Propagating Fire and Fluids

Spread is simulated across a grid of flammable material. Each burning cell has some chance of igniting its neighbours, weighted by wind direction, slope and fuel density, and burnt cells are consumed so a fire eventually runs out of ground. Because the rules are local and continuous, behaviour at the scale of a hillside is genuinely unpredictable, and one match can clear an ambush or trap the person who lit it.

Ubisoft Montreal built fire propagation into Far Cry 2 in 2008 as the centrepiece of an open world about improvisation. Its savannah setting supplied both dry grass and a reason for the player to be carrying incendiary weapons, and the simulation let a single flare replace an authored assault plan. Wind direction was made visible in the world specifically so the system could be used deliberately rather than merely survived.

Emergent hazards are a bargain: what players gain in tools, designers lose in control, since encounters can end before they start and scripted scenes can burn down around them. Cost is computational as well, which is why later games often confine propagation to designated areas. Where it survives, it survives because a system the player can weaponise makes a world feel indifferent rather than staged.