New Presentation: AsteroidsPt1

• We’ll recreate the Asteroids arcade game over the next three assignments

1

Designing an Asteroids game

• What objects do we need to model?
• What do they have in common?

2

Designing an Floater class

• A super or base class for all objects that float in space
• Once we have a Floater class, we can extend it to make other sub or derived classes
1. spaceships
2. asteroids
3. bullets
4. UFOs (optional)

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3

Designing an Floater class

• What do all objects that float in space do?

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4

Designing an Floater class

• What do all objects that float in space do?
1. Move
2. Turn (Rotate)
3. Get drawn or show

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5

Designing an Floater class

• What do all objects that float in space do?
1. Move
2. Turn (Rotate)
3. Get drawn or show
• What do all objects that float in space have?

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6

Designing an Floater class

• What do all objects that float in space do?
1. Move
2. Turn (Rotate)
3. Get drawn or show
• What do all objects that float in space have?
• A number of corners
• X and Y position
• One direction (that they point)
• And a different direction (that they move)

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A sample Spaceship program

• You may find this program helpful in understanding how the Floater class works
• apcslowell.github.io/AsteroidsVariableDemoV2/

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The 9 protected member variables in Floater

protected double myCenterX, myCenterY;

//holds center coordinates

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protected double myXspeed, myYspeed;

//holds the speed of travel

//in the x and y directions

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protected double myPointDirection;

//holds current direction the floater is pointing

//in degrees

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protected member variables in Floater

protected int corners;

//the number of corners, a triangular

//floater has 3

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protected int[] xCorners;

protected int[] yCorners;

//The coordinates of the corners, with center of

//object at (0,0) and myPointDirection=0 (right)

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protected int myColor;

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extending the Floater class

• What functions would you need to write to extend Floater?

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extending the Floater class

• What functions would you need to write to extend Floater?
• You would write a constructor
• You would also write “getter” and “setter” functions as necessary

12

Constructing a Spaceship

• Initialize the 9 inherited protected variables: corners, xCorners, yCorners, myColor, myCenterX, myCenterY, myXspeed, myYspeed and myPointDirection

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(16,0)

(-8,-8)

(-8,8)

Constructing a slightly fancier Spaceship

• How would the constructor of my slightly fancier Spaceship be different?

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(16,0)

(-8,-8)

(-8,8)

(-2,0)

Constructing a slightly fancier Spaceship

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(16,0)

(-8,-8)

(-8,8)

(-2,0)

A different way

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(16,0)

(-8,-8)

(-8,8)

(-2,0)

Important: half of your coordinates should be negative!

• The Floater class was written with the assumption that (0,0) is the center of rotation and the ship is pointing to the RIGHT (0 °)
• I recommend sketching your design on graph paper

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(16,0)

(-8,-8)

(-8,8)

(-2,0)

Spaceship design worksheet�(optional)

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Hyperspace

• The assignment requires a hyperspace feature
• There is no requirement for any fancy visual effects, hyperspace just needs to stop the ship, and give it a new random position and direction

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Spaceship bob = new Spaceship();

//other code (setup, draw) not shown

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public void keyPressed(){

if(key == 'h'){

bob.??;

}

}

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Is this OK?

• Since we need to stop the ship, we’ll need to set myXspeed and myYspeed to zero

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Spaceship bob = new Spaceship();

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public void keyPressed()

{

if(key == 'h')

{

bob.myXspeed = 0;

//other Java code not shown

}

}

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NO! myXspeed is protected

• So, what is the right way to set myXspeed to zero instead of this ?

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Spaceship bob = new Spaceship();

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public void keyPressed()

{

if(key == 'h')

{

bob.myXspeed = 0;

//other Java code not shown

}

}

21

You could create a setter like setXspeed()

• Since it is a member of the Spaceship class it has access to myXspeed

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class Spaceship extends Floater

{

public SpaceShip() {

//construtor code not shown

}

public void setXspeed(double x) {

myXspeed = x;

}

//other functions not shown

}

22

Or you could create a hyperspace()

class Spaceship extends Floater

{

public SpaceShip() {

//construtor code not shown

}

public void hyperspace() {

//code not shown

}

//other functions not shown

}

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Either way is fine

• Then use the setter function setXspeed() in keyPressed

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Spaceship bob = new Spaceship();

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public void keyPressed()

{

if(key == 'h')

{

bob.setXspeed(0); //OK!

//or

bob.hyperspace(); //OK!

//other Java code not shown

}

}

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Asteroids Pt 1: Star class

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• Your program should have a Star class that creates the background of the game

If you wrote this Star class on the AP, they would deduct points. Why?

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Like every class on the AP exam the Star class needs to be encapsulated

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Creating an Array of Stars

• There is a common mistake in this code, do you see it?

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Creating an Array of Stars

• Every time we draw the screen we are creating 200 new Stars in new positions

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This is what creating new Stars in new positions everytime you draw the screen looks like

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Creating an Array of Stars

• A better idea would be to create 200 new Stars once in setup() using an Array

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Creating an Array of Stars

• Then we would show() the same 200 Stars everytime we draw() the screen

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Adding instructions in index.html

• A requirement for this assignment is to put the instructions on how to control the spaceship in the webpage
• One place would be the footer of index.html

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Adding instructions in the html

• <br> is the html code (called a tag) to insert a line break

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