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Component Design Recall: Problem with Subclassing the gamedesigninitiative at cornell university Lecture 8 Component Design Recall: 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 Redundant Behavior Specific behavior in children the gamedesigninitiative 2 Architecture Patterns at cornell university Recall: Problem with Subclassing Games have lots of classes Each game entity is different NPC Needs its own functionality (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 Redundant Behavior Specific behavior in children the gamedesigninitiative 3 Architecture Patterns at cornell university Alternative: Decorator Pattern New Functionality OriginalReference to Original Request Decorator Object Functionalitybase object Object the gamedesigninitiative 4 Architecture Patterns at cornell university Alternate: Delegation Pattern Original Reference to Request Delegate Object delegate Object Forward Request Inversion of the Decorator Pattern the gamedesigninitiative 5 Architecture Patterns at cornell university Issues with Static Typing Method in original class Original object class obj.request(arg1,…, argn) Original Reference to Request Delegate Object delegate Object Forward Request the gamedesigninitiative 6 Architecture Patterns at cornell university The Subclass Problem Revisited Delegates? NPC Orc Slot Human Human Orc NPC Slot Slot Warrior Human Human Orc Orc Warrior Archer Warrior Archer Archer Redundant Behavior the gamedesigninitiative 7 Architecture Patterns at cornell university Component-Based Programming Delegates Role: Set of capabilities Role 1 Class with very little data A collection of methods Slot Role 2 Add it to object as delegate Entity Slot Object gains those methods Slot Role 3 Acts as a “function pointer” Role 4 Can-it: search object roles Check class of each role Field storing a Better than duck typing single delegate or " Possible at compile time? a set of delegates the gamedesigninitiative 8 Architecture Patterns at cornell university Aside: Objective-C Delegates are emphasized in Objective-C ObjC protocols function like Java interfaces But implement with a delegate, not a subclass Often leverages message passing Method call is considered a message Can call any method on any object Will get runtime error if method not supported Heavily optimized in latest Apple compilers the gamedesigninitiative 9 Architecture Patterns at cornell university Aside: Objective-C Delegates are emphasized in Objective-C ObjC protocols function like Java interfaces But implement with a delegate, not a subclass Often leverages message passing MethodAddresses call is considered Static aTyping message Issue Can call any method on any object Will get runtime error if method not supported Heavily optimized in latest Apple compilers the gamedesigninitiative 10 Architecture Patterns at cornell university Working With Static Typing Uniform Method Direct Access o.doSomething(kitchenSink) if (o has role) { extract role from o role.doSomething(info) } the gamedesigninitiative 11 Architecture Patterns at cornell university Working With Static Typing Uniform Method Direct Access o.doSomething(kitchenSink) if (o has role) { extract role from o role.doSomething(info) } Problem: Multiple capabilities the gamedesigninitiative 12 Architecture Patterns at cornell university Working With Static Typing Uniform Method Direct Access o.doSomething(kitchenSink) if (o has role) { extract role from o role.doSomething(info) } Problem: Problem: Multiple capabilities Big switch statements the gamedesigninitiative 13 Architecture Patterns at cornell university Entities Need Both Is-a and Can-it Table Chair Objects share same capabilities in theory. But certain actions are preferred on each. the gamedesigninitiative 14 Architecture Patterns at cornell university Solving the Problem Can-It Is-A Indicated by object roles Indicated by object class Component indicates role But could do more than that Check type of each role Keep a bag of types So again a typing solution Contains of the descriptions “Formal duck typing” that apply to this object Not limited to method name Example: table, heirloom Role type indicates action Why would we do this? name, not a noun the gamedesigninitiative 15 Architecture Patterns at cornell university Fast Can-It Testing: Bit Vectors Give each object a bit-vector to cover types Each role is a position in the bit vector Example: 0100101 the gamedesigninitiative 16 Architecture Patterns at cornell university Fast Can-It Testing: Bit Vectors Give each object a bit-vector to cover types Each role is a position in the bit vector Example: 0100101 Can Build Can Fight Can Heal Use array if more than 32/64 roles the gamedesigninitiative 17 Architecture Patterns at cornell university Fast Can-It Testing: Bit Vectors Give each object a bit-vector to cover types Each role is a position in the bit vector Example: 0100101 Can Build Can Fight Can Heal Use array if more than 32/64 roles Test is quick logical operation. Example: vector & CAN_FIGHT Faster than dynamic typing (why?) the gamedesigninitiative 18 Architecture Patterns at cornell university Model-Controller Separation Revisited Model Controller Store/retrieve object data Process interactions Preserve any invariants Look at current game state Data may include delegates Look for “triggering” event Determines is-a properties Apply interaction outcome Components ? Process game actions ? Attached to a entity (model) Uses the model as context the Determines can-it properties gamedesigninitiative 19 Architecture Patterns at cornell university Model-Controller Separation Revisited Model Controller Store/retrieve object data Process interactions Preserve any invariants Look at current game state Data may include delegates Look for “triggering” event Determines is-a properties Apply interaction outcome Components Is this always " the best idea? ? Process game actions ? Attached to a entity (model) Uses the model as context the Determines can-it properties gamedesigninitiative 20 Architecture Patterns at cornell university Recall: Lab 3 in CS 3152 the gamedesigninitiative 21 Architecture Patterns at cornell university Processing Actions in Lab 3 GameplayController.cs Ship.cs Decides whether to shoot Waits until objects commit Stores intent in the object Checks intent in Ship object But DOES NOT shoot Performs action for intent the gamedesigninitiative 22 Game Architecture at cornell university Processing Actions in Lab 3 GameplayController.cs Attach components " Ship.cs to controller? Decides whether to shoot Waits until objects commit Stores intent in the object Checks intent in Ship object But DOES NOT shoot Performs action for intent the gamedesigninitiative 23 Game Architecture at cornell university Related: Handling the View Way too much to draw Backgrounds UI elements Update Individual NPCs Other moveable objects Cannot cram all in Draw Draw Put it in game object? But objects are models Violates MVC again the gamedesigninitiative 24 Architecture Patterns at cornell university First Attempt: A Drawing Canvas Treat display as a container Often called a canvas Cleared at start of frame Objects added to container Draw contents at frame end Canvas abstracts rendering Passed as reference Hides animation details Like working with widget void draw(Canvas c) { // Specify perspective Implement draw(c) in model // Add to canvas" Classic heavyweight model }! No problems with extension the gamedesigninitiative 25 Architecture Patterns at cornell university Problem: Canvas Methods Ideal Model1 draw(canvas)! Canvas drawShape(…)! Model2 draw(canvas)! the gamedesigninitiative 26 Architecture Patterns at cornell university Problem: Canvas Methods In Practice Model1 draw(canvas)! Canvas drawShape1(…)! Model2 drawShape2(…)! draw(canvas)! the gamedesigninitiative 27 Architecture Patterns at cornell university Views and Components Slot Component1 Model1 Slot drawShape1(…)! Slot Canvas drawPrimitive(…)! Slot Component1 Model2 Slot drawShape1(…)! Slot the gamedesigninitiative 28 Architecture Patterns at cornell university Views and Components Primitive Slot effects Component1 Model1 Slot drawShape1(…)! Slot Complex, Shape-specific Canvas rendering drawPrimitive(…)! Slot Component1 Model2 Slot drawShape1(…)! Slot the gamedesigninitiative 29 Architecture Patterns at cornell university Components and AI NPCs use sense-think-act cycle Alert! Sense: perceive the world Think: choose an action Act: update the game state Act is stored in components Capabilities given by roles Where are sense and think? In the component/role? Yes How do roles interact? This is hard the gamedesigninitiative 30 Game Architecture at cornell university Why Do They Need to Interact? Because you are trying to pick an action NPC can only do one action (why?) Think needs all roles to pick best one Why not let each component do an action? Some things can be simultaneously (run + shoot) Only concern is conflicting actions (left vs. right) Can we guarantee components never conflict? Do we have to solve this in thinking-phase?
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