[NTG-context] Metapost animation

Hi Hans, hi all, in an former mail you had answered to the question of Michal Kvasnicka: "Is it possible to `animate'

the fieldstack? In other words, to make it change one figure to another automatically, without clicking anywhere, changing one frame to another each 1/n second to simulate a smoth motion like in a cinema?":

"sure, you can let a javascript toggle the states, ...". Has someone already experience with such animated field stacks and can give me some clue how to realize this? With many thanks in advance Albrecht