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) <ul style="display: flex;"><li style="flex:1">Human </li><li style="flex:1">Orc </li></ul>—ꢀ Want to avoid redundancies —ꢀ Makes code hard to change —ꢀ Common source of bugs Human Warrior Human Archer <ul style="display: flex;"><li style="flex:1">Orc </li><li style="flex:1">Orc </li></ul><ul style="display: flex;"><li style="flex:1">Archer </li><li style="flex:1">Warrior </li></ul>—ꢀ Might be tempted to subclass —ꢀ Common behavior in parents —ꢀ Specific behavior in children Redundant Behavior the gamedesigninitiative Architecture Patterns 2at 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) <ul style="display: flex;"><li style="flex:1">Warrior </li><li style="flex:1">Archer </li></ul>—ꢀ Want to avoid redundancies —ꢀ Makes code hard to change —ꢀ Common source of bugs Human Warrior <ul style="display: flex;"><li style="flex:1">Orc </li><li style="flex:1">Human </li></ul>Archer Orc <ul style="display: flex;"><li style="flex:1">Warrior </li><li style="flex:1">Archer </li></ul>—ꢀ Might be tempted to subclass —ꢀ Common behavior in parents —ꢀ Specific behavior in children Redundant Behavior the gamedesigninitiative Architecture Patterns 3at cornell university Alternative: Decorator Pattern New Functionality Original Object Reference to Original base object Functionality Decorator Object Request the gamedesigninitiative Architecture Patterns 4at cornell university Alternate: Delegation Pattern Original Object Reference to Delegate Request delegate Object Forward Request Inversion of the Decorator Pattern the gamedesigninitiative Architecture Patterns 5at cornell university Issues with Static Typing Method in original class Original object class obj.request(arg1,…, argn)ꢀ Original Object Reference to delegate Delegate Object Request Forward Request the gamedesigninitiative Architecture Patterns 6at cornell university The Subclass Problem Revisited Delegates? NPC Orc Slot Slot Slot Human <ul style="display: flex;"><li style="flex:1">Human </li><li style="flex:1">Orc </li></ul>NPC Warrior Archer Human Warrior Human Archer <ul style="display: flex;"><li style="flex:1">Orc </li><li style="flex:1">Orc </li></ul><ul style="display: flex;"><li style="flex:1">Archer </li><li style="flex:1">Warrior </li></ul>Redundant Behavior the gamedesigninitiative Architecture Patterns 7at 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 Slot Entity —ꢀ Object gains those methods Role 3 Role 4 Slot —ꢀ Acts as a “function pointer” —ꢀ Can-it: search object roles —ꢀ Check class of each role —ꢀ Better than duck typing —ꢀ Possible at compile time? Field storing a single delegate or a set of delegates the gamedesigninitiative Architecture Patterns 8at 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 Architecture Patterns 9at 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 Architecture Patterns 10 at cornell university Working With Static Typing <ul style="display: flex;"><li style="flex:1">Uniform Method </li><li style="flex:1">Direct Access </li></ul>ꢀif (o has role) {ꢀ o.doSomething(kitchenSink)ꢀ extract role from oꢀ role.doSomething(info)ꢀ }ꢀ the gamedesigninitiative Architecture Patterns 11 at cornell university Working With Static Typing <ul style="display: flex;"><li style="flex:1">Uniform Method </li><li style="flex:1">Direct Access </li></ul>ꢀif (o has role) {ꢀ o.doSomething(kitchenSink)ꢀ extract role from oꢀ role.doSomething(info)ꢀ }ꢀ Problem: Multiple capabilities the gamedesigninitiative Architecture Patterns 12 at cornell university Working With Static Typing <ul style="display: flex;"><li style="flex:1">Uniform Method </li><li style="flex:1">Direct Access </li></ul>ꢀif (o has role) {ꢀ o.doSomething(kitchenSink)ꢀ extract role from oꢀ role.doSomething(info)ꢀ }ꢀ Problem: Problem: Big switch statements Multiple capabilities the gamedesigninitiative Architecture Patterns 13 at cornell university Entities Need Both Is-a and Can-it ꢀ <ul style="display: flex;"><li style="flex:1">Table </li><li style="flex:1">Chair </li></ul>Objects share same capabilities in theory. But certain actions are preferred on each. the gamedesigninitiative Architecture Patterns 14 at cornell university Solving the Problem <ul style="display: flex;"><li style="flex:1">Can-It </li><li style="flex:1">Is-A </li></ul>—ꢀ Indicated by object roles —ꢀ Component indicates role —ꢀ Check type of each role —ꢀ So again a typing solution —ꢀ Indicated by object class —ꢀ But could do more than that —ꢀ Keep a bag of types —ꢀ Contains of the descriptions that apply to this object —ꢀ “Formal duck typing” —ꢀ Example: table, heirloom —ꢀ Not limited to method name —ꢀ Role type indicates action —ꢀ Why would we do this? name, not a noun the gamedesigninitiative Architecture Patterns 15 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: 0100101ꢀ the gamedesigninitiative Architecture Patterns 16 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: 0100101ꢀ Can Build <ul style="display: flex;"><li style="flex:1">Can Fight </li><li style="flex:1">Can Heal </li></ul>—ꢀ Use array if more than 32/64 roles the gamedesigninitiative Architecture Patterns 17 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: 0100101ꢀ Can Build <ul style="display: flex;"><li style="flex:1">Can Fight </li><li style="flex:1">Can Heal </li></ul>—ꢀ Use array if more than 32/64 roles —ꢀTest is quick logical operation. —ꢀ Example: vector & CAN_FIGHTꢀ —ꢀ Faster than dynamic typing (why?) the gamedesigninitiative Architecture Patterns 18 at cornell university Model-Controller Separation Revisited <ul style="display: flex;"><li style="flex:1">Model </li><li style="flex:1">Controller </li></ul>—ꢀ Store/retrieve object data —ꢀ Process interactions —ꢀ Preserve any invariants —ꢀ Data may include delegates —ꢀ Determines is-a properties —ꢀ Look at current game state —ꢀ Look for “triggering” event —ꢀ Apply interaction outcome Components <ul style="display: flex;"><li style="flex:1">?</li><li style="flex:1">?</li></ul>—ꢀ Process game actions —ꢀ Attached to a entity (model) —ꢀ Uses the model as context —ꢀ DeterAmrcihniteecsturceaPnat-tietrnps roperties the gamedesigninitiative 19 at cornell university Model-Controller Separation Revisited <ul style="display: flex;"><li style="flex:1">Model </li><li style="flex:1">Controller </li></ul>—ꢀ Store/retrieve object data —ꢀ Process interactions —ꢀ Preserve any invariants —ꢀ Data may include delegates —ꢀ Determines is-a properties —ꢀ Look at current game state —ꢀ Look for “triggering” event —ꢀ Apply interaction outcome Components Is this always the best idea? <ul style="display: flex;"><li style="flex:1">?</li><li style="flex:1">?</li></ul>—ꢀ Process game actions —ꢀ Attached to a entity (model) —ꢀ Uses the model as context —ꢀ DeterAmrcihniteecsturceaPnat-tietrnps roperties the gamedesigninitiative 20 at cornell university Recall: Lab 3 in CS 3152 the gamedesigninitiative Architecture Patterns 21 at cornell university Processing Actions in Lab 3 GameplayController.cs Ship.cs <ul style="display: flex;"><li style="flex:1">—ꢀ Decides whether to shoot </li><li style="flex:1">—ꢀ Waits until objects commit </li></ul>—ꢀ Checks intent in Ship object —ꢀ Performs action for intent —ꢀ Stores intent in the object —ꢀ But DOES NOT shoot the gamedesigninitiative Game Architecture 22 at cornell university Processing Actions in Lab 3 GameplayController.cs Attach components to controller? Ship.cs <ul style="display: flex;"><li style="flex:1">—ꢀ Decides whether to shoot </li><li style="flex:1">—ꢀ Waits until objects commit </li></ul>—ꢀ Checks intent in Ship object —ꢀ Performs action for intent —ꢀ Stores intent in the object —ꢀ But DOES NOT shoot the gamedesigninitiative Game Architecture 23 at cornell university Related: Handling the View —ꢀ Way too much to draw —ꢀ Backgrounds —ꢀ UI elements Update Draw —ꢀ Individual NPCs —ꢀ Other moveable objects —ꢀ Cannot cram all in Draw —ꢀ Put it in game object? —ꢀ But objects are models —ꢀ Violates MVC again the gamedesigninitiative Architecture Patterns 24 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 Passed as reference —ꢀ Canvas abstracts rendering —ꢀ Hides animation details void draw(Canvas c) {ꢀ // Specify perspectiveꢀ // Add to canvas }ꢀ —ꢀ Like working with widget —ꢀ Implement draw(c) in model —ꢀ Classic heavyweight model —ꢀ No problems with extension the gamedesigninitiative Architecture Patterns 25 at cornell university Problem: Canvas Methods Ideal Model1 draw(canvas)ꢀ Canvas drawShape(…)ꢀ Model2 draw(canvas)ꢀ the gamedesigninitiative Architecture Patterns 26 at cornell university Problem: Canvas Methods In Practice Model1 draw(canvas)ꢀ Canvas drawShape1(…)ꢀ drawShape2(…)ꢀ Model2 draw(canvas)ꢀ the gamedesigninitiative Architecture Patterns 27 at cornell university Views and Components Slot Component1ꢀ drawShape1(…)ꢀ Slot Slot Model1 Model2 Canvas drawPrimitive(…)ꢀ Slot Slot Slot Component1ꢀ drawShape1(…)ꢀ the gamedesigninitiative Architecture Patterns 28 at cornell university Views and Components Primitive effects Slot Component1ꢀ Slot Model1 drawShape1(…)ꢀ Slot Complex, Shape-speciﬁc rendering Slot Canvas drawPrimitive(…)ꢀ Component1ꢀ drawShape1(…)ꢀ Slot Model2 Slot the gamedesigninitiative Architecture Patterns 29 at cornell university Components and AI Alert! —ꢀ NPCs use sense-think-act cycle —ꢀ 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? Yes —ꢀ In the component/role? This is hard —ꢀ How do roles interact? the gamedesigninitiative Game Architecture 30 at cornell university

Component Design Recall: Problem with Subclassing

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