This tutorial demonstrates how to use offscreen rendering and
dump an image or a mpeg movie.
Rotating cube by C. Benoit.
CPlot can render in an image file or in a mpeg movie file.
If you are using CPlot on a cluster (with no graphic card),
it must be installed with mesa. Then, when using
offscreen is triggered with offscreen=1.
If you are using CPlot on a computer with a graphic card,
you must use offscreen=2.
In this tutorial, we consider a Cartesian grid, make it rotate
and dump image to a file at each step.
The movie must be finalized at the end. A wait time is added before
finalizing to be sure that render is finished.