Need help with rotation in Java

Question

Hi, I am trying to write an asteroids remake and I have gotten pretty far, but I'm stuck when I try to rotate my ship object. I have googled various formula's etc. but the code doesn't work as expected. I have posted the relevant ship.class below:
import java.awt.Polygon;
import java.awt.Graphics;
import java.awt.Shape;
import java.awt.*;
public class Ship extends MyShape {
     Polygon body;
     //line2D.Double base;
     //line2D.Double lside;
     //line2D.Double rside;
     double dx;
     double dy;
     double angle;
     double dAngle;
     Graphics2D gg;
     public Ship(double a,double b) {
    x=a;
    y=b;
    //base=new line2D.Double(x,y,x+10,y);
    //lside=new line2D.Double(x,y,x+5,y-10);
    //rside=new line2D.Double(x+10,y,x-5,y-10);
    body=new Polygon();
    body.addPoint((int)x,(int)y);
    body.addPoint((int)x+20,(int)y);
    body.addPoint((int)x+10,(int)y-30);
    public void advance(){
    public double getX(){
         return x;
    public double getY(){
         return y;
    public void setY(int y){
         this.y=y;
    public void setX(int x){
         this.x=x;
      public void move(int delta){
      body.translate(0,delta);
       // body.addPoint(x,y);
       // body.addPoint(x+20,y);
       // body.addPoint(x+10,y-30);
    public void rotate(double x, double y, double theta){
         //body=new Polygon();
         theta=theta*(Math.PI/180);
         x=((x-(x+10))*Math.cos(theta)-y*Math.sin(theta)+(x+10));
         y=(y*Math.cos(theta)+(x-(x+10))*Math.sin(theta)+y);
             //body.translate((int)Math.round(x),(int)Math.round(y));
             body.addPoint((int)Math.round(x),(int)Math.round(y));
             body.addPoint((int)Math.round(x+20),(int)Math.round(y));
             body.addPoint((int)Math.round(x+10),(int)Math.round(y-30));
             //g.rotate(theta,x,y);
    public void warpAround(int x,int y){
         body.translate(x,y);
    public void draw(Graphics2D g){
         g.draw(body);
}If you could help me I would appreciate it,
Sincerely,
LJ
P.s. I know its a little rough, I wanted to clean it up soon.
Message was edited by:
nipponman21

Answer 1

Ok, I have officially given up on trying to get it to work via the mathematical definitions of a rotational transform. I decided to use the affine transform and it was MUCH easier than I thought to implement; however, the results are still unexpected, the ship actually turns and moves in a circle which is not what I want, here is the source (its a standalone app so you can compile and run it if you want) import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
public class BouncingBall extends JFrame implements Runnable, KeyListener {
    //Windows
    private JFrame frame;
    private DrawPanel pane; 
    private Thread t;
    //Game Vars.
    public Ball ball;
    public Ship ship;
    public static final int FPS = 30;
    public static final int WIDTH = 800;
    public static final int HEIGHT = 600;
    public static final int MAXSPEED = 30;
    public static double dx,dy;
    public static int theta=0;
    public BouncingBall() {
         frame=new JFrame();
         pane=new DrawPanel();
         frame.getContentPane().add(pane);
         frame.setVisible(true);
         frame.pack();
         frame.addKeyListener(this);
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         initGame();
         start();
    public void initGame(){
         ship=new Ship();
         ball=new Ball();
    public void start(){
    t=new Thread(this);
         t.start();
        public void run(){
             while(true){
                  try{
                  Thread.sleep(10);
                  }catch(Exception e){}
                  pane.repaint();
    public static void main(String[] args) {
        new BouncingBall();
    public void keyPressed(KeyEvent e){
        switch(e.getKeyCode()){
               case KeyEvent.VK_UP:
               dy--;
               if(dy<MAXSPEED){
               ship.move(0,dy);
               else{
               dy=MAXSPEED;
               ship.move(0,dy);
               break;
               case KeyEvent.VK_LEFT:
                    theta++;
                    break;
               case KeyEvent.VK_RIGHT:
                    theta--;
                    break;     
    repaint();
    public void keyReleased(KeyEvent e){
        switch(e.getKeyCode()){
               case KeyEvent.VK_UP:
               case KeyEvent.VK_DOWN:
               dy=0;     
               break;
    repaint();
    public void keyTyped(KeyEvent e){
    class Ball{
          double x;
          double y;
         private Arc2D.Double body;
         public Ball(){
              x=600.0;
              y=500.0;
              body=new Arc2D.Double(x,y,30.0,30.0,0.0,360.0,Arc2D.OPEN);
         public void move(double dx,double dy){
              body=new Arc2D.Double();
              x+=dx;
              y+=dy;
              body=new Arc2D.Double(x,y,30.0,30.0,0.0,360.0,Arc2D.OPEN);
         public double getX(){
         return this.x;
         public double getY(){
         return this.y;
    class Ship{
          double x;
          double y;
          double angle;         
         private Polygon body;
         public Ship(){
              x=400.0;
              y=300.0;
              angle=0;
              body=new Polygon();
              body.addPoint((int)Math.round(x),(int)Math.round(y));
              body.addPoint((int)Math.round(x+15),(int)Math.round(y));
              body.addPoint((int)Math.round(x+7.5),(int)Math.round(y-20));
         public void move(double dx,double dy){
              body=new Polygon();
              x+=dx;
              y+=dy;
              body.addPoint((int)Math.round(x),(int)Math.round(y));
              body.addPoint((int)Math.round(x+15),(int)Math.round(y));
              body.addPoint((int)Math.round(x+7.5),(int)Math.round(y-20));
         public double getX(){
         return this.x;
         public double getY(){
         return this.y;
    class DrawPanel extends JPanel{
            public DrawPanel(){
              setBackground(Color.black);
              setPreferredSize(new Dimension(BouncingBall.WIDTH,BouncingBall.HEIGHT));
         public void paintComponent(Graphics g){
             super.paintComponent(g);
             Graphics2D g2d=(Graphics2D)g;
             g2d.setColor(Color.white);
             g2d.fill(ball.body);
             g2d.rotate(theta*Math.PI / 180.0);     
             g2d.fill(ship.body);
}Can you guys maybe run this and look over the code and tell me what I'm doing wrong? I would definitely appreciate it Thanks.