Abstract: A room is a region of space, such as a volumetric cell, that is associated with certain objects that are potentially visible (or potentially not visible) when the camera lies within the room. The rooms are distinct from the objects that represent a scene. A preprocessing step checks whether the camera is within a room, and if so determines those objects of the scene that are potentially visible (or potentially not visible) from within the room. Only those objects that are potentially visible from within the room are then rendered for display.

Abstract: A shield is a piece of geometry, such as a rectangle, that defines active/inactive regions in the world coordinate system that depend upon the position and orientation of the camera with respect to the shield. The shield is distinct from the objects that represent the scene. A preprocessing step determines those objects (or portions of objects) of the scene that lie in the inactive region defined by each of the shields. Those objects (or portions of objects) that lie in the inactive region defined by each of the shields are forwarded to the graphics subsystem wherein the objects are rendered for display. On the other hand, those objects (or portions of objects) that lie in the active region defined by each of the shields are not forwarded to the graphics subsystem.