Environment-based physical motion for secondary characters

Motion pictures of all sorts make heavy use of "extra" actors to bring fidelity and liveliness to a scene. These secondary characters are usually engaged in low-energy, background actions and are often seen close-up and in-detail. This fabric of background human activity comes with two main challenges. First, secondary characters must be able to react to events in their environment. Second, characters should not exhibit motions that are too repetitive. In this paper, we propose an approach to generating physically realistic and non-repetitive motion for small groups of autonomous secondary characters. To equip a character with a wide range of motor skills we introduce the concepts of behavior and transition. A behavior models the ability of a character to remain within range of a set of well-defined configurations, while a transition allows the character to change its behavior. Characters choose their behavior as a response to the environment and in accordance to a simple physiological model.