These demos run only on SGI machines and require the 'gl' built-in module.
The demonstrate the abilities of SGI's GL library as well as the ease of
GL programming in Python.  Most demos require the Z-buffer (aka
24-bitplane) option.

backface       Demonstrates the 'backface' GL function.

kites          Show 3 flying kites.  Demonstrates the rendering speed
               obtainable by Python programs.

mclock         A colorful clock with more options than you can
               remember.  Works on 8-bit machines (but allows more
               colors on 24-bit machines).

mixing         Demonstrates the effect of color mixing: through
               frequent color switching it gives the effect of white
               light.

nurbs          A simple demonstration of the 'nurbs' GL functions.

zrgb           Displays a 3-D Gouraud-shaded figure which can be moved
               around with the mouse.
