Topics for Today • Task planning for non-player characters • Coping with player character interactions and their effect on narrative • Robots as believable characters
Creating Characters • How to design/develop the characters in interactive stories? • Characters in games have routines and respond to triggers • We want more depth, like in written scripts (e.g. books, tv, movies) but interactive • What makes characters in traditional media believable?
The Friends Engine • Character-based storytelling • Story emerges from interaction among autonomous characters • Planning • Hierarchical task network (HTN) • Interaction? • Changes to the environment (objects in environment) • Talking to character (to give information, instructions, advice)
High-level design • Original intent/design like audience yelling to actors • Character actions driven by goal(s) • Goals can be achieved through alternative sets/sequences of actions • Environmental features and other characters can affect if a action is successful • Interleaving planning with execution and opportunities for interaction
Planning Engine • Actions have weights attached describing their characteristics (sociability, rudeness) • Character traits use these weights when selecting among alternative actions • Different characters would try different plans • Total order HTN planning to reduce/remove task interaction • Tries to avoid the crazy wolf scenario where character rapidly switches back and forth between two plans
Interaction with World • User as spectator • Can explore the space via invisible avatar • Cannot interfere with characters directly • Can interact with objects in space • Can cause replanning by characters • “Butterfly effect” • Inconsequential changes can cause narrative changes indirectly
Communication with Characters • Natural language intervention • Templates for • Instructions (“talk to Pheobe”) • Information (“the diary is in the living room”) • Advice (“be nice to Pheobe”) • Heuristics to differentiate types of advice and instructions • Negative statements tend to be generic advice (“don’t be rude”) • Positive statements are more likely to be instructions (“talk to Monica”)
Summary • Task modeling to enable weighting of activities and options • Human interaction with characters related to activities and options
User as Character • Interactive Narrative-Oriented Systems • Users interact with animated agents in virtual world • User’s actions can affect narrative • User has partial knowledge of narrative • Must manage actions to ensure story continues • How to identify problems and their resolution?
Control and Coherence • Competing goals • Control • Increases engagement • Not interactive without some control • Coherence • Scenes and actions should relate to the overall story • User actions can alter/break the story
Mimesis Planning and Architecture • Hierarchical partial-order planner • Requires representation of all actions possible by all characters (including user) • Causal links • Connects plan steps with condition
Monitoring User Activity • User activity must be evaluated with respect to the planned narrative • Constituent to the plan • Matches some action in the plan • Consistent with the plan • Not part of but does not interfere with plan • Exceptional to the plan • Interferes with plan • System must recognize exceptions and respond
Responding to Exceptions • Accommodation • Let the user’s action stand • Replan to keep narrative • Example: user does not go to planned location • Response: find an appropriate alternative location • Example: user discards weapon • Response: non-player character finds weapon or a different weapon is chosen • Accommodation may not always be possible
Intervention • Replace user action with a failure mode instance of the action • Example of coin and vending machine • Broken machine • Could have created second coin … • Mimesis constructs table with all possible exceptions and mediation policy • Only possible because of having representation of all possible user actions
Run-Time Management • Execution Manager receives plan and table of mediation policies • Non-player characters go about initial plan • System waits for user to begin their constituent actions and watches for exceptions
Questions • Consider yourself as user. How would you react to such intervention? What would your reaction depend on? • How does this compare to what you would expect in the imagined holodeck?
Mannequin http://www.youtube.com/watch?v=t8kcTFLNz0w • Summit http://www.youtube.com/watch?v=oAN7vAp2FfU