Line-of-Sight Detection

Each guard carries a facing and a cone or radius of vision, and detection becomes a question of geometry: where the player stands, what lies between them, whether the guard has turned. Sightlines break on walls, cover, distance and darkness. Because knowledge is held per character rather than globally, one room can contain several conflicting beliefs about it, and manipulating those beliefs is the actual gameplay.

Muse Software built Castle Wolfenstein in 1981 around guards who could be avoided rather than only fought, a pointed idea when most games modelled opponents as pursuers that always knew the player's position. Memory constraints helped, since a facing and a short check are cheap. Design intent mattered more: a game about escaping a fortress needs enemies whose attention is a resource to be managed.

An entire genre followed, along with a broader principle that combat can be a failure state rather than a goal. Legibility and fragility are the costs. Players cannot see a vision cone unless the game draws one, so detections often feel unfair, and such systems break memorably when a guard spots a body through a wall or forgets a firefight. Modern versions spend heavily on communicating what enemies perceive.