/** Henon's Strange Attractor Generator by Robert J Morton 30 October 1997 */

import java.awt.*;
import javax.swing.*;
import java.awt.image.BufferedImage;

public class hengraph extends JPanel implements Runnable {

  private int
    XE,           // Horizontal extent of window and JFrame.
    YE,           // Vertical extent of window and JFrame.
    XBIAS = 150,  // pixel co-ordinates of real point 0,0 
    YBIAS = 150,
    XMAX  = 300,  // dimensions of the display area (pixels)
    YMAX  = 300,
    i,            // Pixel co-ordinates of chaotic body
    j;            // within the visible xy plane.

  private long 
    tf = 150,     // inter-plot time frame (milliseconds)
    t;            // current system time
  private double 
    Scale = 100,  // pixels per unit real eg 100 pixels = 1.00d
    x = 0,        // real co-ordinates of 'chaotic body'
    y = 0, 
    z;

  private Color 
    A[][],              // pixel colour array
    colour,             // current plot colour
    bgc = Color.black,  // background colour

    fgc = new Color(0,255,128),  // bright green for trace
    axc = new Color(96,128,0);   // special browny-green for axes 64,192,0

  private BufferedImage I;  // off-screen image on which to plot the graph
  private Graphics2D gi;    // graphics reference for off-screen image
  private Thread T;         // declare a thread reference variable


  public hengraph(int XE, int YE) {
    this.XE = XE;          // horizontal [X] dimension of the JPanel
    this.YE = YE;          // vertical [Y] dimension of the JPanel
    setBounds(0,0,XE,YE);  // the JPanel fills the whole of the JFrame area
    setLayout(null);       // JPanel has free-form layout [for graph]

    /* Create a Buffered Image "I" on which to plot Henon's Attractor off-
    screen and get its graphics context "gi" for realising the plots. */

    I = new BufferedImage(XE,YE,BufferedImage.TYPE_INT_RGB);
    gi = I.createGraphics();

    A = new Color[XMAX][YMAX];  // create colour array for the display area

    for(i = 0; i < XMAX; i++)   // clear the colour array to background colour
      for(j = 0; j < YMAX; j++)
        A[i][j] = bgc;

    for(i = 0; i < XMAX; i++)   // c reate the x-axis graticule
      A[i][YBIAS] = axc;
    for(j = 0; j < YMAX; j++)   // create the y-axis graticule
      A[XBIAS][j] = axc;

    // Set the system time at which the next plot's time frame must end. 
    t = System.currentTimeMillis() + tf;

    T = new Thread(this);  // creating the thread object
    T.start();             // and starting it running by
  }                                       


  public void paint(Graphics g) {  // PAINT / RE-PAINT THE PICTURE SO FAR
    g.drawImage(I,20,20,this);     // display the buffered image
  }


  private void initialPlot() {
    for(j = 0; j < YMAX; j++) {  // for each of the YMAX lines in the picture

      int I = 0;  // starting dot of next single-colour stretch of line
      i = 0;      // to find next pixel in current line with different colour
 
      colour = A[I][j];  // make colour of first dot the reference colour

      // While not yet reached the end of the current line... 
      while(++i < XMAX) {

        // if this dot is a different colour from the previous dot...
        if(colour != A[i][j]){
          gi.setColor(colour);     // set colour to colour of previous dot
          gi.drawLine(I,j,i-1,j);  // draw line from start dot to previous dot
          colour = A[I = i][j];    // make reference colour that of this dot
        }
      }
      gi.setColor(colour);     // set colour for final stretch of current line
      gi.drawLine(I,j,i-1,j);  // draw the last stretch of the current line
    }
  }


  private void currentPlot(){
    z = x;                       // z inherits last time's value of x
    x = 1.4*x*x+0.3*y-1;         // advance x
    y = z;                       // advance y
    int i=XBIAS+(int)(x*Scale);  // Compute the pixel co-ordinates
    int j=YBIAS-(int)(y*Scale);  // corresponding to new values of x and y.
    A[i][j] = fgc;               // put the plot on the 'canvas'
    gi.setColor(fgc);            // set colour for plot
    gi.drawLine(i,j,i,j);        // draw the plot in the applet window
  }


  public void run() {  // run the Track Recorder painting thread
    initialPlot();
    while(true) {      // permanent loop
      currentPlot();
      repaint();       // paint in the next plot

      /* Get the time left in this plot's time frame and if it
      is less than 5 milliseconds, set it to 5 milliseconds. */

      long s = t - System.currentTimeMillis();
      if(s < 5) s = 5;

      /* Sleep for the remainder of the time frame. If an external
      interrupt occurs during this time, catch it and process it. */

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

      // Set the system time at which the next plot's time frame will end.
      t = System.currentTimeMillis() + tf;
    }
  }
}