Cellular automata is an n-dimensional set of cells that interact together with a given set of rules. Over time, these interactions have given way to patterns, and modifying the rules will modify the pattern. The most famous example is probably Conway's Game of Life where cells based on an extremely simple rule set create the most amazing, evolving patterns. In games, cellular automata is usually found simulating liquids in a tile– or block–based game worlds.
In this recipe, we'll explore such a liquid system based on a 2D grid. Since it's 2D, there can be no true waterfalls, but it can still be applied to a heightmap (which we'll show) to create natural-looking rivers.
Performance becomes an issue with large cellular automata, which will become evident as they're scaled up. To counter this, we'll also look at a couple of different techniques to keep the resource consumption down. The following image shows water running down the slope of a mountain:
