Question

I am trying to learn some more about vectors and rotation in Java by making a simple asteroids game. I have been trying out the Vector2d class, but I feel like I could have done it just using Points and doubles. Is my use of the Vector2d redundant? How would you change my program?

Source:

import java.awt.Color;
import java.awt.Cursor;  
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import javax.vecmath.Vector2d;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Asteroids extends JPanel implements Runnable{
    BufferedImage img;
    boolean up, left, right;
    double angle = 0;
    int imgw = 0;
    int imgh = 0;
    int magnitude = 0;
    JFrame f;
    ArrayList<Projectile> bullets;
    Vector2d rocket = new Vector2d();
    Vector2d Magnitude = new Vector2d();
    AffineTransform at = new AffineTransform();

    public Asteroids(JFrame f){
        this.f = f;
        setSize(900, 800);

        try {
            img = ImageIO.read(new File("res/rocket.png"));
        } catch (IOException e) {}

        imgw = img.getWidth();
        imgh = img.getHeight();

        bullets = new ArrayList<Projectile>();

        f.addKeyListener(new KeyAdapter() {
            public void keyPressed(KeyEvent evt) {
                switch (evt.getKeyCode()) {
                case KeyEvent.VK_UP:
                    up= true;
                    break;
                case KeyEvent.VK_LEFT:
                    left = true;
                    right = false;
                    break;
                case KeyEvent.VK_RIGHT:
                    right = true;
                    left = false;
                    break;
                }
            }
            public void keyReleased(KeyEvent evt) {
                switch (evt.getKeyCode()) {
                case KeyEvent.VK_UP:
                    up= false;
                    break;
                case KeyEvent.VK_LEFT:
                    left = false;
                    break;
                case KeyEvent.VK_RIGHT:
                    right = false;
                    break;
                case KeyEvent.VK_SPACE:
                    Vector2d dir = new Vector2d(Math.cos(angle-Math.toRadians(90)),Math.sin(angle-Math.toRadians(90)));
                    bullets.add(new Projectile(dir,rocket));
                    break;
                }
            }
        });         

        Thread t = new Thread(this);
        t.start();
    }

    public static void main(String[] Args){
        JFrame frame = new JFrame();
        BufferedImage cursorImg = new BufferedImage(16, 16, BufferedImage.TYPE_INT_ARGB);
        Cursor blankCursor = Toolkit.getDefaultToolkit().createCustomCursor(cursorImg, new Point(0, 0), "blank cursor");

        frame.getContentPane().setCursor(blankCursor);

        frame.add(new Asteroids(frame));
        frame.setVisible(true);
        frame.setSize(900,500);
    }

    public void paintComponent(Graphics g){
        super.paintComponent(g);

        Graphics2D g2 = (Graphics2D)g;
        g2.fillRect(0,0,this.getWidth(),this.getHeight());
        g2.drawImage(img,at,this);
        g2.setColor(Color.red);
        for(Projectile p: bullets){
            p.draw(g2);
        }
    }

    public void run(){
        rocket = new Vector2d(100, 400);
        Magnitude = new Vector2d(Magnitude = new Vector2d(magnitude*Math.cos(angle-Math.toRadians(90)),magnitude*Math.sin(angle-Math.toRadians(90))));

        while(true){
            if(left){
                angle-=Math.toRadians(5);
            }
            if(right){
                angle+=Math.toRadians(5);
            }
            if(up){
                Vector2d m2 = new Vector2d(Math.cos(angle-Math.toRadians(90)),Math.sin(angle-Math.toRadians(90)));
                m2.normalize();
                m2.x/=5;
                m2.y/=5;
                Magnitude.add(m2);
            }

            if(angle>=Math.toRadians(360)){
                angle-=Math.toRadians(360);
            }else if(angle<=Math.toRadians(-360)){
                angle+=Math.toRadians(360);
            }

            Vector2d rocketN = new Vector2d(rocket);
            rocketN.normalize();

            rocket.add(Magnitude);

            System.out.println(Math.toDegrees(angle));

            at.setToTranslation(rocket.x-img.getWidth()/2, rocket.y-img.getHeight()/2); 
            at.rotate(angle, imgw/2, imgh/2); 

            Magnitude.x*=0.99;
            Magnitude.y*=0.99;

            for(Projectile p: bullets){
                p.update();
            }

            repaint();

            try {Thread.sleep(25);
            } catch (InterruptedException e) {}
        }
    }

    public class Projectile{

        int magnitude;
        private Vector2d Magnitude, position;

        public Projectile(Vector2d dir, Vector2d Position){
            this.position = new Vector2d(Position);
            magnitude = 10;
            Magnitude = new Vector2d(dir);
            position.x+=(5*Magnitude.x);
            position.y+=(5*Magnitude.y);
            Magnitude.x*=magnitude;
            Magnitude.y*=magnitude;
        }

        public void update(){
            position.add(Magnitude);
        }

        public void draw(Graphics2D g2){
            g2.drawOval((int)position.x, (int)position.y,4,4);
        }
    }
}

Currently there is no asteroids to shoot, you can just move around and shoot. Here is the Image I used: http://findicons.com/files/icons/1495/space/32/rocket_ship.png

Answer 1

• I think that not (answer to your question)

• but most important is there wrong usage of KeyListener, use KeyBindings instead, example for Keys UP, DOWN, LEFT, RIGHT

• (I’m not good in Graphics2D) but another issues could be caused by method

  public void draw(Graphics2D g2){

check this thread how to move with Graphics2D, especialy answer by @trashgod