Asteroids
Games and Simulations
O-O Programming in Java
The Walker School
The Walker School – Games and Simulations - 2010
Asteroids
Take some time to play
with Asteroids. What can
the program do and what
can’t it do?
The Walker School – Games and Simulations - 2010
Discovering Keyboard Controls
Which keyboard key is
used to fire a bullet?
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Explosions
Place an explosion into a
running scenario. Does it
work? What does it do?
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Painting Stars
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Create a New Scenario
Directions
1. Create a new scenario.
2. Save it as “asteriods-lastname”.
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Create the World
Directions
1. Create a new subClass called “Space”.
2. Leave the background empty.
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Enlarge the Background
Directions:
1. Change the size of the
world (600, 400, 1).
2. Change the comment.
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Painting Backgrounds
Part IV - http://www.youtube.com/watch?v=rvZ0ErpfHKM&feature=related
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Import the Java Color Library
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Use Java to Paint Black Background
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Create a method createStars()
Comment it out until we create the method.
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Create a Method Body
Takes a parameter of type integer,
as we stated we wanted 300 stars.
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Create The Stars
Step through this loop and
explain what is happening.
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For Loops
for (initialization; loop-condition; increment)
{
loop-body;
}
•The initialization part declares and initializes a loop variable. This
variable is often called i, and often initialized to 0.
•The loop condition checks whether our loop variable is still less than a
given limit. If it is, the loop will continue.
•The increment section simply increments the loop variable.
The Walker School – Games and Simulations - 2010
Vary Star Brightness
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Rocket Firing
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Turning
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Flying Forward
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Flying Forward
Calls the move() method from SmoothMover class.
What happens?
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What Do We Need To Do?
So where are we going to do this?
• Add initial movement to the rocket.
• To add movement, we need to add force to the
rocket.
• And we need to change its vector.
• So we’ll need to call this vector from the Vector
abstract class.
• The vector needs 2 variables: direction (dy) and
length (dx).
The Walker School – Games and Simulations - 2010
Adding Drift
What happens when you change the variables in the vector?
The Walker School – Games and Simulations - 2010
What Do We Need To Do?
• Create variables to handle each rocket image.
• Add a method called ignite to checkKeys(), so
that we when hit the “up” button, the rocket
image is changed.
• Define a method called ignite. It will need a
boolean parameter and a void return type.
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Create a Method Stub to Ignite Rocket
Remember to create an instance variable called boosterOn.
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Igniting the Rocket Boosters
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Colliding with Asteroids
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What Do We Need to Do?
•
•
•
•
If we collide with an asteroid,
Remove the rocket from the world;
Place an explosion into the world;
Show final score (game over);
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Methods for Collision Detection
file:///C:/Greenfoot/doc/API/index.html
Both methods accept a parameter of type Class, which means we can
check for intersections with a specific class of objects if we want to.
Which of these 2 methods do we want to use and why?
The Walker School – Games and Simulations - 2010
Colliding with Asteroids
Remember to call the method in the rocket act() method.
The Walker School – Games and Simulations - 2010
Creating Better Explosions
•
•
•
•
•
Part I - http://www.youtube.com/watch?v=rgZ-_vQ2aIc
Part II - http://www.youtube.com/watch?v=bdv4ZgTcYyY&feature=related
Part III - http://www.youtube.com/watch?v=OFuDEt0xifM&feature=related
Part IV - http://www.youtube.com/watch?v=XMJi4_bzuLw&feature=related
Part V - http://www.youtube.com/watch?v=TKYwL8p_11A&feature=related
The Walker School – Games and Simulations - 2010
What Do We Need To Do?
• Add abstract classes SmoothMover and Vector
from Greenfoot.
• Create a constructor for Debris
• Update the move() method
Casting
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Create the Score Board
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Import Java Libraries
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Create the Assignment Variables
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Create the Constructors
Why are their 2 constructors?
How is this an example of overloading?
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Make Scoreboard Image
So, what else needs to be done?
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Activity – Change Attributes
• Modify the ScoreBoard class:
– Change the text shown on it.
– Change the color of the text.
– Change the background and frame colors.
– Change the font size so that your text fits well.
– Change the width of the scoreboard to suit your
text.
The Walker School – Games and Simulations - 2010
Homework – Scoreboard
• Search the Greenfoot library for other games
that have scoreboards. Study how they were
built. What attributes do they have that this
board does not? What could you add to your
scoreboard?
The Walker School – Games and Simulations - 2010
Add a Variable for the Counter
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Assign the Counter to the Constructor
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Call the Counter When Game Over
How can you make sure that the counter is in the
middle of the board without hard coding the
numbers?
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Ensure the Scoreboard is in the Middle
of the Background
Where do we call the gameOver() method?
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Call the Game Over Method
Example of Casting
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Casting
• Casting is the technique of telling the compiler
a more precise type for our object then it can
work out for itself. We do this by writing the
class name (Space) in parentheses before the
method call. Once we have done this we can
call methods defined in Space
• space.gameOver();
Casting does not change the type of the object returned.
The Walker School – Games and Simulations - 2010
Add a Proton Wave
What does it do?
What doesn’t it do?
The Walker School – Games and Simulations - 2010
Import the Library
We are going to need the Java List class because we are going
to create a list of images to create a proton wave that
increases in size.
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Assign Variables
How do we make the wave grow?
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Add A List (Array) to Store Image Set
How many images will this list store?
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Create a Constructer for the Wave
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Create a Method to Initialize Images
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Create a Instance Field to Set Image Count
Create a Method to Initialize Images
Rewrite the While loop using a For loop.
What needs to change?
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Create a Method Stub to Grow Wave
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Call Method to Grow the Wave
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Add Statements to Grow Wave
Square [] brackets, not curly
{} brackets here
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Add Sound to the Proton Wave
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Create a Method Stub to Ignite Proton
Wave
Where do we create this method?
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Call Method When “Z” is Pressed
What is the problem with the proton wave?
1. It can be released too easily!
2. It doesn’t do anything to the asteroids!
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Create Reload and Delay
for Wave
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Add an Instance Variable for the Delay
Where do we create these variables?
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Assign the Delay to the Constructor
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Add Delay Count to act() Method
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Program the Delay into the Wave
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Interacting with Objects in a
Range
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Program a Method Stub
to Check for Collision
Purpose is to check to see if the wave touches and asteroid.
So, in what Class do we create this method?
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Call it in the Wave act() Method
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Write Statements to
Check for Collision
Range is the radius of
the circle (wave).
Why didn’t we use the “getIntersectingObjects() method?
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hit() Method
What are the parameters for this
method and what does it return?
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Evaluating the Damage Constant
What happens when you change the damage constant of the
proton wave?
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For Further Development
• Fix the score counter.
• Add new asteroids when all have been cleared.
• Add a level counter. Every time all asteroids are
destroyed you go up a level.
• Add an end of level sound.
• Add an indicator showing the load state of the
proton wave.
• Add a shield.
The Walker School – Games and Simulations - 2010