/**
  * Sigmoid Function Generator
  * @author Robert John Morton Email
  * @version 15 December 1997
*/

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


public class sigmoid extends JPanel implements Runnable{

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

  private double 
    k=.025,   // non-linearity constant
    x=0,      // input value
    y=k/4,    // output value
    dx=k/10;  // T (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,  // width of graph (pixels)
    Y=200,  // height of graph (pixels)
    ph=0,   // horizontal pixel positions of previous pass
    pv=0;   // vertical pixel positions of previous pass

  private long 
    δt=50,  // total Time Frame for T update cycle
    t;      // time at which next new cycle is due to begin

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

  private Font
    font=new Font("Dialog",Font.PLAIN,12);  // annotations font

  private BufferedImage I = null;  // reference for a Graph image object
  private Graphics2D i;            // graphics reference for off-screen image
  private volatile Thread T;       // thread reference variable

  sigmoid() {
    setBackground(bg);  // set applet's background colour

    // Create image object on which to draw graph axes 
    I = new BufferedImage(X,Y,BufferedImage.TYPE_INT_RGB);

    i = I.createGraphics();  // get its graphics context
    i.setColor(bg);          // set background colour of off-screen image
    i.fillRect(0,0,X,Y);     // paint background of off-screen image
    i.setColor(Color.white); // set colour for drawing the graph axes
    i.drawLine(0,V,X,V);     // draw x axis
    i.drawLine(H,0,H,Y);     // draw y axis
    int
      Xy = V - 5,  // x-coord of axis letters
      Yx = H + 5;  // y-co-ord of axis letters

    i.setFont(font);  // set up the annotation font

    i.drawString("X",X-10,Xy);

    i.drawString("Y",Yx,10);  // print the X and Y axis letters
    i.setColor(tr);           // set colour to paint the trace on image

    // Set end time for first update time frame
    t = System.currentTimeMillis() + δt;

    T = new Thread(this);  // create the run thread
    T.start();             // start the run thread
  }


  public void paint(Graphics g) {  // set up the graphics
    g.drawImage(I,14,15,null);     // (re)draw from the off-screen image I
  }


  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 {                 // if not yet finished T graph
      int
        h = (int)(s * x),      // convert horizontal plot to pixels
        v = V - (int)(s * y);  // convert vertical plot to pixels

      if(firstpass){
        ph = h;
        pv = v;
        firstpass = false;
      }
      i.drawLine(ph,pv,h,v);  // do next plot on off-screen image

      ph = h;  // save horizontal pixel positions ready for next pass
      pv = v;  // save verticalpixel 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 T thread
    while(T != null) {  // loop while thread is alive
      newplot();
      if(!finished)     // If not yet finished,
        repaint();      // do the next plot.

      // Time left in the current time-frame.
      long s = t - System.currentTimeMillis();

      if(s < 5)  // in case the PC too slow for the trace speed
        s = 5;

      /* Sleep for the remainder of the time-frame, while
      allowing external events to interrupt the thread. */

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

      // Set the finishing pass of the next time frame.
      t = System.currentTimeMillis() + δt;
    }
  }

  public void stop() { T = null; }  // kill the program thread
}