The document discusses various techniques for detecting collisions and handling user interaction in Flash games, including: 1) hitTestObject and hitTestPoint methods to detect collisions between objects based on overlapping bounding boxes or a point touching an edge. 2) Using the Pythagorean theorem and distance formula to detect collisions based on objects being within a certain distance of each other. 3) Listening for keyboard events to handle user input, and checking the keyCode property to determine which keys are pressed. 4) Implementing movement and jumping logic that uses time-based calculations rather than frames to provide smoother animation in response to keyboard input.

1. ARTDM 170, Week 11: User Interaction Gilbert Guerrero [email_address] gilbertguerrero.com/blog/artdm-170

2. Turn in Homework Please put your files in a folder with your last name and first initial Put the folder in my dropbox Example: smith-h Memory-Game.swf

3. Collision Detection

4. hitTestObject When the bounding box of one object overlaps with the bounding box of another object, a collision is detected Use an if() statement to do something with the collision if( sprite1.hitTestObject(sprite2) ){ // collision happened } sprite1 sprite2

5. hitTestPoint Check if the edge of a shape is near a point Cannot be used with two shapes, only a shape and a point Can be used with the mouse, using mouseX and mouseY sprite1 if( sprite1.hitTestPoint(x1, y1, true) ){ // collision happened }

6. Collision based on distance Detect when two objects are near each other Collide when the distance between their registration points is less than half their combined sizes sprite1 sprite2 sprite1 sprite2

7. Pythagorean Theorem To find the distance between two points we need the Pythagorean Theorem A 2 + B 2 = C 2 A B C

8. Pythagorean Theorem In ActionScript: dx = x2 - x1; dy = y2 - y1; dist = Math.sqrt(dx*dx + dy*dy); (x1,y1) dist (x2,y2) (x1,y2) dx dy

9. Collision based on distance var sizeBetween = sprite1.width/2 + sprite2.width/2; if(dist < sizeBetween) { // collision detected } sprite1 sprite2

10. Point.distance There’s a function for this! var sizeBetween = sprite1.width/2 + sprite2.width/2; if( Point.distance ( new Point (sprite1.x, sprite1.y), new Point (sprite2.x, sprite2.y) ) < sizeBetween ) { // collision detected } You must import the flash.geom.Point class at the top of your ActionScript after the package declaration.

11. Hit the Brick example

12. Pop the Balloon example

13. User Interaction keys and spacebar

14. Listen for Keyboard stage.addEventListener( KeyboardEvent.KEY_DOWN, keyDownFunction); stage.addEventListener( KeyboardEvent.KEY_UP, keyUpFunction);

15. Checking which key // key pressed down public function keyDownFunction(event:KeyboardEvent) { if( event.keyCode == 37 ) { leftArrow = true; } else if( event.keyCode == 39 ) { rightArrow = true; } else if( event.keyCode == 32 ) { jumpUp = true; } }

16. Checking which key // key lifted up public function keyUpFunction(event:KeyboardEvent){ if( event.keyCode == 37 ){ leftArrow = false; }else if( event.keyCode == 39 ){ rightArrow = false; } }

17. Key codes Spacebar 32 Left arrow 37 Up arrow 38 Right arrow 39 Down arrow 40 More key codes and constants on Adobe’s site

18. Moving an object // move to the left if (leftArrow) { myBrick.x -= speed ; } This would allow the user to move the object to the left at a certain speed every frame .

19. Time-based animation Using time is more accurate than frames We can capture how much time has passed and multiply it by the speed var timePassed:int = getTimer() - lastTime; lastTime += timePassed; if (leftArrow) { myBrick.x -= speed*timePassed/1000 ; }

20. Jumping script if( jumpUp ) { jumpVelocity = jumpVelocity - gravity*timePassed/1000; myBrick.y -= jumpVelocity; if( myBrick.y >= oldBrickY ) { jumpVelocity = 40; myBrick.y = oldBrickY; jumpUp = false; } }

21. Homework, due Nov 4 Create the Start and Game Over screens in Flash for your final project Make an encapsulated movie Start screen must have a start button that takes the user to the second frame Second frame must have some trigger that takes the user to the Game Over screen