Random Walk

What it does

A circle starts at the centre of a grid and picks a direction at random every frame — up, down, left or right — rejecting any move that would take it off the grid. Each cell counts how many times it has been visited and is drawn more opaque the more often it is crossed, so the path the walker has taken builds up over time. The routes near the centre are travelled most, so they show brightest.

The leading circle cycles through hues as it goes, so the current position stays visible against the accumulated trail.