It is very easy to produce parametrizable figures with MetaPost. Merging a list of figures can make some animation, but this last task may be done by other programs (
convert [ImageMagick] on every descent GNU/Linux distribution).
The very simple animation above has been obtained
euro-flag.mp with an input file named
animate.mp. A bash script named
animate-script is produced during MetaPost execution that fits the very particular list of figures. Bashing this script would produce the animated gif above. Below, a rather complex example.
Here is another animation (turning associahedron) made with the m3D programs. It also illustrates the use of pseudo-transparency with metapost.