Since Valve announced Left 4 Dead 2, the feature of the AI Director 2.0 that grabbed the most attention has to be the dynamically changing level geometry. Apparently the game can not only control the weather patterns, but it can also change the route the survivors take while moving through the world.
In this article, you'll find out exactly how the AI Director 2.0 adapts the geometry procedurally. There's also proof in the form of exclusive screenshots from the demo of L4D2, which was released to the general public a few days ago. (The screenshots are exclusive in the sense that I took them myself, and nobody else has these!)
(Special thanks to @RevFry on Twitter for helping isolate all these variations.)
How It Works
Last week we held a Zombie AI Halloween Special, in which Phil Carlisle and I (Alex Champandard) speculated how L4D2 would handle the procedural geometry. Based on our combined experience, and the in-depth Premium feature I wrote about the original AI Director in Left 4 Dead 1, it turns out we came really close.
Here's how it works:
There are individual variations in the geometry that are manually edited by level designers.
These are grouped into sets of possibilities for the geometry around a particular location in the level.
The AI Director uses it's pseudo-random selection among these sets to determine what happens in each game.
This approach is very similar to the way the AI Director handled the placement of scavenge items and weapons in the original game, allowing control by the designers yet sufficient unpredictability to keep things interesting.
The only part that wasn't easy to guess was the scale at which the levels would be varied. Phil assumed there would be small rooms or segments in the world that would change, and I figured doors and fences would be the easiest way to introduce variation into the levels.
Based on the demo so far, the AI Director 20 is indeed using boarded doors, riot fences, and walls to block off alleys. In this part of the first level, there are three different paths the survivors can take. From experimental evidence, 1-2 of these paths are left open and the other 1-2 are closed off procedurally. This seems to happen only in Advanced and Expert modes.
(See the screenshots below. Click to enlarge.)
Anyway, based on this we can start speculating about the rest of Left 4 Dead 2!
Do you expect there to be larger segments of geometry that change in the full version?
Will such local path changes (barely 10-20 meters difference) affects the gameplay enough?
How do you think this kind of technology can be applied to other games or genres?
Let everyone know what you think and post your reply by commenting in the forums.