We can now select a LED on the screen and get the index of the LED.
To get the right index, we use the color picking technique mentioned
in the OpenGL RedBook. This works suprisingly pretty well (and fast!).
The idea is to use OpenGL and some simple C code to display a 3D cube.
With the mouse you can define which LED should be on or off on a
particular frame. With this technique, you can define whole sequences of
frames to form animations.
