/**
  * Sigmoid Function Generator
  * @author Robert John Morton UK-YE572246C
  * @version 15 December 1997
*/

import java.awt.*;

public class sigmoid2 extends java.applet.Applet implements Runnable {

  private boolean 
    finished = false,  // indicates when the curve has been completed
    firstpass = true;  // first pass flag

  private double 
    k = 0.025,    // non-linearity constant
    x = 0,        // input value
    y = k / 4,    // output value
    dx = k / 10;  // plotting (or look-up table) increment

  private int 
    s = 200,    // pixels per unit real (scaling factor)
    H = 0,      // horizontal window co-ordinate of graphical origin
    V = s - 1,  // vertical window co-ordinate of graphical origin

    X = 200, Y = 200,  // dimensions (in pixels) of the applet window
    ph = 0, pv = 200,  // horiz and vert pixel positions of previous pass
    mx = 14, my = 15;  // x and y margins for the applet

  private Image I = null;     // reference for an off-screen image I
  private Graphics i = null;  // graphics context for the off-screen image

  private long 
    TF = 100,  // total Time Frame for plotting update cycle
    T;         // time at which next new cycle is due to begin

  private volatile Thread TH;  // thread reference variable

  // lettering font for applet
  private Font font = new Font("Dialog",Font.PLAIN,12);

  private Color 
    bg = new Color(0,0,0),      // background colour
    tr = new Color(0,255,128);  // trace colour

  
  public void init(){           // INITIALISE THE APPLET
    setBackground(bg);          // set applet's background colour
//  Dimension d = getSize();    // get size of window from HTML tag
//  X = d.width; Y = d.height;  // establish window width and height
    I = createImage(X, Y);      // create the off-screen image I
    i = I.getGraphics();        // graphics context for off-screen image

    // For the off-screen image, paint image in background colour 
    i.setColor(bg);
    i.fillRect(0,0,X,Y);

    // Set colour for the graph axes and draw them.
    i.setColor(Color.white);
    i.drawLine(0, V, X, V);
    i.drawLine(H, 0, H, Y);
    int
      Xy = V - 5,  // co-ords of axis letters
      Yx = H + 5;
    i.setFont(font);                // set up the annotation font
    i.drawString("X", X - 10, Xy);  // print the X and Y axis letters
    i.drawString("Y", Yx, 10);

    i.setColor(tr);   // set colour to paint the trace on the image

    // Set thesystem time at which the first time frame will terminate.
    T = System.currentTimeMillis() + TF;
  }


  /* Set up the graphics by re-drawing from the off-screen 
  image I in the event that the applet becomes un-eclipsed. */
  public void paint(Graphics g){ g.drawImage(I, mx, my, null); }

  /* Set up the graphics by re-drawing from the 
  off-screen image I whenever repaint() is called. */
  public void update(Graphics g){ g.drawImage(I,mx,my,null); }


  public void newplot() {  // PLOT THE SIGMOID GRAPH
    if(x > 1 || y > 1)  // if plot has reached edge of graph,
      finished=true;    // set the 'finished' flag
    else {              // else plot has not reached edge of graph
      int 
        h = (int)(s * x),      // convert horizontal plot to pixels
        v = V - (int)(s * y);  // convert vertical plot to pixels

      if(firstpass || h > ph) {

        /* Set the colour to paint the trace on the off-screen
        image and do next plot on the off-screen image. */

        i.drawLine(ph,pv,h,v);
        ph = h;
        pv = v;  // save pixel positions ready for next pass
      }
      y += k * y * (1 - y);  // advance the output difference equation
      x += dx;               // advance the input value
    }
  }


  public void run() {   // run the plotting thread
    while(TH != null){  // loop while thread is alive
      newplot();
      if(!finished)  // if not finished, do next plot
        repaint();

      /* Get the amount of time remaining in the current time
      frame, imposing a minumum limit of 5 milliseconds, then
      put thread to sleep for this remaining amount of time. */

      long s = T - System.currentTimeMillis();
      if (s < 5) s = 5;
      try { TH.sleep(s); }

      /* Catch any events that may occur during thread's sleep but do nothing
      about them because they are normal expected external events. Afterwards,
      set the system time at which the next time frame is due to terminate. */

      catch (InterruptedException e) { }
      T = System.currentTimeMillis() + TF;
    }
  }


  /* Start the program thread by creating the thread object
  and then starting it running [returns a call to run()]. */

  public void start() { TH = new Thread(this); TH.start(); }

  public void stop() {TH = null;}   //Stop program thread
}