Games Demystified: Portal

[In the second in this series of articles which deconstructs a particularly fun or interesting mechanic in a recent, relevant game, Jeremy Alessi pulls apart Valve's Portal and puts it back together again -- to give us a clearer understanding of the compellingly-executed teleportation mechanics central to that game's astoundingly entertaining gameplay.]

EDITOR'S NOTE: To download the associated demo and code sample for Portal Demystified, please click here.

Welcome back to Games Demystified. This month we'll be examining the chief gameplay mechanic behind last year's amazing Portal! Anyone who's played Portal has heard GLaDOS state, "Speedy thing goes in, speedy thing comes out".

That line sums up the mechanics that distinguished Portal from the rest of the herd this past winter. Sure, the impressive story and rendering also had a part, but it's simply not a game without the mechanics.

Game mechanics are usually abstractions based on real-world physics. In the previous Games Demystified column, we covered gravity as it was applied in Super Mario Galaxy, a force that is mostly unexplainable and yet tremendously fun with the proper application in gameplay.

This go-round we're looking at wormholes, Einstein-Rosen Bridges, or portals, if you will. These phenomena are predicted by Einstein's theory of General Relativity.

Image From Samuel Joseph George's description of The Einstein-Rosen Bridge

Like gravity, Einstein-Rosen Bridges are mostly a mystery. Perhaps someday through imagination and cool video games we'll gain a proper understanding. Until then, we've got a nice pseudo-laboratory in Portal to experiment with these mechanics.

Just playing the game is a mind-trip. Exactly how can we simulate a tunnel or wormhole through the fabric of space-time? How do we do speedy-in, speedy-out, momentum redirection -- or "flinging", as Valve calls it?

Teleport mechanics in video games are nothing new. Puzzles from the original Gauntlet were memorable -- and more than likely, that wasn't the first game to use teleportation as a gameplay mechanic. The difference between Portal and all those that came before it is that Portal's teleportation acts as a frictionless tube between point A and point B.

Physics are still hard at work inside the frictionless tube. Instead of simply repositioning an object from point A to point B, the player enters point A with full velocity and exits point B with the same speed, but moving in a new direction.