Although there are a couple particle system libraries available for Processing I thought I’d build my own anyway. For practice, a better understanding of what’s going on, and more control over the details. With a little help from Dan Shiffman I began working on one a little while ago but never quite finished it. Trying to extend my Wave script to flow fully in two dimensions, a particle system seemed like a good tool. All the particles repel each other and have realistic motion with force, acceleration, and velocity vectors. I also added a spring class and a few other little tools.
On the way I was distracted a few times and made a few other generative sketches. This one simply creates particles which slowly fade. A curve along all of the points with a very low opacity creates the brushy textures.