1. Breakout in Greenfoot Barb Ericson ericson@cc.gatech.edu
Georgia Institute of Technology
September 2010
Breakout

2. What are the objects? Open Breakout.html in Breakout-export
And play the game (use the arrow keys to move the paddle and hit the ball into the bricks)
How do you lose? How do you win?
What are the objects in the game?
Breakout

3. The Breakout Game Open Breakout-Start
There are Bricks, a Message that says we are starting with Ball 1, a Ball, and a Paddle
But if you click on act or run nothing happens
Give your students the Breakout-Start and Breakout-export folders. The complete game is in Breakout.
Breakout

4. Game Rules Use the left and right arrow keys to move the paddle
Use the paddle to hit the ball into the bricks to get rid of them
Get rid of all the bricks to win the game
The ball will bounce off most of the walls, paddle, and bricks
You get up to three balls to use
If you still have bricks after using 3 balls you lose
If a ball hits the bottom wall it is removed and a new ball is added
Use the exported applet of Breakout in Breakout-export to show them the final game working.
Breakout

5. The Paddle Class Paddle is a subclass of Actor
public class Paddle extends Actor
A paddle object has the following fields:
width – of the paddle
height – of the paddle
moveAmount – amount to move the paddle
color – of the paddle
Breakout

6. What can actors do? Double click on the Actor class
This shows the documentation (API) for the Actor class in Greenfoot
How does an actor check if it is hitting (intersection with another actor)?
How do you get the current location of the actor (x and y values)?
How do you set the current location?
How do you change the image of the actor?
All subclasses of Actor such as Paddle and Ball can do all of these as well. They inherit the public object methods.
Breakout

7. Moving the Paddle (add to act method)
Check if the left key is down and if so move the paddle left by the moveAmount
if (Greenfoot.isKeyDown("left")) {
setLocation(getX()-moveAmount, getY()); }
Check if the right key is down and if it is move the paddle to the right
The moveAmount is a field in Paddle. Greenfoot.isKeyDown is a class (static) method on the Greenfoot class.
Breakout

8. The Ball Class Ball is a subclass of Actor
public class Ball extends Actor
Each ball object has the following fields:
radius
width
color
velX (amount to move in X)
Set in the constructor
velY (amount to move in Y)
Breakout

9. The Ball's Act Method Move the ball Check if hit any actors
Set the location using the current x and y and velX and velY (amount to move in X and Y)
Check if hit any actors
If hit an actor and that actor isn't the message
Bounce off the object
Check if the object was a brick
if it was a brick remove the brick from the world and have the world check if the player won (no more bricks)
Check if at any walls
Bounce off top or side walls
If at bottom wall remove ball and create a new one
Breakout

10. Move the Ball The ball's y velocity is 2, but it is a field
velY
The ball's x velocity should be a random value between 1 and 2 or -1 to -2
set in the constructor
velX
To move the ball
setLocation(getX() + velX,
getY() + velY);
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11. Checking if hit any Actors
Get an actor (an object of the class Actor) that intersects with this one
Actor actor = this.getOneIntersectingObject(Actor.class);
If the ball did hit an actor and the actor isn't the message (object of the Message class)
if (actor != null && !(actor instanceof Message)) {
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12. Bounce the Ball off an Actor
The actor must be a paddle or a brick (if it isn't a message)
So negate velY to make it switch direction in Y
velY = -velY;
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13. If the Ball hit a Brick Check using If the ball did hit a brick
if (actor instanceof Brick) {
If the ball did hit a brick
remove the brick from the world
world.removeObject(actor);
check if won (last brick was removed)
world.checkIfWon(); }
Type in only the code which is shown in the courier font.
Breakout

14. Checking Walls If the ball hit the left wall bounce in x
if (getX() - radius <= 0)
velX = -velX; // negate velocity in X
if the ball hit the right wall bounce in x
else if (getX() + radius >=
BreakoutWorld.WIDTH)
if the ball hit the top wall bounce in y
else if (getY() - radius <= 0)
velY = -velY; // negate velocity in Y
Type in just the code (in courier font).
Breakout

15. Checking Bottom Wall remove the current ball from the world
else if (getY() + radius >= BreakoutWorld.HEIGHT) {
remove the current ball from the world
world.removeObject(this);
add a new ball to the world
world.newBall();
this also checks for the end of the game }
Breakout

16. Additional Ideas Add sounds
bounce sound and win or lose sounds
If the ball hits at the edge of paddle then bounce in x as well as y
if the distance from the center of the ball to the left or right edge of the paddle is less than or equal the radius of the ball
Speed up the velocity
after each 7th hit with the paddle
double the x velocity
Make the paddle smaller over time
Change the ball color to match the last hit brick's color
Add a getColor() method to Brick
See the documentation for the Greenfoot classes
Breakout