Examining Portal's Teleportation Code

Gamasutra is running a story deconstructing the mechanics of Portal's teleportation programming. They present a snippet of Portal's code and a downloadable demo. They ran another article in this series earlier this year with an analysis Mario Galaxy's unique take on physics. We've discussed the development of Portal in the past. "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." Update: 8/26 at 19:37 by SS: Dan notes that the code was not directly from Portal; it was written to approximate Portal's physics.

Comments

Portal Physics 101

[xPsi]

In the game, GlaDOS says "momentum is conserved through the portal." Assuming our physical system is the character, momentum definitely is not conserved. Neither is energy. The description "the player enters point A with full velocity and exits point B with the same speed, but moving in a new direction" is exactly correct: a textbook example of momentum non-conservation. However, what drives the exciting "flinging" effect, which makes Portal's teleportation so unique, isn't just momentum redirection. It's that you instantly obtain the potential energy of your exit location. This new potential energy can be converted back into kinetic energy, increasing your speed...mix in a little momentum redirection at the portals then wash, rinse, repeat. Although GlaDOS describes the game physics incorrectly, there is a game walkthrough where the programmers do describe it correctly. If you take any physics courses from me, you can expect to see some Portal questions on future quizzes :) Nice article overall.