Game Development Reference
In-Depth Information
systems stable, but too much of it yields the ultimate in order in which nothing
It should be obvious that stable systems need a balance between positive and
negative feedback. Boids balance the need to stay with the flock against the need
to avoid overcrowding. When designing a stable system with emergent behavior
in mind, you should examine the interaction behaviors. Every positive-feedback
input is a potential source of instability; it must be balanced in some manner.
With a few simple behaviors, it should be easy to prove that the system will find a
balance point. As the number of behaviors increases, proof becomes impossibly
hard. The programmer is reduced to ''flight testing'' the system, looking for a
stable regime and then programming in guards against excursions outside the
stable envelope.
Both kinds of feedback are beneficial in emergent systems. Positive feedback
drives emergence, and negative feedback keeps it from going out of control.
Hidden in all of this is the effect of timing. How fast should the feedback loops
operate? It should come as no surprise that the answer is neither too fast nor too
slow, but just right. Our project simulation can provide some concrete insights
into timing.
Fast Feedback
In the military, feedback is known as a decision loop , and the Holy Grail is to have
a faster decision loop than the enemy. The idea is that the fast side acts, forcing
the slow side to react. The fast side can then turn that reaction into a mistake
before the slow side can adapt. If the advantage is extreme, the fast side can avoid
destructive force-on-force styles of combat and still defeat the enemy. This
works, however, only if the forces of the fast-thinking side are nimble enough to
exploit the advantages of thinking faster. Many systems can think faster than they
can act.
Faster feedback is not always better. Computer games need to stay at human-
compatible speeds. In the case of boids, if the reaction times are too short, the
flock will appear to vibrate instead of undulate. Short times imply higher fre-
quencies, and at some point the frequency is too fast for human perception.
Shorter feedback loops also carry an inherent disadvantage even if the system
would benefit from them. Faster and faster feedback tends to result in decisions
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