Casting Digital Extras

Dr. Paul A. KruszewskiPresident, GRIP

Overview• Where we are coming from• Where we are at• Where we are going

Who is GRIP?• A game AI software company in Montreal

• The guys who created AI.implant• 2002 Best AI tool (Game Developer Magazine Frontline Award)• 2006 Best middleware (Game Developer Magazine Frontline Award)

• GRIP credits include• Army of TWO: the 40th day™, Deus Ex 3, Tron:evolution

• GRIP customers include• Autodesk, BioWare, Disney, EA, Eidos & Intel

What Does GRIP do?• Develop next-gen game AI products for AAA games

• Digital Extra System• Crowd simulator

• “real-time Massive for games”

• Character Control System• High level NPC AI

• “MS Dev for game brains”

What is an Extra?• Like a movie extra

• Anyone you are not supposed to deeply interact with

• The more the interactivity, the less its an extra

• “Clutter”

• Background characters

• Aesthetic

• Large numbers

• Computationally cheap

• Controlled en masse

Shipped Examples• Army of TWO: the 40th day• Tron:evolution

Core Elements• Core behaviour

• Mill around and interact with the ambient world

• Be aware of other people including player

• Panic when a bad thing happens

• Required tech• Flows

• Obstacle avoidance

• Action stations

• Spawners

• Brains

Flows• Goal

• Have lots of people move around a world seemingly with purpose

• Problems• Computationally slow; Little control; Sidewalk problem

• Method• Flow network tells extras where to go

• Advantages• Computationally simple and cheap; Expressive: extras go where they are

told

• Rocket Science• Dynamic lane forming; Dynamic splines

Obstacle Avoidance• Goal

• Have extras avoid running into each other in a natural looking way

• Problems• Twitching; Getting stuck (piling up)

• Method• Case sensitive steering behaviours; Social rules / self organizing lanes; Tie into the

animation system

• Advantages• Very robust; Looks good

• Rocket Science• Knowing when to stop and circumvent

Action Stations• Goal• Add variety and realism to the movement behaviours by adding animations to show

interactivity with environment

• Problems• Scalability • Interpretability

• Method• Smart objects that suck extras off flows and play animations that look like complex

behaviours

• Advantages• Looks good. Most AI behaviours are actually animations; Scales with animators not

programmers

• Rocket Science• Context switching / interrupting; pathological players; queuing

Spawners• Goal

• Maximize the user’s perception of the extras

• Problems• Pre-roll; Spacing

• Method• Spawn on point / zone / flow; Despawn into pools

• Advantages• Precise control of user experience

• Rocket Science• A million little details

Brain Authoring• Goal

• Create behaviours of increasing complexity

• Problems• State machines: state explosion; Script / coding: too unconstrained / requires highly

specializes skills; Planners: incomprehensible

• Method• Behaviour trees; Graphic editor / debugger

• Advantages• Coder / designer literally on the same page; Encourages scalability, modularity and re-use

• Rocket Science• Control flow / exception & interrupt handling / blackboard

Future Directions• Greater Fidelity

• Transitions to NPCs

• Props

• Greater Breadth• Ambient vehicles

• Different engines