What are Portals?

#1 Portals are for visibility determination and culling in realtime.

Check the portal engine series over at flipcode for more information.

#2 Ok, thanks. That helps clear things up.

Now for the same question as applied to Torque, What purpose do portal's serve?

#3 Charles,

To put it simply, the portals allow you to block off different sections of your interior into different zones. Anything in these zones will only get rendered if you can see the zone(or rather, a portal of the zone), thus reducing the amount of polygons you render significantly.

You typically block off areas with portals, e.g for a room, you'd block off the doorways leading into that room. The map2dif program does the rest building the zones, etc.

#4 Efficiency is key in realtime environments, Portals, LOD, and many other optimizations exist purely to reduce the number of excess polygons that might be rendered when they don't contribute to what the player sees.

Portals prevent sections of interiors that the player can't see from being rendered.

Levels of detail reduce the number of polygons that render when an object is far in the distance.

#5 So whats the difference between portal, bsp and octree or similar technics?, and which used by torque?.

#6 Torque uses all three techniques. They are all means of partitioning space. Portal does it by having the artists divide the world into enclosed chunks. Torque uses this for interiors. BSP does it by cutting the world up along planes of polygons, so that it's always possible to sort the world from back to front for rendering (or more often collision checks). Torque uses this technique for a variety of smaller tasks, including shadow calculations and transparent object sorting. Octree techniques divide the world up into a bunch of nested bounding volumes - like a grid of boxes. Torque uses this for quick collision culling.

#7 Ok man that was too useful, thanks.