Chris Jurney, a senior programmer for Relic, offered the example of the state machines in its RTS, Dawn of War 2, to illustrate this. "The AI for Dawn of War 2 has roughly three main layers: the computer player, the squad and the entity," says Jurney. "The squad and the entities are both hierarchal finite state machines, and we have roughly 20 states at the squad level and 20 at the entity level. The states at the squad level pretty much map directly to orders that can be issued by the user.
"For example, if you issue a capture order to a squad, the squad will enter the SquadStateCapture state," continues Jurney. "This state might find that it’s not close enough yet to capture the point, so it will sub-state to SquadStateMove. In this state, the formation movement system will kick in and start issuing Move orders to individual entities, and the entities receive these commands and enter the StateMove state. Inside that, paths are found, dynamics are applied and generally, the individuals try to look smart as they perform their orders."
Some states will also be shared among multiple character types where relevant, and most characters spend most of their time using just a few standard states, with the others waiting in the wings for extraordinary circumstances.
