6.370 Home: Background: Primer: Definition

The general definition of a game is a set of initial states, a set of end states, and constraints/rules for changing state. End states are considered either winning/goal states or losing states; for simplicity there are no draws. An instance of a game is a specific sequence of states from a particular initial state to a particular end state. Games that have similar goals, constraints, and state compositions comprise a genre. For RTS, state is a map and all the units, buildings, and resources on it, together with their own states. Electronic games formalise these constraints in software and represent game state on a display device.

In realtime strategy (RTS) games, the strategy part refers to the control of units, buildings, and resources on a map from a high-level, omniscient view; the deployment of armies on land or fleets across a galaxy, for example. This view is usually a three-quarters-up third-person view in traditional 2D RTS games. This is a major difference from first-person-shooters (FPS), such as Doom and Quake from id Software and Unreal from Epic Games, which are mostly concerned with combat on the basis of an individual or group of cooperating individuals. There is also a subtle difference between RTS and realtime god games, such as Peter Molyneux's Black & White from Lionhead Studios or the Creatures series, which are more concerned with human interaction with a virtual world over long instances rather than with player interactions in shorter, isolated instances.

Three-quarters-up third-person view in StarCraft		First-person view in Quake III

The realtime part refers to the feature that all of your actions have immediate consequences visible to all players, and vice versa. In turn-based strategy, you can ponder your options carefully before making a move; if you do this in RTS, your opponent will most likely flatten you in short order (and your pointy little thinking cap, too). Examples of the older turn-based genre are Sid Meier's Civilization III or Alpha Centauri from Firaxis, the Heroes of Might and Magic series from 3DO, the famous SimCity series from Maxis, and board/card games, like chess or hearts.

A hurricane damages your town in SimCity 3000.		Empire-planning in Civilization III.

To win at RTS, a player must be quick (possessing skill in realtime) and must know all the constraints (possessing skill in strategy). However, it is much more common to make a game more strategic (by adding more constraints) than it is to make a game more realtime. Thus, game designers create expansion packs by adding new units and abilities; new buildings and tech tree dependencies; new resources; and new terrains and maps to the original game. We will discuss each of these components in the following sections. The right amount of complexity will make the game challenging enough to be interesting but not tedious enough to require encyclopedic knowledge of all constraints.

In RTS, the goal is a preferred state of the map, which can involve the location of some special object (capture-the-flag), the removal of a special unit (regicide), or usually the removal of all enemy units and buildings; the strategy part also means that the rules for achieving the goal state usually involve the so-called "harvest, build, destroy" model; in other words, the simulation of economic, technological, and military constraints.