cleared.  
Further you can clear multiple buffers by logically "OR'ing"
them in the glClear() command:
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);