2009

At the heart of the system are the Crowd and Delegate helper objects. A single

Crowd object can control any number of delegates, which serve as stand-ins

for crowd members. You can group delegates into teams, and assign behaviors

such as Seek, Avoid, and Wander to individuals or teams. You can combine

behaviors with weighting, so that, for example, a crowd member could seek

a goal while wandering slightly.

Crowd simulations can range in sophistication from simple and straightforward

to highly complex. Aiding at the latter end of the range is the Cognitive

Controller feature, which lets you use the scripts to apply conditional

transitions to sequences of behaviors. For example, you could tell a delegate

to approach a goal until it gets within a certain distance, and then start moving

away. Or you could use a Cognitive Controller to have a delegate move among

a series of goals.

Another means of creating complex, dynamic crowd simulations is motion

synthesis, which can be used in conjunction with the Cognitive Controller.

The Crowd system offers two types of motion synthesis.

■ When working with bipeds, you use the Motion Flow feature to allow the

software to create scripts for the bipeds that match the delegate behaviors.

■ When working with non-bipedal characters, such as fish or birds, you use

Clip Controllers that let you apply different animation segments to various

types of motion. For example, a bird flaps its wings quickly while ascending

but slowly while flying level, and stops flapping its wings during descent.

One of the most important requirements of crowd simulations is avoidance;

if characters pass through each other or other objects in the scene, realism

suffers. The Crowd system offers various behaviors to help achieve proper

avoidance. It also provides the Vector Field, a special space warp, which, when

applied to an irregularly shaped object, allows delegates to move around the

object without penetrating it.

Used in combination, the Crowd-system tools described here can produce an

endless variety of interesting, multi-character simulations. The Crowd topics

in this manual provide detailed information about every aspect of crowd

simulation.