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

2. 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
Game Developers Conference 2009 2
Monday, April 6, 2009

3. Introduction to State Scripts
3
Monday, April 6, 2009

4. 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
Game Developers Conference 2009 4
Monday, April 6, 2009

5. 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
Game Developers Conference 2009 5
Monday, April 6, 2009

6. 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
Game Developers Conference 2009 6
Monday, April 6, 2009

7. 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
Game Developers Conference 2009 6
Monday, April 6, 2009

8. 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
Game Developers Conference 2009 7
Monday, April 6, 2009

9. 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
Game Developers Conference 2009 8
Monday, April 6, 2009

10. 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), ...
Game Developers Conference 2009 9
Monday, April 6, 2009

11. 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...
Game Developers Conference 2009 10
Monday, April 6, 2009

12. 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)
Game Developers Conference 2009 11
Monday, April 6, 2009

13. 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 ...
Game Developers Conference 2009 12
Monday, April 6, 2009

14. 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
Game Developers Conference 2009 13
Monday, April 6, 2009

15. 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 ...
...
Game Developers Conference 2009 14
Monday, April 6, 2009

16. 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 ...
...
Game Developers Conference 2009 14
Monday, April 6, 2009

17. 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 ...
...
Game Developers Conference 2009 14
Monday, April 6, 2009

18. 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 ...
...
Game Developers Conference 2009 14
Monday, April 6, 2009

19. 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 ...
...
Game Developers Conference 2009 14
Monday, April 6, 2009

20. 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 ...
Game Developers Conference 2009 14
Monday, April 6, 2009

21. 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
Game Developers Conference 2009 14
Monday, April 6, 2009

22. Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
SsProcess
Game Developers Conference 2009 14
Monday, April 6, 2009

23. Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
SsProcess
SsInstance
Game Developers Conference 2009 14
Monday, April 6, 2009

24. Uncharted Engine’s Object Model
• Uncharted class hierarchy:
 relatively shallow, single-root
 host of add-on components
Process
ProcessGameObject
SsInstance DrawControl AnimControl ...
Game Developers Conference 2009 14
Monday, April 6, 2009

25. Charter
• World editor for
Uncharted is called
Charter
 Place game objects
 Edit object
properties
 Control level
streaming
Game Developers Conference 2009 15
Monday, April 6, 2009

26. 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
Game Developers Conference 2009 16
Monday, April 6, 2009

27. 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)
Game Developers Conference 2009 17
Monday, April 6, 2009

28. 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
Game Developers Conference 2009 18
Monday, April 6, 2009

29. 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
Game Developers Conference 2009 18
Monday, April 6, 2009

30. 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
Game Developers Conference 2009 18
Monday, April 6, 2009

31. 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
Game Developers Conference 2009 18
Monday, April 6, 2009

32. 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
Game Developers Conference 2009 19
Monday, April 6, 2009

33. 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
Game Developers Conference 2009 19
Monday, April 6, 2009

34. Instantiating State Scripts
SsProcess • Placed as stand-alone object:
State Script 3
 “director” orchestrates actions of
(stand‐alone) other objects (e.g. IGC)
Game Developers Conference 2009 20
Monday, April 6, 2009

35. 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
Game Developers Conference 2009 20
Monday, April 6, 2009

36. 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
Game Developers Conference 2009 20
Monday, April 6, 2009

37. State Script Syntax
21
Monday, April 6, 2009

38. Game Developers Conference 2009 22
Monday, April 6, 2009

39. 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")
...
)
)
Game Developers Conference 2009 23
Monday, April 6, 2009

40. 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")
...
)
)
Game Developers Conference 2009 23
Monday, April 6, 2009

41. 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")
...
)
)
Game Developers Conference 2009 23
Monday, April 6, 2009

42. 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")
...
)
)
Game Developers Conference 2009 23
Monday, April 6, 2009

43. 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
)
)
Game Developers Conference 2009 24
Monday, April 6, 2009

44. 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
)
)
Game Developers Conference 2009 24
Monday, April 6, 2009

45. 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
)
)
Game Developers Conference 2009 24
Monday, April 6, 2009

46. 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
)
)
Game Developers Conference 2009 24
Monday, April 6, 2009

47. 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
)
)
Game Developers Conference 2009 24
Monday, April 6, 2009

48. 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!!!"]
]
)
)
Game Developers Conference 2009 25
Monday, April 6, 2009

49. 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!!!"]
]
)
)
Game Developers Conference 2009 25
Monday, April 6, 2009

50. 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!!!"]
]
)
)
Game Developers Conference 2009 25
Monday, April 6, 2009

51. 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!!!"]
]
)
)
Game Developers Conference 2009 25
Monday, April 6, 2009

52. 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"]
)
)
...
)
Game Developers Conference 2009 26
Monday, April 6, 2009

53. 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"]
)
)
...
)
Game Developers Conference 2009 26
Monday, April 6, 2009

54. 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"]
)
)
...
)
Game Developers Conference 2009 26
Monday, April 6, 2009

55. 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"]
)
)
...
)
Game Developers Conference 2009 26
Monday, April 6, 2009

56. 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"]
)
)
...
)
Game Developers Conference 2009 26
Monday, April 6, 2009

57. 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
Game Developers Conference 2009 27
Monday, April 6, 2009

58. 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
Game Developers Conference 2009 27
Monday, April 6, 2009

59. 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
Game Developers Conference 2009 27
Monday, April 6, 2009

60. 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
Game Developers Conference 2009 27
Monday, April 6, 2009

61. 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 )
...
)
)
Game Developers Conference 2009 28
Monday, April 6, 2009

62. 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 )
...
)
)
Game Developers Conference 2009 28
Monday, April 6, 2009

63. 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 )
...
)
)
Game Developers Conference 2009 28
Monday, April 6, 2009

64. 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
Game Developers Conference 2009 29
Monday, April 6, 2009

65. 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"]
)
)
)
Game Developers Conference 2009 30
Monday, April 6, 2009

66. 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"]
)
)
)
Game Developers Conference 2009 30
Monday, April 6, 2009

67. 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"]
)
)
)
Game Developers Conference 2009 30
Monday, April 6, 2009

68. 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"]
)
)
)
Game Developers Conference 2009 30
Monday, April 6, 2009

69. 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"]
)
)
)
Game Developers Conference 2009 30
Monday, April 6, 2009

70. 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
Game Developers Conference 2009 31
Monday, April 6, 2009

71. 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

72. 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

73. 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

74. (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

75. (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

76. (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

77. (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

78. (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

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

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

81. 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

82. 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

83. 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

84. 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

85. 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

86. 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

87. 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

88. 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

89. 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

90. Case Studies
37
Monday, April 6, 2009

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

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

93. 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

94. 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

95. 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

96. 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

97. 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

98. 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

99. 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

100. 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

101. 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

102. 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

103. 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

104. 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

105. 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

106. 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

107. 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

108. 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