Topics for Today Task planning for non-player characters Coping with player character interactions and their effect on narrative In Hamlet on the Holodeck, many issues related to character development and player’s interactions with characters/narratives were discussed – But how do we implement real solutions?

Rich Gold’s Little Computer People: Sega 1985

Will Wright’s The Sims (2000), The Sims 2 (2004), and The Sims 3 (2009)

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

Preserving Narratives with Player Characters

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

Accommodation example

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?