This is a geometric model of snowflake growth inspired by Kenneth G. Libbrecht's book Snow Crystals. It can grow realistic(ish) looking snowflakes, such as the ones below:
The simulaiton is carefully optimized (avoids major GC collections, uses cache-friendly data structures, etc.) and can grow (from seed to fully grown) any one of the above snowflakes in around 9ms (Google Chrome, AMD Ryzen 9 7940HS w/ Radeon 7). My benchmarks show that its speed is currently bottlenecked by CanvasRenderingContext2D moveTo() and lineTo() calls, which means any future performance improvements will probably come in the form of rewriting the rendering code for the GPU.