Authoring Background Character Responses to Foreground Characters

This paper presents a flexible and intuitive authoring interface for specifying the behaviors of background characters and their reactions to user-controlled foreground characters. We use an event-centric behavior authoring paradigm and provide metaphors for altering the behavioral responses using conditions, modifiers, and contexts. The execution of an event (an interaction between multiple characters in the scene) is governed using authored conditions on the state of the participating characters, as well as the history of their past interactions. Our system monitors the ongoing simulation and the actions of foreground characters to trigger plausible reactions in the background characters as events, which satisfy user-authored conditions. Modifiers allow authors to vary how events are perceived by specific characters, to elicit unique responses. Contexts provide a simple mechanism to add behavior modifiers based on the current location of the characters. We demonstrate the benefits of our approach by authoring a virtual populace, and show the design of simple background activity, to more complex multi-agent interactions, that highlight the ease and flexibility of specification.