1. SM1205 Interactivity Topic 04: Properties and Events Spring 2010SCM-CityU1

2. Today’s Example Pingpong-like game Spring 2010SCM-CityU2

3. Review: Functions Example: math function f(x, y) = x 2 +y 2 Spring 2010SCM-CityU3 trace(f(1, 2)); trace(f(2, 3)); trace(f(3, 4)); trace(f(4, 5)); function f(x:Number, y:Number): Number { return x*x + y*y; } trace(f(1, 2)); trace(f(2, 3)); trace(f(3, 4)); trace(f(4, 5)); function f(x:Number, y:Number): Number { return x*x + y*y; } function definition function calls

4. Review: Functions Position of function definition doesn’t influence program flow Spring 2010SCM-CityU4 trace(f(1, 2)); trace(f(2, 3)); trace(f(3, 4)); trace(f(4, 5)); function f(x:Number, y:Number): Number { return x*x + y*y; } trace(f(1, 2)); trace(f(2, 3)); trace(f(3, 4)); trace(f(4, 5)); function f(x:Number, y:Number): Number { return x*x + y*y; } function f(x:Number, y:Number): Number { return x*x + y*y; } trace(f(1, 2)); trace(f(2, 3)); trace(f(3, 4)); trace(f(4, 5)); function f(x:Number, y:Number): Number { return x*x + y*y; } trace(f(1, 2)); trace(f(2, 3)); trace(f(3, 4)); trace(f(4, 5)); trace(f(1, 2)); trace(f(2, 3)); function f(x:Number, y:Number): Number { return x*x + y*y; } trace(f(3, 4)); trace(f(4, 5)); trace(f(1, 2)); trace(f(2, 3)); function f(x:Number, y:Number): Number { return x*x + y*y; } trace(f(3, 4)); trace(f(4, 5));

5. Review: Statements and Blocks Simple statements are expressions followed by a semicolon (;) Spring 2010SCM-CityU5 // the following code contains four simple statements var a:int = 3; trace(a); a += 5; trace(a); // the following code contains four simple statements var a:int = 3; trace(a); a += 5; trace(a);

6. Review: Statements and Blocks Braces { and } group multiple simple statements into a compound statement or block – { and } must be matched – Indentation highly recommended – Blocks can be nested Spring 2010SCM-CityU6 function genderTest(male:Boolean): void { if (male) { trace("male"); trace("playing games"); } else { trace("female"); trace("going shopping"); } genderTest(false); function genderTest(male:Boolean): void { if (male) { trace("male"); trace("playing games"); } else { trace("female"); trace("going shopping"); } genderTest(false); Question 1: How many blocks? Question 2: Output?

7. Review: Indent Style Spring 2010SCM-CityU7 var a:Boolean = true; var b:Boolean = false; if (a) { if (b) { trace(10); } trace(5); } else { trace(20); } var a:Boolean = true; var b:Boolean = false; if (a) { if (b) { trace(10); } trace(5); } else { trace(20); } Auto Format var a:Boolean = true; var b:Boolean = false; if (a) { if (b) { trace(10); } trace(5); } else { trace(20); } var a:Boolean = true; var b:Boolean = false; if (a) { if (b) { trace(10); } trace(5); } else { trace(20); }

8. Review: Indent Style Indentation reveals program structure easily Spring 2010SCM-CityU8 var a:Boolean = true; var b:Boolean = false; if (a) { if (b) { trace(10); } else { trace(20); } trace(5); } var a:Boolean = true; var b:Boolean = false; if (a) { if (b) { trace(10); } else { trace(20); } trace(5); } var a:Boolean = true; var b:Boolean = false; if (a) { if (b) { trace(10); } else { trace(20); } trace(5); } var a:Boolean = true; var b:Boolean = false; if (a) { if (b) { trace(10); } else { trace(20); } trace(5); }

9. Properties Symbol instances provide a lot of properties for manipulation, e.g., – x, y – width, height – scaleX, scaleY – alpha – visible Access properties using dot syntax – E.g., ball.rotation += 30; Spring 2010SCM-CityU9

10. Properties Why bother property changing in ActionScript? – To support interactivity! But you can use properties panel to set initial properties Spring 2010SCM-CityU10

11. Properties: x, y Using dot syntax Units: pixels Spring 2010SCM-CityU11 O X Y

12. Properties: width, height Spring 2010SCM-CityU12 O X Y box.width box.height

13. Properties: scaleX, scaleY Multiplies current width/height by a scale factor Spring 2010SCM-CityU13 O X Y box.scaleX = 0.5; box.scaleY = 0.5;

14. Properties: rotation Clockwise; angle in degree Spring 2010SCM-CityU14 O X Y

15. Properties: alpha Range: [0, 1] Spring 2010SCM-CityU15 box.alpha = 1; box.alpha = 0.5;

16. Class Exercise Create a symbol instance similar to the one below and change its properties in ActionScript – Fill shape with gradient color using Paint Bucket Tool Spring 2010SCM-CityU16 Instance name: ball

17. Events & Listeners Multiple parties might be interested in special things, called events (e.g., clicking), happened to a target object (e.g., a button) Spring 2010SCM-CityU17 Hi folks, I have been clicked!

18. Spring 2010SCM-CityU18 Hi folks, I have been clicked! Got it. I will perform some follow-up task Who cares! I’m only interested in keyboard events on you

19. Events & Listeners In ActionScript, eventTarget.addEventListener ( EventType, eventListener); – btn.addEventListener(MouseEvent.CLICK, clickTask); – btn.addEventListener(KeyboardEvent.KEY_DOWN, keyDownTask); Spring 2010SCM-CityU19 Hi folks, I have been clicked! Got it. I will perform some follow-up task Who cares. I’m only interested in keyboard events on you

20. eventTarget can be – Any symbol instance you create, e.g., a button! – Stage, timer (to be covered soon), Spring 2010SCM-CityU20 btn_prev.addEventListener(MouseEvent.CLICK, onPrevButtonClick); function onPrevButtonClick(e:MouseEvent) : void { prevFrame(); txt_index.text = currentFrame + "/" + totalFrames; } btn_prev.addEventListener(MouseEvent.CLICK, onPrevButtonClick); function onPrevButtonClick(e:MouseEvent) : void { prevFrame(); txt_index.text = currentFrame + "/" + totalFrames; } eventTarget.addEventListener (EventType, eventListener);

21. Listen to an event type you only care! There are many event types defined in Event, TimerEvent, KeyboardEvent, MouseEvent, … – E.g., MouseEvent.CLICK Spring 2010SCM-CityU21 btn_prev.addEventListener( MouseEvent.CLICK, onPrevButtonClick); function onPrevButtonClick(e:MouseEvent) : void { prevFrame(); txt_index.text = currentFrame + "/" + totalFrames; } btn_prev.addEventListener( MouseEvent.CLICK, onPrevButtonClick); function onPrevButtonClick(e:MouseEvent) : void { prevFrame(); txt_index.text = currentFrame + "/" + totalFrames; } eventTarget.addEventListener ( EventType, eventListener);

22. eventListener is simply a function but always with a single special parameter – Though this parameter you can get the context where the event happens Spring 2010SCM-CityU22 btn_prev.addEventListener( MouseEvent.CLICK, onPrevButtonClick ); function onPrevButtonClick ( e:MouseEvent ) : void { prevFrame(); txt_index.text = currentFrame + "/" + totalFrames; } btn_prev.addEventListener( MouseEvent.CLICK, onPrevButtonClick ); function onPrevButtonClick ( e:MouseEvent ) : void { prevFrame(); txt_index.text = currentFrame + "/" + totalFrames; } eventTarget.addEventListener (EventType, eventListener );

23. Execution Flow When an event happens to a target, all registered listeners that are listening to this event type are invoked E.g., when click event happens to btn – clickTask function will be called – But keyDownTask function won’t Spring 2010SCM-CityU23 btn.addEventListener(MouseEvent.CLICK, clickTask); btn.addEventListener(KeyboardEvent.KEY_DOWN, keyDownTask); btn.addEventListener(MouseEvent.CLICK, clickTask); btn.addEventListener(KeyboardEvent.KEY_DOWN, keyDownTask);

24. Timer Event Timer is a complex data type in ActionScript – Useful for create animation, since it can dispatch some timer event for every short period Spring 2010SCM-CityU24 I will give you a TimerEvent for every second. Great. I will update the ball position for every second.

25. Timer Event For complex data types, variable definition is a bit different – var varName:ComplexType = new ComplexType(para1,…,para2); – E.g. var timer:Timer = new Timer(20); First parameter specifies how often a timer event should happen In milliseconds (0.02 second for the above example) Spring 2010SCM-CityU25

26. Timer Event Timer instance will not start to invoke events until you call its start method – Timer is a complex data type, so it can have some functions associated with it – Those associated functions are called methods Spring 2010SCM-CityU26 var timer:Timer = new Timer(20); // for 0.02 second timer.start(); var timer:Timer = new Timer(20); // for 0.02 second timer.start();

27. Timer Event Now it’s time to add an event listener for handling timer event – We listen to only event type: TimerEvent.TIMER Spring 2010SCM-CityU27 var timer:Timer = new Timer(20); // for 0.02 second timer.start(); timer.addEventListener(TimerEvent.TIMER, onTimer); function onTimer(evt:TimerEvent):void { ball.rotation += 5; } var timer:Timer = new Timer(20); // for 0.02 second timer.start(); timer.addEventListener(TimerEvent.TIMER, onTimer); function onTimer(evt:TimerEvent):void { ball.rotation += 5; }

28. Let’s Make Ball Moving Spring 2010SCM-CityU28 O X Y ball.x += ball_speed_x; ball.y += ball_speed_y;

29. Bouncing Against Boundary Spring 2010SCM-CityU29 O X Y How ?

30. Bouncing Against Boundary If ball.y is too large (i.e., > stage.stageHeight) – Set ball.y = stage.stageHeight; – And set ball_speed_y *= -1; // moving along negative y axis Class Exercise Spring 2010SCM-CityU30 O X Y y = stage.stageHeight... if (conditionA) { // process B }... if (conditionA) { // process B }... x = stage.stageWidth +y-y

31. O X Y Bouncing Against Boundary Since ball has its radius (i.e., r = ball.width / 2), it should bounce at y = stage.stageHeight - r; // for bottom border Class Exercise – Update and fix Spring 2010SCM-CityU31 y = stage.stageHeight - r

32. Bouncing Against Catcher Next step: add user interaction – User controls a horizontal bar, called catcher Spring 2010SCM-CityU32 Instance name: catcher

33. Keyboard Event Making the catcher move horizontally by pressing left or right key – stage is a variable you can always access Spring 2010SCM-CityU33 stage Hi buddy, some key has been pressed OK. Let me check if left or right key has been pressed

34. Keyboard Event KeyboardEvent provides event types for key down or up The info that be passed from stage to listener includes the key being pressed (keyCode) Spring 2010SCM-CityU34 stage.addEventListener(KeyboardEvent.KEY_DOWN, onBarControl); function onBarControl(e:KeyboardEvent):void { if ( e.keyCode==Keyboard.LEFT ) { trace("Left key pressed"); } stage.addEventListener(KeyboardEvent.KEY_DOWN, onBarControl); function onBarControl(e:KeyboardEvent):void { if ( e.keyCode==Keyboard.LEFT ) { trace("Left key pressed"); }

35. Class Exercise Change x property of catcher when left or right key is pressed – catcher.x -= catcher_speed; // for left key – catcher.x += catcher_speed; // for right key Catcher movement should stop if it hits the stage border – cather.x < catcher.width / 2; // for left border Spring 2010SCM-CityU35

36. When Ball Hits Catcher This is true only if – ball.y > catcher.y – r AND – ball.x > catcher.x – catcher.width / 2 AND – ball.x < catcher.x + catcher.width / 2 Class Exercise – Add code in onTimer Spring 2010SCM-CityU36

37. Game Over When catcher fails to get the ball, the game is over – I.e., ball.y > stage.stageHeight – r is true Spring 2010SCM-CityU37

38. Game Over Idea: if game over is detected, go to the second key frame Let’s insert a key frame first Test movie! Spring 2010SCM-CityU38

39. Errors You will get errors: – TypeError: Error #1009: Cannot access a property or method of a null object reference. at PingPong_Try4_fla::MainTimeline/onTimer() at flash.utils::Timer/_timerDispatch() at flash.utils::Timer/tick() Why? Spring 2010SCM-CityU39

40. Remove Event Listeners Try to add the following code at the beginning of AS code for Frame 1 Does it help? Unfortunately, no Because at Frame 2, event listeners at Frame 1 will still keep running – But all symbol instances at Frame 1 become invalid at Frame 2 Spring 2010SCM-CityU40 stop(); // stop movieclip animation gotoAndStop(2); // go to second frame stop(); // stop movieclip animation gotoAndStop(2); // go to second frame

41. Remove Event Listeners We need to remove unused event listeners at Frame 1 before jump to Frame 2 Removing event listeners is very simple. Just replace addEventListener with removeEventListener Spring 2010SCM-CityU41 timer.removeEventListener( TimerEvent.TIMER, onTimer); stage.removeEventListener( KeyboardEvent.KEY_DOWN, onBarControl); timer.removeEventListener( TimerEvent.TIMER, onTimer); stage.removeEventListener( KeyboardEvent.KEY_DOWN, onBarControl);

42. Remove Event Listeners One remaining issue Spring 2010SCM-CityU42 function onTimer(evt:TimerEvent):void {... if (ball.y > stage.stageHeight-r) { trace("game over"); timer.removeEventListener(TimerEvent.TIMER, onTimer); stage.removeEventListener(KeyboardEvent.KEY_DOWN, onBarControl); gotoAndStop(2); } // Remaining code possibly accesses symbol instances // However, those instances cannot be accessed at frame 2... } function onTimer(evt:TimerEvent):void {... if (ball.y > stage.stageHeight-r) { trace("game over"); timer.removeEventListener(TimerEvent.TIMER, onTimer); stage.removeEventListener(KeyboardEvent.KEY_DOWN, onBarControl); gotoAndStop(2); } // Remaining code possibly accesses symbol instances // However, those instances cannot be accessed at frame 2... }

43. Function Return Spring 2010SCM-CityU43 function onTimer(evt:TimerEvent):void {... if (ball.y > stage.stageHeight-r) { trace("game over"); timer.removeEventListener(TimerEvent.TIMER, onTimer); stage.removeEventListener(KeyboardEvent.KEY_DOWN, onBarControl); gotoAndStop(2); return; // directly exit the function } // Remaining code possibly accesses symbol instances // However, those instances cannot be accessed at frame 2... } function onTimer(evt:TimerEvent):void {... if (ball.y > stage.stageHeight-r) { trace("game over"); timer.removeEventListener(TimerEvent.TIMER, onTimer); stage.removeEventListener(KeyboardEvent.KEY_DOWN, onBarControl); gotoAndStop(2); return; // directly exit the function } // Remaining code possibly accesses symbol instances // However, those instances cannot be accessed at frame 2... }

44. Function Return After calling “return”, it would directly exit the function and – Set the output as the returned value or void Spring 2010SCM-CityU44 function returnTest(): void { return; trace("this line will never execute"); } function returnTest2(): int { return 1; // set output = 1 and exit function return 2; } returnTest(); trace(returnTest2()); function returnTest(): void { return; trace("this line will never execute"); } function returnTest2(): int { return 1; // set output = 1 and exit function return 2; } returnTest(); trace(returnTest2());

45. Class Exercise Add some AS code at Frame 2 such that pressing any key will restart the game – I.e.g, go back to frame 1 Hints: – Add an event listener to check if there is any key down event for stage Similar to what we did at Frame 1 – gotoAndStop(1); Spring 2010SCM-CityU45

46. Assignment 1 Submission – Via ACS – Deadline: 23:59:59, Tuesday, 23 Feb, 2010 No late submission is allowed In-class presentation, 24 Feb – Each student has roughly 5 minutes for presentation Assessment – Based on implementation difficulty + creativity + presentation performance Spring 2010SCM-CityU46

47. Assignment 1 Topic: any interactive system – E.g., nonlinear storytelling More than one possible plotline and ending – E.g., a small interesting game Spring 2010SCM-CityU47

48. Assignment 1 Topic: any interactive system – E.g., nonlinear storytelling More than one possible plotline and ending – E.g., a small interesting game Spring 2010SCM-CityU48 Start End 1 End 2

49. Assignment 1 Requirements – Technical Jumping between key frames with user interaction – Reference: album demo Having at least three event listeners – No requirement for event types Use multiple else-if statements – Conditions must be related to user input – Content Your system must be meaningful – Not just simply a piece of code to satisfy technical requirements Spring 2010SCM-CityU49 if (...) { } else if (...) { } else { } if (...) { } else if (...) { } else { }

50. Assignment 1 Optional tasks – Write and use your own functions With or without parameters With or without returning values – Nested if statements Spring 2010SCM-CityU50