Walkers wander one cell at a time in a random direction. The first time one touches the crystal it freezes there. That is the whole rule.
Tap to move the growth centre and plant a seed there. The crystal regrows when it reaches the edge. The same ?seed= always gives the same run.
LITDiffusion-limited aggregation (Witten & Sander 1981). Every 60 steps the frozen count must equal the frozen cells on the grid, or the page throws.
AMBERThe dimension shown is a rough ln N / ln r estimate, not a fit.