Golan Levin is an artist and engineer. He creates interactive works of art, many times using programs exactly similar to processing. In this TED talk he describes some of his work. One of the things that was more interesting that he talked about was an art display where anytime a loop or closed figure was made by the silhouette of people, it formed a shape which then dropped due to gravity.
Here you see some images of the type of interactivity that was created. Another project he did was placing a large eyeball figure on top of a roof and had it react to people walking up to the building, always making a surprised look through its form.