Out Of Bounds
The "Out of Bounds" (OoB) area is any area outside of the intended play area of the map. A more specific definition for Portal is that OoB is any area where you can get stuck by jumping or falling if there is not a portal on a surface nearby. OoB tricks are used in Portal to skip massive portions of the game, but are not limited to just Portal.
In the BSP map format used by the Source engine, brushes have a front and a backside; Being OoB reveals the backsides of the brushes, causing visual glitches.
Out of Bounds Glitches in Portal
Out of Bounds is most useful in Portal, allowing the player to skip massive portions of the game. There are a number of methods for getting OoB, including:
The most commonly used of these methods in the current speedrun route is the clipping glitch, due to its ability to be used almost anywhere and the speed with which it can be performed.
Traveling OoB is generally done by placing portals on the outer surface of the level and moving quickly towards the end of the level, but other methods of movement exist. It is possible to walk along the top of levels, but the player must be careful not to jump or they will get stuck for a brief period of time. Further, the player will get stuck if they fall a short distance without a nearby portal. However, you can use this to your advantage by getting stuck next to a portalable wall that would otherwise be difficult to access. This is used in Portal Done Pro-er in escape_00.
The Out of Bounds area is useful for travel, but to gain any benefit from OoB movement you have to be able to get back into the intended playable area. There are a number of methods for reentry as well:
- Portal Bisection Fallthrough (PBF)
- Portal Destruction Reentry (PDR)
- Portal Quick Reentry (PQR)
- Portal Bumping
- Fizzler Reentry
- Save and Load Reentry
The most commonly used are PDR and PQR due to their speed and relative ease of use.