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

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

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

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

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

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

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

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

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

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); Breakout

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)) { Breakout

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; Breakout

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

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

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

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 http://www.greenfoot.org/doc/javadoc/ Breakout