I’ve recently implemented zone culling portals which will get used mostly by indoor scenes. Portals are something like gates or windows which connect places. They are usually represented by 2D shapes. Their function is simple: If the player resides at one zone, he can only see and move to a neighboring zone through an existing portal between both zones. On this way it is possible to skip invisible zones and attached geometries inside.
Portals are very powerful due to some new possibilities
- Visibility culling: Connection of indoor and outdoor scenes, room to room connections. Visibility control (e.g. door opening/closing, LOD)
- Interactive content paging: That means no annoying loading zones are needed. Portals can serve as hint to load required content on the fly.
- Coordinate switching and axis reorientation: Makes things possible like gravity direction redefinition, wrapped or infinite geometry.
- Stencil culling through shapes makes effects possible like wormholes.