Game Development Reference
In-Depth Information
chapter 8
Emergent Behavior
One of the more welcome outcomes in computer AI is emergent behavior. It is
very well suited to control simulated flocks of birds or crowds of people. For our
purposes, we will bend the classical definition of emergence to mean behaviors
that were not explicitly programmed into individual software agents but are
exhibited by a group of interacting agents. Early examples are found in the video
Eurythmy produced at the Ohio State University Computer Graphics Research
Group [Girard85] and in Craig Reynolds' ''boids,'' used to make Stanley and
Stella in: Breaking the Ice [Reynolds87]. Since then, countless others have made
use of this technology in movies and games.
The impact of the emergent behavior that arises from simple steering forces is
best experienced with animated visual media. The Lord of the Rings movies are so
engaging as films that it is difficult to study the computer-generated hordes in
motion, but the boids demonstration on Craig Reynolds' Web site [Reynolds01]
is accessible to anyone with a Java-enabled browser. The paper airplane-shaped
triangles are not particularly engaging, but the motion they exhibit certainly is.
For anyone who has never seen the demonstration, a few minutes watching the
motion and a glance at the explanation would be time well-spent.
Emergence is a welcome technology for two main reasons: It looks very realistic,
and it can be computationally cheap. Reynolds programmed three simple
behaviors into each boid. These behaviors told each boid to stay with its local
group, to go where its local group is going, and to avoid getting too close to
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