In computer-generated imagery and real-time 3D computer graphics, portal rendering is an algorithm for visibility determination.
By determining which polygons are currently not visible, and not rendering those objects, significant performance improvements can be achieved.
Regions of map space are divided into polygonal, generally convex, areas called zones, or sometimes sectors.
Adjacent zones are linked to one another via shared dividing polygons termed portals.
[3] The use of portals simplifies the game engine's task of determining visible areas and objects from any given point of view of the level, and simplifies rendering by allowing it to use each portal as a viewing frustum for the area it leads to.