Here's a third tutorial from Guus focused on GPU-assisted plotting. It also provides excellent exercices on manipulating the OpenGL windows using the Viewport and the Scissors

http://en.wikibooks.org/wiki/OpenGL_Programming/Scientific_OpenGL_Tutorial_03

The OpenGL wikibook is free documentation, and you are welcome to redistribute it under certain conditions; see the CC-BY-SA or GFDL licenses for details