Choose particle shape you think makes best frost fern. Particles (light blue) start at random top positions, move down until touching a stationary particle (white).
Similar patterns seen in crystal formation, coral, fungi growth, liquid seeping through soil, lightning, or dye spreading in glue. A process called diffusion-limited aggregation (DLA) creates patterns much like these. I modified this from my earlier coral and DLA project from a couple years ago. I tried a different way of window frosting here: https://scratch.mit.edu/projects/635586780/