Two chemicals U and V diffuse and react on a wrapping grid. The classic parameter set Du=0.16, Dv=0.08, feed=0.035, kill=0.062 grows organic spot / maze patterns from a central seed.
Click / drag on the canvas to inject V and deplete U near the pointer — new patterns will grow from there. Toroidal (wrapping) boundaries: patterns leaving one edge re-enter the opposite side.