The Processing sketch from which the frame above was taken now has a name: Seurat. It has controls (radius and frame rate) that can be operated by the slider (linear potentiometer) and the joystick on an Arduino Esplora board. Arduino reads the sensor data and sends it to Processing over the serial (USB) port.
Code for Seurat | Code for Arduino
The next step in this project is to build a box with lots of knobs and switches to control Seurat via a standard Arduino board.
Credits: Jeremy Blum’s blog was a great help in figuring out how to make Arduino talk to Processing. Mark Frauenfelder post at boingboing.net has a useful (and fun) video on how to make a good enclosure for the electronics.