Portal visibility

From DmWiki

Portal visibility is one method of reducing the number of polygons that need to be rendered each frame. It is best suited to indoor, hallway-type games.

Portal visibility works by dividing the world up into a set of convex, connected regions. The invisible boundaries between these regions are called portals. For instance, a room might be a single region, and a doorway would be a portal. Portals are sometimes placed by hand, but are more frequently generated using an automated tool, often using a BSP tree.

Once portals are in place, rendering can proceed in front-to-back order. First, the region in which the camera lies is rendered. Then, any visible portals in this region are identified, and the regions on the other sides of these portals are rendered. Then the process repeats: visible portals in the regions just rendered are identified, and more regions are rendered on the other sides of these portals. Rendering is complete when no portals are visible.

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