import java.awt.*;
import java.awt.image.*;
import java.awt.geom.*;
import javax.swing.*;
import java.util.Random;

public class Orbit extends JComponent implements Runnable
{
  int imageWidth, imageHeight;
  double delta = 0.001;
  double xLowerLeft, yLowerLeft, xUpperRight, yUpperRight;
  double pixelWidth, pixelHeight, invPixelWidth, invPixelHeight;
  double[] pv = new double[4];
  double ax, ay;
  int counter = 0;

  Random randNumGen = new Random(5);
  
  BufferedImage bufImage;
  Graphics2D bufImageGraphic;

  public Orbit(int w, int h, double xLL, double yLL, double xUR,
                 double yUR) 
  {
    pv[0] = 1.0; pv[1] = 0.0; pv[2] = 0.0; pv[3] = -1.0;
    imageWidth = w; imageHeight = h;
    xLowerLeft =  xLL; yLowerLeft =  yLL;
    xUpperRight = xUR; yUpperRight = yUR;
  	
    pixelWidth  = (xUR - xLL)/((double)w); 
    invPixelWidth  = ((double)w)/(xUR - xLL);
    pixelHeight = (yUR - yLL)/((double)h); 
    invPixelHeight = ((double)h)/(yUR - yLL);
  	
    System.out.println(imageWidth + "     " + imageHeight);
    System.out.println(pixelWidth + "     " + pixelHeight);
  
    bufImage = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
    bufImageGraphic = bufImage.createGraphics( );
    bufImageGraphic.setPaint(Color.white);
    //bufImageGraphic.setPaint(Color.black);
    bufImageGraphic.fillRect(0, 0, w, h);
    bufImageGraphic.setPaint(Color.blue);
    bufImageGraphic.setStroke(new BasicStroke((float)(0.1*pixelHeight))); 

    AffineTransform at = new AffineTransform(invPixelWidth, 
                                             0, 0, -invPixelHeight,
                                             -invPixelWidth*xLL, 
                                             invPixelHeight*yUR      
                                            );
    bufImageGraphic.setTransform(at);

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

  public void timeStep( )
  { 
    double[] u = new double[4];
    u = DOrbit(pv);
    Line2D.Double L = 
      new Line2D.Double(pv[0], pv[1], u[0], u[1]);
    bufImageGraphic.fill(L);
    pv[0] = u[0]; pv[1] = u[1]; pv[2] = u[2]; pv[3] = u[3];
  }

  public void run( ) 
  {
    try 
    { 
      for(counter = 0; counter < 10000000; ++counter)
      { //Loopbody:
        timeStep( ); 
        repaint( );
        Thread.sleep(0);
      }
    }
    catch (InterruptedException ie) {} 
  }

  double[] DOrbit(double[] s)
  {
    double r = Math.sqrt(s[0]*s[0] + s[1]*s[1]);
    double u[] = new double[4];
    u[0] = delta*s[2] + s[0];
    u[1] = delta*s[3] + s[1];
    u[2] = -delta*s[0]*(1.0/(r*r*r)) + s[2];
    u[3] = -delta*s[1]*(1.0/(r*r*r)) + s[3];
    return u;
  }

  public void paint(Graphics g) 
  {
    Graphics2D g2 = (Graphics2D)g;
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_OFF);
    //g2.setPaint(Color.blue);
    //g2.drawImage(image, imageX, imageY, this);
    g2.drawImage(bufImage, 0, 0, this);
  }

  public static void main(String[] args) 
  {
    JFrame frame = new JFrame("Orbit");
    frame.setBackground(Color.white);
    Orbit plot = new Orbit(800, 800, -2, -2, 2, 2);
    frame.getContentPane( ).add(plot);
    frame.setSize(800, 800);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }

}