A Processing 3 sketch of four slowly evolving polygons and a meditative soundscape created by a few Tibetan Singing Bowls.

The algorithm is very simple:

• place each vertex of each polygon in a random position
• assign to each vertex a random direction (all polygons have the same scalar velocity)
• at every frame move each vertex, if the new position is outside a border, simply make it bounce (reverse the velocity component orthogonal to the border)
• assign a different color to each polygon and draw only its outer border (no fill)

The source code can be dowloaded here.

I made a video of the animation (starting from 4 rectangles) and added a soundscape made with sampled Tibetan Singing Bowls.

Other implementation ideas:

• change the speed of each vertex
• slowly change the color of each polygon
• generate a MIDI message each time a vertex hits a border and send it to a virtual instrument or synth

If you improve the code or implement other variations let me know in the comments below.