import greenfoot.*;  



| A lunar lander
|
| @author Poul Henriksen
| @author Michael Kölling
|
| @version 1.1
|
public class Lander
extends Actor
{    


| Current speed
|
private double speed = 0;
     
    

| Allowed speed for landing speed
|
private double MAX_LANDING_SPEED = 12;
    
    

| Power of the rocket
|
private double thrust = -3;
    
    

| The location
|
private double altitude;
    
    

| The speed is divided by this.
|
private double speedFactor = 10;
    
    

| Rocket image without thrust
|
private GreenfootImage rocket;
   
    

| Rocket image with thrust
|
private GreenfootImage rocketWithThrust;
    
    

| Moon we are trying to land on
|
private Moon moon;    
    
    

| Bottom of lander (offset in pixels from centre)
|
private int bottom = 15;
    
    public Lander()
    {
        rocket = getImage();
        rocketWithThrust = new GreenfootImage("thrust.png");
        rocketWithThrust.drawImage(rocket, 0, 0);
    }       

    public void act()
    {
        processKeys();
        applyGravity();
        
        altitude += speed / speedFactor;
        setLocation(getX(), (int) (altitude));
        checkCollision();
    }

    


| Lander has been added to the world.
|
public void addedToWorld(World world) 
    {
        moon = (Moon) world;        
        altitude = getY();
    }
    
    


| Handle keyboard input.
|
private void processKeys() 
    {
        if(Greenfoot.isKeyDown("down")) 
        {
            speed+=thrust;
            setImage(rocketWithThrust);
        } else {
            setImage(rocket);
        }
    }
    
    


| Let the gravity change the speed.
|
private void applyGravity() 
    {
        speed += moon.getGravity();
    }
    
    


| Whether we have touched the landing platform yet.
|
private boolean isLanding() 
    {
        Color colorBelow = moon.getColorAt(getX(), getY() + bottom);
        return (speed <= MAX_LANDING_SPEED) && !colorBelow.equals(moon.getSpaceColor());
    }
     
    


| Is the lander exploding?
|
private boolean isExploding() 
    {
        Color colorBelow = moon.getColorAt(getX(), getY() + bottom);
        return (speed > MAX_LANDING_SPEED) && !colorBelow.equals(moon.getSpaceColor());
    }
    
    


| Check if we are colliding with anything and take appropiate action.
|
private void checkCollision() 
    {
        if (isLanding()) {
            setImage(rocket);
            moon.addObject(new Flag(), getX(), getY());
            Greenfoot.stop();
        } 
        else if (isExploding()) {
            moon.addObject(new Explosion(), getX(), getY());
            moon.removeObject(this);
        }
    }
}