State-Based Scripting in
Jason Gregory
Generalist Programmer
Naughty Dog, Inc.
Monday, April 6, 2009

Agenda
• Introduction to game scripting
• Extending the game object model
• State script syntax
• Case studies from
Uncharted 2: Among Thieves
• Implementation discussion
• Summary and some tips
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Introduction to State Scripts
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Brief History of State Scripts
• Script system on Uncharted: Drake’s Fortune originally developed
for in-game cinematics (IGCs)
• Evolved into general gameplay scripting system
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Brief History of State Scripts
• UDF IGC system revamped for heavy
use on Uncharted 2: Among Thieves
• Inspirations:
 GOAL language used on Crash and Jak series
 State objects from God of War engine
TM
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Why Script?
• Scripting languages used in games since Quake C
• Primary benefits of script:
 Takes pressure off engineering team
 Code becomes data—rapid iteration
 Empowers content creators
 Key enabler of mod community
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Why Script?
• Scripting languages used in games since Quake C
• Primary benefits of script:
I feel empowered!
 Takes pressure off engineering team
 Code becomes data—rapid iteration
 Empowers content creators
 Key enabler of mod community
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Scripting Language Characteristics
• Two kinds of game scripting languages:
 data definition languages
 runtime languages
• Runtime scripting languages typically:
 interpreted by virtual machine (VM)
 simple and small—low overhead
 accessible to designers and other “non-programmers”
 powerful—one line of code = big impact
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Choice of Language
• At Naughty Dog, we make heavy use of both data definition
and runtime script
 Both based on PLT Scheme (a Lisp variant)
• Key benefits of Lisp-like languages:
 Easy to parse
 Data def and runtime code can be freely intermixed
 Powerful macro system—easy to define custom syntax
 Naughty Dog has a rich Lisp heritage—comfortable
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Choice of Language
• Of course you don’t have to use Lisp!
• Data definition languages:
 custom text format,
 Excel comma-separated values (.csv),
 XML, ...
• Runtime languages:
 Python, Lua, Pawn (Small C), OCaml, F#, ...
• Many popular engines already provide a scripting language:
 Quake C, UnrealScript, C# (XNA), ...
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Extending the Game Object Model
• Every game engine has some kind of game object model
 Defines all object types in game world
 Often (but not always) written in an object-oriented language
• Scripting language often used to extend the native object model
• Many ways to accomplish this...
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Game Object Model References
• Rob Fermier, “Creating a Data Driven Engine,” GDC, 2002
• Scott Bilas, “A Data-Driven Game Object System,” GDC, 2002
(http://www.drizzle.com/~scottb/gdc/game-objects.ppt)
• Alex Duran, “Building Object Systems: Features, Tradeoffs and
Pitfalls,” GDC, 2003
• Doug Church, “Object Systems,” presented at a game development
conference in Seoul, Korea, 2003
(http://chrishecker.com/images/6/6f/ObjSys.ppt)
• Jason Gregory, “Game Engine Architecture,” AK Peters, 2009
(http://gameenginebook.com)
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Unreal’s Approach
• UnrealScript tightly integrated with C++ object model
 Single-root class hierarchy with some add-on components
 Classes defined in UnrealScript (.uc)
 C++ header file (.h) automatically generated
 Implementation in C++ or entirely in UnrealScript
Pawn.h Actor
generate
Pawn.uc
Pawn.cpp
Info Pawn Pickup ...
implement
implement
Scout Vehicle ...
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Property-Centric / Componentized Designs
• Property-centric design used on Thief, Dungeon Siege, Age of
Mythology, Deus Ex 2 and others
 Game object just a unique id (UID)
 “Decorated” with various properties
(health, armor, weaponry, etc.)
 Property encapsulates data + behavior
Armor: Light
Health: 200
Object Weapon: BFG
(UID)
AI: PlayerAlly
Weapon: Pistol
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
SsTrackGroupProcess SsProcess ProcessGameObject DynLight CameraControl ...
Character SimpleEnOty ...
...
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
Objects
 host of add-on components that update
over Dme
Process
SsTrackGroupProcess SsProcess ProcessGameObject DynLight CameraControl ...
Character SimpleEnOty ...
...
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components Objects
with transform
and mesh
Process
SsTrackGroupProcess SsProcess ProcessGameObject DynLight CameraControl ...
Character SimpleEnOty ...
...
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components Base class for
all characters
Process
SsTrackGroupProcess SsProcess ProcessGameObject DynLight CameraControl ...
Character SimpleEnOty ...
...
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components Simple
animaDng
Process
object
SsTrackGroupProcess SsProcess ProcessGameObject DynLight CameraControl ...
Character SimpleEnOty ...
...
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
SsTrackGroupProcess SsProcess ProcessGameObject DynLight CameraControl ...
Character SimpleEnOty ...
Manages a State
Script instance ...
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
SsTrackGroupProcess SsProcess ProcessGameObject DynLight CameraControl ...
Manages a Character SimpleEnOty ...
chunk of
running script
...
code
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
SsProcess
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
SsProcess
SsInstance
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Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
ProcessGameObject
SsInstance DrawControl AnimControl ...
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Charter
• World editor for
Uncharted is called
Charter
 Place game objects
 Edit object
properties
 Control level
streaming
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Uncharted State Scripts
• State scripts similar in many respects to property-centric model...
 adds finite state machine (FSM) support
 not specifically tied to “properties”
 coarser-grained (one script per object)
• More like scripted extension to existing entity type...
 ... or a “director” that orchestrates actions of other entities
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Anatomy of a State Script
• A state script is comprised of:
 attributes
 states
• States define object’s behavior via runtime script code:
 response to events
 natural behavior over time (update event)
 transitional actions between states (begin/end events)
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Anatomy of a State Script
State Script 1
Variables
State A State Script 2
On Update Variables
On Event1
State C
State B On Begin
On Begin On Event4
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Anatomy of a State Script
State Script 1
Variables Event1
State A State Script 2
On Update Variables
On Event1
State C
State B On Begin
On Begin On Event4
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Anatomy of a State Script
State Script 1
Variables Event1
State A State Script 2
On Update Variables
On Event1
State C
go to
On Begin
State B State B
On Begin On Event4
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Anatomy of a State Script
State Script 1
Variables Event1
State A State Script 2
On Update Variables
On Event1
State C
go to
On Begin
State B State B
On Begin Event4 On Event4
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Instantiating a State Script
• Attached to a native (C++) game object: Game
Object
 designers extend or modify native
C++ object type State Script 1
 define entirely new object types
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Instantiating a State Script
• Attached to a native (C++) game object: Game
Object
 designers extend or modify native
C++ object type State Script 1
 define entirely new object types
• Attached to a trigger region:
 convex volume Trigger Region
 detects enter, exit and occupancy
State Script 2
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Instantiating State Scripts
SsProcess • Placed as stand-alone object:
State Script 3
 “director” orchestrates actions of
(stand‐alone) other objects (e.g. IGC)
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Instantiating State Scripts
SsProcess • Placed as stand-alone object:
State Script 3
 “director” orchestrates actions of
(stand‐alone) other objects (e.g. IGC)
• Associated with a task:
Task A
 task = check point
Task B1 Task B2  script manages associated task
 orchestrates AI encounters
Task C
State Script 4  controls player objectives
Task D
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Instantiating State Scripts
SsProcess • Placed as stand-alone object:
State Script 3
 “director” orchestrates actions of
(stand‐alone) other objects (e.g. IGC)
• Associated with a task:
Task A
 task = check point
Task B1 Task B2  script manages associated task
 orchestrates AI encounters
Task C
State Script 4  controls player objectives
Task D • Spawned by another state script
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State Script Syntax
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State Script Syntax
• State script defined as follows:
 Don’t let Lisp syntax throw you!
 Lisp syntax is all (parentheses)
(define-state-script ("kickable-gate")
 Think C/C++ { } blocks (state ("locked")
• Parenthesized blocks highly )
...
context-sensitive in Lisp/Scheme (state ("opening")
...
)
(state ("open")
...
)
)
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State Script Syntax
• State script defined as follows:
 Don’t let Lisp syntax throw you!
 Lisp syntax is all (parentheses)
(define-state-script ("kickable-gate")
 Think C/C++ { } blocks (state ("locked")
• Parenthesized blocks highly )
...
context-sensitive in Lisp/Scheme (state ("opening")
...
)
(state ("open")
...
)
)
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Monday, April 6, 2009

State Script Syntax
• State script defined as follows:
 Don’t let Lisp syntax throw you!
 Lisp syntax is all (parentheses)
(define-state-script ("kickable-gate")
 Think C/C++ { } blocks (state ("locked")
• Parenthesized blocks highly )
...
context-sensitive in Lisp/Scheme (state ("opening")
...
)
(state ("open")
...
)
)
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Monday, April 6, 2009

State Script Syntax
• State script defined as follows:
 Don’t let Lisp syntax throw you!
 Lisp syntax is all (parentheses)
(define-state-script ("kickable-gate")
 Think C/C++ { } blocks (state ("locked")
• Parenthesized blocks highly )
...
context-sensitive in Lisp/Scheme (state ("opening")
...
)
(state ("open")
...
)
)
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Event Handler Blocks
(define-state-script ("kickable-gate")
(state ("locked")
(on (event "kick")
... ;; handle "kick" event
• Each state contains zero or more )
(on (begin)
event handler blocks ... ;; do when state entered
)
(on (update)
... ;; do every frame
)
(on (end)
... ;; do when state exited
)
)
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Event Handler Blocks
(define-state-script ("kickable-gate")
(state ("locked")
(on (event "kick")
... ;; handle "kick" event
• Each state contains zero or more )
(on (begin)
event handler blocks ... ;; do when state entered
)
(on (update)
... ;; do every frame
)
(on (end)
... ;; do when state exited
)
)
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Event Handler Blocks
(define-state-script ("kickable-gate")
(state ("locked")
(on (event "kick")
... ;; handle "kick" event
• Each state contains zero or more )
(on (begin)
event handler blocks ... ;; do when state entered
)
(on (update)
... ;; do every frame
)
(on (end)
... ;; do when state exited
)
)
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Event Handler Blocks
(define-state-script ("kickable-gate")
(state ("locked")
(on (event "kick")
... ;; handle "kick" event
• Each state contains zero or more )
(on (begin)
event handler blocks ... ;; do when state entered
)
(on (update)
... ;; do every frame
)
(on (end)
... ;; do when state exited
)
)
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Event Handler Blocks
(define-state-script ("kickable-gate")
(state ("locked")
(on (event "kick")
... ;; handle "kick" event
• Each state contains zero or more )
(on (begin)
event handler blocks ... ;; do when state entered
)
(on (update)
... ;; do every frame
)
(on (end)
... ;; do when state exited
)
)
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Runtime Script Code
• Runtime script code inside (on ...) (state ("locked")
(on (begin)
blocks [print-string "Starting idle!"]
[animate "self" "locked-idle"]
• Simplified Scheme/Lisp )
(on (event "kicked")
 Most “commands” are native calls [when [lock-broken?]
into C++ code [print-string "BAM!"]
]
 Conditional expressions [if [task-complete? "wave2"]
[print-string "Complete!"]
 Simple looping via label/goto [print-string "NOT!!!"]
]
)
)
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Runtime Script Code
• Runtime script code inside (on ...) (state ("locked")
(on (begin)
blocks [print-string "Starting idle!"]
[animate "self" "locked-idle"]
• Simplified Scheme/Lisp )
(on (event "kicked")
 Most “commands” are native calls [when [lock-broken?]
into C++ code [print-string "BAM!"]
]
 Conditional expressions [if [task-complete? "wave2"]
[print-string "Complete!"]
 Simple looping via label/goto [print-string "NOT!!!"]
]
)
)
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Monday, April 6, 2009

Runtime Script Code
• Runtime script code inside (on ...) (state ("locked")
(on (begin)
blocks [print-string "Starting idle!"]
[animate "self" "locked-idle"]
• Simplified Scheme/Lisp )
(on (event "kicked")
 Most “commands” are native calls [when [lock-broken?]
into C++ code [print-string "BAM!"]
]
 Conditional expressions [if [task-complete? "wave2"]
[print-string "Complete!"]
 Simple looping via label/goto [print-string "NOT!!!"]
]
)
)
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Monday, April 6, 2009

Runtime Script Code
• Runtime script code inside (on ...) (state ("locked")
(on (begin)
blocks [print-string "Starting idle!"]
[animate "self" "locked-idle"]
• Simplified Scheme/Lisp )
(on (event "kicked")
 Most “commands” are native calls [when [lock-broken?]
into C++ code [print-string "BAM!"]
]
 Conditional expressions [if [task-complete? "wave2"]
[print-string "Complete!"]
 Simple looping via label/goto [print-string "NOT!!!"]
]
)
)
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User-Defined Functions
(defun verbose-anim ((anim string))
[print-string "Starting " anim]
[animate "self" anim]
)
• Script functions can be defined
and called by script programmer (define-state-script ("kickable-gate")
(state ("locked")
(on (begin)
[verbose-anim "locked-idle"]
)
)
...
)
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User-Defined Functions
(defun verbose-anim ((anim string))
[print-string "Starting " anim]
[animate "self" anim]
)
• Script functions can be defined
and called by script programmer (define-state-script ("kickable-gate")
(state ("locked")
(on (begin)
[verbose-anim "locked-idle"]
)
)
...
)
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Monday, April 6, 2009

User-Defined Functions
(defun verbose-anim ((anim string))
[print-string "Starting " anim]
[animate "self" anim]
)
• Script functions can be defined
and called by script programmer (define-state-script ("kickable-gate")
(state ("locked")
(on (begin)
[verbose-anim "locked-idle"]
)
)
...
)
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Monday, April 6, 2009

User-Defined Functions
(defun verbose-anim ((anim string))
[print-string "Starting " anim]
[animate "self" anim]
)
• Script functions can be defined
and called by script programmer (define-state-script ("kickable-gate")
(state ("locked")
(on (begin)
[verbose-anim "locked-idle"]
)
)
...
)
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Monday, April 6, 2009

User-Defined Functions
(defun verbose-anim ((anim string))
[print-string "Starting " anim]
[animate "self" anim]
)
• Script functions can be defined
and called by script programmer (define-state-script ("kickable-gate")
(state ("locked")
(on (begin)
[verbose-anim "locked-idle"]
)
)
...
)
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The “Self” Argument
• Any command operating on a game object takes its unique id
(UID) as its first argument
• Magic UID "self" refers to the object to which script is attached
gate‐17
Game
Object
State Script 1
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The “Self” Argument
• Any command operating on a game object takes its unique id
(UID) as its first argument
• Magic UID "self" refers to the object to which script is attached
(on (begin)
gate‐17
[animate "self" "locked-idle"]
Game )
Object
State Script 1
self
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The “Self” Argument
• Any command operating on a game object takes its unique id
(UID) as its first argument
• Magic UID "self" refers to the object to which script is attached
gate‐17 (on (begin)
Game [animate "gate-17" "locked-idle"]
Object )
State Script 1
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Monday, April 6, 2009

The “Self” Argument
• Any command operating on a game object takes its unique id
(UID) as its first argument
• Magic UID "self" refers to the object to which script is attached
gate‐17
(on (begin)
Game [animate "lock-6" "fall-off"]
Object )
State Script 1 lock‐6
Game
Object
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Changing States
(define-state-script ("kickable-gate")
(state ("locked")
• Transitions to other states via ...
(go "state-name") command (on (event "kicked")
[when [lock-broken?]
• State transitions cause current ]
[go "opening"]
state’s (on ...) blocks to be )
)
aborted (state ("opening")
(on (begin)
• Use (on (exit) ...) block for ...
clean-up )
...
)
)
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Changing States
(define-state-script ("kickable-gate")
(state ("locked")
• Transitions to other states via ...
(go "state-name") command (on (event "kicked")
[when [lock-broken?]
• State transitions cause current ]
[go "opening"]
state’s (on ...) blocks to be )
)
aborted (state ("opening")
(on (begin)
• Use (on (exit) ...) block for ...
clean-up )
...
)
)
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Monday, April 6, 2009

Changing States
(define-state-script ("kickable-gate")
(state ("locked")
• Transitions to other states via ...
(go "state-name") command (on (event "kicked")
[when [lock-broken?]
• State transitions cause current ]
[go "opening"]
state’s (on ...) blocks to be )
)
aborted (state ("opening")
(on (begin)
• Use (on (exit) ...) block for ...
clean-up )
...
)
)
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Tracks
• (on ...) blocks contain one or more tracks
• A track is a bit like a thread or fiber
• Tracks can be put to sleep
 Wait for duration
• e.g., wait 5 seconds,
• wait until frame 23, ...
 Wait for an action to be done
• duration-agnostic
• Tracks can be synchronized via signals
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Tracks
(state ("shake-hands") State "shake‐hands"
(on (begin) On Begin
(track ("player"))
[wait-move-to "player" "waypoint7"] Track Track
P S
[signal "player-at-waypoint"]
[wait-for-signal "sully-at-waypoint"]
[wait-animate "player" "shake-sullys-hand"] s‐a‐w
)
(track ("sullivan"))
[wait-move-to "sullivan" "waypoint7"]
[signal "sully-at-waypoint"] p‐a‐w
[wait-for-signal "player-at-waypoint"]
[wait-animate "sullivan" "shake-drakes-hand"]
)
)
)
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Tracks
(state ("shake-hands") State "shake‐hands"
(on (begin) On Begin
(track ("player"))
[wait-move-to "player" "waypoint7"] Track Track
P S
[signal "player-at-waypoint"]
[wait-for-signal "sully-at-waypoint"]
[wait-animate "player" "shake-sullys-hand"] s‐a‐w
)
(track ("sullivan"))
[wait-move-to "sullivan" "waypoint7"]
[signal "sully-at-waypoint"] p‐a‐w
[wait-for-signal "player-at-waypoint"]
[wait-animate "sullivan" "shake-drakes-hand"]
)
)
)
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Monday, April 6, 2009

Tracks
(state ("shake-hands") State "shake‐hands"
(on (begin) On Begin
(track ("player"))
[wait-move-to "player" "waypoint7"] Track Track
P S
[signal "player-at-waypoint"]
[wait-for-signal "sully-at-waypoint"]
[wait-animate "player" "shake-sullys-hand"] s‐a‐w
)
(track ("sullivan"))
[wait-move-to "sullivan" "waypoint7"]
[signal "sully-at-waypoint"] p‐a‐w
[wait-for-signal "player-at-waypoint"]
[wait-animate "sullivan" "shake-drakes-hand"]
)
)
)
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Tracks
(state ("shake-hands") State "shake‐hands"
(on (begin) On Begin
(track ("player"))
[wait-move-to "player" "waypoint7"] Track Track
P S
[signal "player-at-waypoint"]
[wait-for-signal "sully-at-waypoint"]
[wait-animate "player" "shake-sullys-hand"] s‐a‐w
)
(track ("sullivan"))
[wait-move-to "sullivan" "waypoint7"]
[signal "sully-at-waypoint"] p‐a‐w
[wait-for-signal "player-at-waypoint"]
[wait-animate "sullivan" "shake-drakes-hand"]
)
)
)
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Monday, April 6, 2009

Tracks
(state ("shake-hands") State "shake‐hands"
(on (begin) On Begin
(track ("player"))
[wait-move-to "player" "waypoint7"] Track Track
P S
[signal "player-at-waypoint"]
[wait-for-signal "sully-at-waypoint"]
[wait-animate "player" "shake-sullys-hand"] p‐a‐w
)
(track ("sullivan"))
[wait-move-to "sullivan" "waypoint7"]
[signal "sully-at-waypoint"] s‐a‐w
[wait-for-signal "player-at-waypoint"]
[wait-animate "sullivan" "shake-drakes-hand"]
)
)
)
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Track Execution Over Time
• Rules for execution of code within a track:
 Greedily consume instructions sequentially...
 ... until a [wait* ...] command encountered...
 ... then relinquish control until the action is complete
• NOTE: A [wait* ...] command doesn’t have to wait; for example:
 [wait-seconds 0]
 [wait-npc-move-to "pos-4"] when she’s already there
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Options and Variable Declarations
• Options declared at top of
(define-state-script ("kickable-gate") script:
:initial-state "closed"
:declarations (decl-list
 initial state
(var "num-attempts" :type int32)
(var "is-locked" :type boolean :default #t)
 variable declarations
)  debugging options
(state ("kicked")
...
)
...
)
Game Developers Conference 2009 32
Monday, April 6, 2009

Options and Variable Declarations
• Options declared at top of
(define-state-script ("kickable-gate") script:
:initial-state "closed"
:declarations (decl-list
 initial state
(var "num-attempts" :type int32)
(var "is-locked" :type boolean :default #t)
 variable declarations
)  debugging options
(state ("kicked")
...
)
...
)
Game Developers Conference 2009 32
Monday, April 6, 2009

Options and Variable Declarations
• Options declared at top of
(define-state-script ("kickable-gate") script:
:initial-state "closed"
:declarations (decl-list
 initial state
(var "num-attempts" :type int32)
(var "is-locked" :type boolean :default #t)
 variable declarations
)  debugging options
(state ("kicked")
...
)
...
)
Game Developers Conference 2009 32
Monday, April 6, 2009

(define-state-script ("kickable-gate")
:initial-state "closed"
Manipulating Variables :declarations (decl-list
(var "num-attempts" :type int32)
• Simple commands for reading (var "is-locked" :type boolean :default #t)
)
and writing variables (state ("kicked")
(on (begin)
• Lisp/Scheme uses prefix notation [when [get-boolean "is-locked"]
[set-int32 "num-attempts"
(a.k.a. Polish notation) [+ 1 [get-int32 "num-attempts"]]
]
 [+ a b] calculates (a + b) [wait-animate "self" "kick-failure"]
[go "closed"]
 [set "x" [+ 1 [get "x"]]] ]
increments variable “x” ;; else...
[wait-animate "self" "kick-success"]
[go "open"]
)
)
...
Game Developers Conference 2009 33
Monday, April 6, 2009

(define-state-script ("kickable-gate")
:initial-state "closed"
Manipulating Variables :declarations (decl-list
(var "num-attempts" :type int32)
• Simple commands for reading (var "is-locked" :type boolean :default #t)
)
and writing variables (state ("kicked")
(on (begin)
• Lisp/Scheme uses prefix notation [when [get-boolean "is-locked"]
[set-int32 "num-attempts"
(a.k.a. Polish notation) [+ 1 [get-int32 "num-attempts"]]
]
 [+ a b] calculates (a + b) [wait-animate "self" "kick-failure"]
[go "closed"]
 [set "x" [+ 1 [get "x"]]] ]
increments variable “x” ;; else...
[wait-animate "self" "kick-success"]
[go "open"]
)
)
...
Game Developers Conference 2009 33
Monday, April 6, 2009

(define-state-script ("kickable-gate")
:initial-state "closed"
Manipulating Variables :declarations (decl-list
(var "num-attempts" :type int32)
• Simple commands for reading (var "is-locked" :type boolean :default #t)
)
and writing variables (state ("kicked")
(on (begin)
• Lisp/Scheme uses prefix notation [when [get-boolean "is-locked"]
[set-int32 "num-attempts"
(a.k.a. Polish notation) [+ 1 [get-int32 "num-attempts"]]
]
 [+ a b] calculates (a + b) [wait-animate "self" "kick-failure"]
[go "closed"]
 [set "x" [+ 1 [get "x"]]] ]
increments variable “x” ;; else...
[wait-animate "self" "kick-success"]
[go "open"]
)
)
...
Game Developers Conference 2009 33
Monday, April 6, 2009

(define-state-script ("kickable-gate")
:initial-state "closed"
Manipulating Variables :declarations (decl-list
(var "num-attempts" :type int32)
• Simple commands for reading (var "is-locked" :type boolean :default #t)
)
and writing variables (state ("kicked")
(on (begin)
• Lisp/Scheme uses prefix notation [when [get-boolean "is-locked"]
[set-int32 "num-attempts"
(a.k.a. Polish notation) [+ 1 [get-int32 "num-attempts"]]
˘
]
 [+ a b] calculates (a + b) [wait-animate "self" "kick-failure"]
[go "closed"]
 [set "x" [+ 1 [get "x"]]] ]
increments variable “x” ;; else...
[wait-animate "self" "kick-success"]
[go "open"]
)
)
...
Game Developers Conference 2009 33
Monday, April 6, 2009

(define-state-script ("kickable-gate")
:initial-state "closed"
Manipulating Variables :declarations (decl-list
(var "num-attempts" :type int32)
• Simple commands for reading (var "is-locked" :type boolean :default #t)
)
and writing variables (state ("kicked")
(on (begin)
• Lisp/Scheme uses prefix notation [when [get-boolean "is-locked"]
[set-int32 "num-attempts"
(a.k.a. Polish notation) [+ 1 [get-int32 "num-attempts"]]
]
 [+ a b] calculates (a + b) [wait-animate "self" "kick-failure"]
[go "closed"]
 [set "x" [+ 1 [get "x"]]] ]
increments variable “x” ;; else...
[wait-animate "self" "kick-success"]
[go "open"]
)
)
...
Game Developers Conference 2009 33
Monday, April 6, 2009

Configuration Parameters
• All game objects have
properties (key-value pairs)
 Property values edited in
Charter
Game Developers Conference 2009 34
Monday, April 6, 2009

Configuration Parameters
• All game objects have
properties (key-value pairs)
 Property values edited in
Charter
Game Developers Conference 2009 34
Monday, April 6, 2009

Configuration Parameters
• Designers can create their
own free-form properties,
called tags meaning-of-life = 42
 Simply type “key = value”
in Tags field
Game Developers Conference 2009 34
Monday, April 6, 2009

Configuration Parameters
• State scripts have read-only access to game object properties...
 ... and free-form tags
Game Developers Conference 2009 35
Monday, April 6, 2009

Configuration Parameters
• State scripts have read-only access to game object properties...
 ... and free-form tags
(define-state-script ("kickable-gate")
(state ("kicked")
(on (begin)
[wait-animate "self"
[tag-string "kick-anim"]
]
)
...
)
Game Developers Conference 2009 35
Monday, April 6, 2009

Configuration Parameters
• State scripts have read-only access to game object properties...
 ... and free-form tags
(define-state-script ("kickable-gate")
(state ("kicked")
(on (begin)
[wait-animate "self"
[tag-string "kick-anim"]
]
)
...
)
Game Developers Conference 2009 35
Monday, April 6, 2009

Configuration Parameters
• State scripts have read-only access to game object properties...
 ... and free-form tags
(define-state-script ("kickable-gate")
(state ("kicked")
(on (begin)
[wait-animate "self"
[tag-string "kick-anim"]
]
)
...
)
Game Developers Conference 2009 35
Monday, April 6, 2009

Data Definition and Runtime
(define-state-script ("kickable-gate")
• Offline data-definition language (state ("locked")
(on (begin)
(Scheme) is intermingled with [print-string "Starting idle!"]
[animate "self" "locked-idle"]
runtime code )
(on (event "kicked")
[when [lock-broken?]
[print-string "BAM!"]
]
[if [task-complete? "wave2"]
[print-string "Complete!"]
[print-string "NOT!!!"]
]
)
)
...
)
Game Developers Conference 2009 36
Monday, April 6, 2009

Data Definition and Runtime
(define-state-script ("kickable-gate")
• Offline data-definition language (state ("locked")
(on (begin)
(Scheme) is intermingled with [print-string "Starting idle!"]
[animate "self" "locked-idle"]
runtime code )
(on (event "kicked")
[when [lock-broken?]
[print-string "BAM!"]
]
[if [task-complete? "wave2"]
[print-string "Complete!"]
[print-string "NOT!!!"]
]
)
)
...
)
Game Developers Conference 2009 36
Monday, April 6, 2009

Data Definition and Runtime
class Vector3
{
private:
float x, y, z;
• Really no different than the public:
float Dot(const Vector3& b)
distinction between declarations {
return (x * b.x
and definitions in C++ + y * b.y
+ z * b.z);
}
...
};
Game Developers Conference 2009 36
Monday, April 6, 2009

Data Definition and Runtime
class Vector3
{
private:
float x, y, z;
• Really no different than the public:
float Dot(const Vector3& b)
distinction between declarations {
return (x * b.x
and definitions in C++ + y * b.y
+ z * b.z);
}
...
};
Game Developers Conference 2009 36
Monday, April 6, 2009

Case Studies
37
Monday, April 6, 2009

Custom Object Type: Breakable Sign
Game Developers Conference 2009 38
Monday, April 6, 2009

Custom Object Type: Breakable Sign
Game Developers Conference 2009 38
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(define-state-script ("falling-sign")
(state ("untouched")
(on (update)
[when [task-complete? "wz-post-combat"]
[go "fallen"]
]
)
(on (event "hanging-from")
[go "breaking"]
)
)
...
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(define-state-script ("falling-sign")
(state ("untouched")
(on (update)
[when [task-complete? "wz-post-combat"]
[go "fallen"]
]
)
(on (event "hanging-from")
[go "breaking"]
)
)
...
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(define-state-script ("falling-sign")
(state ("untouched")
(on (update)
[when [task-complete? "wz-post-combat"]
[go "fallen"]
]
)
(on (event "hanging-from")
[go "breaking"]
)
)
...
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
[spawn-particles-at-joint "self"
"hinge"
"sign-break-dust"]
[wait-animate "self" "sign-break"]
[go "fallen"]
)
)
(state ("fallen")
(on (begin)
[animate "self" "sign-broken"] ;; looping
)
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
(define-state-script ("falling-sign")
[spawn-particles-at-joint "self"
(state ("untouched")
"hinge"
(on (update)
"sign-break-dust"]
[when [task-complete? "wz-post-combat"]
[wait-animate "self" "sign-break"]
[go "fallen"]
[go "fallen"]
]
)
)
)
(on (event "hanging-from")
(state ("fallen")
[go "breaking"]
(on (begin)
)
[animate "self" "sign-broken"] ;; looping
)
)
...
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
(define-state-script ("falling-sign")
[spawn-particles-at-joint "self"
(state ("untouched")
"hinge"
(on (update)
"sign-break-dust"]
[when [task-complete? "wz-post-combat"]
[wait-animate "self" "sign-break"]
[go "fallen"]
[go "fallen"]
]
)
)
)
(on (event "hanging-from")
(state ("fallen")
[go "breaking"]
(on (begin)
)
[animate "self" "sign-broken"] ;; looping
)
)
...
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Custom Object Type: Breakable Sign
(state ("breaking")
(on (begin)
(define-state-script ("falling-sign")
[spawn-particles-at-joint "self"
(state ("untouched")
"hinge"
(on (update)
"sign-break-dust"]
[when [task-complete? "wz-post-combat"]
[wait-animate "self" "sign-break"]
[go "fallen"]
[go "fallen"]
]
)
)
)
(on (event "hanging-from")
(state ("fallen")
[go "breaking"]
(on (begin)
)
[animate "self" "sign-broken"] ;; looping
)
)
...
)
)
Game Developers Conference 2009 39
Monday, April 6, 2009

Making the Sign Script Generic
(state ("animating")
(on (begin)
[spawn-particles-at-joint "self"
(define-state-script ("simple-animating-obj")
[tag-string "particle-joint"]
(state ("initial")
[tag-string "particle-name"]]
(on (update)
[wait-animate "self"
[when [task-complete?
[tag-string "anim-name"]]
[tag-string "done-task"]]
[go "done"]
[go "done"]
)
]
)
)
(state ("done")
(on (event "hanging-from")
(on (begin)
[go "animating"]
[animate "self"
)
[tag-string "done-anim-name"]]
)
)
...
)
)
Game Developers Conference 2009 40
Monday, April 6, 2009