the gamedesigninitiative at cornell university Architecture Revisited Recall: The Game Loop Receive player input Process player actions Update 60 times/s Process NPC actions Interactions (e.g. physics) = 16.7 ms Cull non-visible objects Transform visible objects Draw Draw to backing buffer Display backing buffer The Game Loop Receive player input Process player actions Update Process NPC actions Interactions (e.g. physics) Almost everything is in loop Draw Except asynchronous actions Is enough for simple games How do we organize this loop? Do not want spaghetti code Distribute over programmers Model-View-Controller Pattern Controller Calls the • Updates model in methods of response to events • Updates view with model changes Model View • Defines/manages • Displays model the program data to the user/player • Responds to the • Provides interface controller requests for the controller The Game Loop and MVC Model: The game state Value of game resources Location of game objects Update View: The draw phase Rendering commands only Major computation in update Draw Controller: The update phase Alters the game state Vast majority of your code Structure of a CUGL Application Main Application Scene Scene Models Root Node Models Root Node Structure of a CUGL Application Main Application Memory policy (future lecture) App Configuration Scene Scene Models Root Node Models Root Node Structure of a CUGL Application Main Application Active Dormant Scene Scene Models Root Node Models Root Node Structure of a CUGL Application Main Application Controller(s) Scene Scene Models Root Node Models Root Node View The Application Class onStartup() update() Handles the game assets Called each animation frame Attaches the asset loaders Manages gameplay Loads immediate assets Converts input to actions Starts any global singletons Processes NPC behavior Example: AudioEngine Resolves physics Resolves other interactions Creates any player modes But does not launch yet Updates the scene graph Waits for assets to load Transforms nodes Like GDXRoot in 3152 Enables/disables nodes The Application Class onStartup() update() Handles the game assets Called each animation frame Attaches the asset loaders Manages gameplay Loads immediate assets Converts input to actions Starts any global singletons Processes NPC behavior () Does not draw! onShutdown Example: AudioChannels ResolvesHandled physicsseparately cleans this up Resolves other interactions Creates any player modes But does not launch yet Updates the scene graph Waits for assets to load Transforms nodes Like GDXRoot in 3152 Enables/disables nodes Application Structure Scene Controller Ownership Subcontroller Subcontroller View Model Model Model Collaboration Application Structure Scene Collaboration Controller Must import class/interface Ownership Instantiates an object OR Calls the objects methods Subcontroller Subcontroller Ownership View Instantiated the object Responsible for disposal Superset of collaboration Model Model Model Collaboration Avoid Cyclic Collaboration Controller collaborates with Z Y X collaborates with X collaborates with Y Scene Structure Scene Controller Subcontroller Subcontroller View ? Model Model Model CUGL Views: Scene Graphs Scene Root Node Model Node Node Node Node Node Node Model CUGL Views: Scene Graphs Scene Root Node Model Node Node Node Node Node Node Model CUGL Views: Scene Graphs Scene Root Node for Another Lecture TopicModel Node Node Node Node Node Node Model Model-Controller Separation (Standard) Model Controller Store/retrieve object data Process user input Limit access (getter/setter) Determine action for input Preserve any invariants Example: mouse, gamepad Only affects this object Call action in the model Implements object logic Complex actions on model Traditional controllers May affect multiple models are “lightweight” Example: attack, collide Classic Software Problem: Extensibility Given: Class with some base functionality Might be provided in the language API Might be provided in 3rd party software Goal: Object with additional functionality Classic solution is to subclass original class first Example: Extending GUI widgets (e.g. Java) But subclassing does not always work… How do you extend a Singleton object? Problem with Subclassing Games have lots of classes Each game entity is different NPC Needs its own functionality (e.g. object methods) Human Orc Want to avoid redundancies Makes code hard to change Common source of bugs Human Human Orc Orc Warrior Archer Warrior Archer Might be tempted to subclass Common behavior in parents Specific behavior in children Redundant Behavior Problem with Subclassing Games have lots of classes Each game entity is different NPC Needs its own functionality No Help (e.g. object methods) Warrior Archer Want to avoid redundancies Makes code hard to change Common source of bugs Human Orc Human Orc Warrior Warrior Archer Archer Might be tempted to subclass Common behavior in parents Specific behavior in children Redundant Behavior Model-Controller Separation (Standard) Model NPC Store/retrieve object data Limit access (getter/setter) Preserve any invariants Human Orc Only affects this object Implements object logic Human Human Orc Orc Warrior Archer Warrior Archer Complex actions on model May affect multiple models Example: attack, collide Redundant Behavior Model-Controller Separation (Alternate) Model Controller Store/retrieve object data Process game actions Limit access (getter/setter) Determine from input or AI Preserve any invariants Find all objects effected Only affects this object Apply action to objects Process interactions In this case, models Look at current game state are lightweight Look for “triggering” event Apply interaction outcome Model-Controller Separation (Alternate) Model Controller Store/retrieve object data Process game actions Limit access (getter/setter) Determine from input or AI Preserve any invariants Find all objects effected Only affects thisMotivation object for Apply the action to objects Entity-Component Process Model interactions In this case, models Look at current game state are lightweight Look for “triggering” event Apply interaction outcome Does Not Completely Solve Problem Code correctness a concern Can I Methods have specifications flee? Must use according to spec Check correctness via typing Find methods in object class Example: orc.flee() Check type of parameters Example: force_to_flee(orc) Logical association with type Even if not part of class Issues with the OO Paradigm Object-oriented programming is very noun-centric All code must be organized into classes Polymorphism determines capability via type OO became popular with traditional MVC pattern Widget libraries are nouns implementing view Data structures (e.g. CS 2110) are all nouns Controllers are not necessarily nouns, but lightweight Games, interactive media break this paradigm View is animation (process) oriented, not widget oriented Actions/capabilities only loosely connected to entities Programming and Parts of Speech Classes/Types are Nouns Actions are Verbs Methods have verb names Capability of a game object Method calls are sentences Often just a simple function subject.verb(object) damage(object) subject.verb() collide(object1,object1) Classes related by is-a Relates to objects via can-it Indicates class a subclass of Example: Orc can-it attack Example: String is-a Object Not necessarily tied to class Example: swapping items Objects are class instances Duck Typing: Reaction to This Issue “Type” determined by its Java: Names of its methods public boolean equals(Object h) { if (!(h instanceof Person)) { Names of its properties return false;} If it “quacks like a duck” Person ob= (Person)h; Python has this capability return name.equals(ob.name); } hasattr(<object>,<string>) True if object has attribute Python: or method of that name def __eq__(self,ob): if (not (hasattr(ob,'name’)) This has many problems return False Correctness is a nightmare return (self.name == ob.name) Duck Typing: Reaction to This Issue “Type” determined by its Java: Names of its methods public boolean equals(Object h) { if (!(h instanceof Person)) { Names of itsWhat properties do we really want? return false;} Capabilities over properties If it “quacks like a duck” Person ob= (Person)h; Python has this capabilityExtend capabilities withoutreturn name.equals (ob.name); necessarily changing} type hasattr(<object>,<string>) True if object hasWithout attribute using newPython: languages or method ofWe that use name software patternsdef __eq__(self,ob): if (not (hasattr(ob,'name’)) This has many problems return False Correctness is a nightmare return (self.name == ob.name) Possible Solution: Decorator Pattern New Behavior Request Decorator OriginalReference to Original Object Functionalitybase object Object Java I/O Example InputStream input = System.in; Built-in console input Reader reader = new InputStreamReader(input); Make characters easy to read BufferedReader buffer = new BufferedReader(reader); Read whole line at a time Most of java.io works this way Alternate Solution: Delegation Pattern Original Reference to Request Delegate Object delegate Object 1 Forward Request Inversion of the Decorator Pattern Alternate Solution: Delegation Pattern Original Reference to Request Delegate Object delegate Object 21 Forward Request Inversion of the Decorator Pattern Example: Sort Algorithms