The Processing code above is based on the logic implemented in this code I posted before. I just added some random attractors, timing for agents continous initialization and a function to render the field properly. What you get with this code is (a sort of) simulation of percolation. What's interesting I guess is that you can watch the landscape continously changing over time.
The code is written for Processing 2.0 and You will need Toxiclibs and ControlP5.
N : turn on/off agent preview
T : turn on/off agent tail preview
D : turn on/off landscape preview
You can have a look at the code on my Git.
Below some screen captures of the code running: