Behavioral Animation - Computer Animation: Algorithms and Techniques - page 338

CHAPTER

11

Behavioral Animation

As discussed in the previous chapters, there are a variety of ways to specify motion. Some are very
direct. In key-frame animations, for example, the animator precisely specifies values for animation
parameters as specific frames and selects an interpolation procedure to fill in the remaining values
for the in-between frames. There is not much mystery as to what the parametric values will be or what
the motion will look like. In physically based animation, such as rigid body dynamics, the animator
might specify starting values for some of physical simulation parameters, for example, initial position
and velocity. The animator generally knows what the animation will look like but does not have a good
idea of the intermediate parametric values as an object falls, collides, and bounces. This is an example
of model-based animation where there is an underlying model controlling the motion. In this case the
model is physics—or at least some approximation to it.
Behavioral animation is another type of model-based animation in which it is the cognitive
processes that are beingmodeled. The term cognitive process refers to any behavior that can be attributed
to mental activity, voluntary or involuntary, that is reacting to the environment—basically
non-physically based procedural motion. The cognitive processes can be as simple as moving toward
a light or as complex as balancing self-preservation, mood swings, and personality disorders.
Whereas modeling complex cognitive processes might be necessary for creating a believable autono-
mous character in a game, simple cognitive processes are often sufficient for modeling crowd behavior.
Development of behavioral animationhas beenmotivated by applications of virtual reality (VR), computer
games, military simulations, and the film industry. Behavioral animation can be used to evaluate environ-
mental design suchas escape facilities ina burningbuilding. It alsocanbeused tocreatemassive crowds for
films, to supply background animation, or to provide stimulus for virtual environments.
Modeling behavior can be useful for several reasons:

￿ To relieve the animator from dealing with details when background animation is not of primary
importance
￿ To generate animation on the fly, as in a game or VR application
￿ To inspect the results of a simulation, that is, to evaluate the environment relative to a certain behavior
￿ To populate virtual environments

Synthetic characters with built-in rules of behavior are often referred to as actors or intelligence
agents . When a figure is meant to be the embodiment of a user in a virtual environment, the term
avatar

1 is often used.

1 In Hindu mythology, an avatar is an incarnation of a deity (especially Vishnu) in human or animal form.