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

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

public class sigfun extends JPanel implements Runnable {
  private boolean 
    finished = false,  // indicates when the curve has been completed
    TypeFlag = false;  // set for unipolar presentation

  private double 
    k = .025,     // non-linearity constant
    y = k / 4,    // output value
    x = 0,        // input 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,    // x-extent (in pixels) of the applet window
    Y = 200;    // y-extent (in pixels) of the applet window

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

  private Font font = new Font("Dialog",Font.PLAIN,12);  // for annotations
  private Color tr = new Color(0,255,128);               // trace colour

  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


  sigfun(boolean b) {
    TypeFlag = b;  // false = monopolar; true = bipolar trace
    int
      Xy = V - 5,  // x-coord of axis letters 
      Yx = H + 5;  // y-coord of axis letters 

    // 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

    if(TypeFlag){   // if doing a bipolar trace,
      k = 0.011;    // non-linearity constant
      x = 0;        // input value
      y = 0;        // output value
      dx = .0025;   // T (or look-up table) increment
      s = 100;      // pixels per unit real (scaling factor)
      H = 100;      // horizontal window co-ordinate of graphical origin 
      V = 100;      // vertical window co-ordinate of graphical origin 
      Xy = V + 15;  // x-coord of axis letters
      Yx = H - 10;  // y-coord of axis letters
    }
    i.setColor(Color.black);  // background colour for off-screen image
    i.fillRect(0,0,X,Y);      // paint background of off-screen image
    i.setFont(font);          // set up the annotation font
    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
    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
  }


  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
      int v = (int)(s * y);  // convert vertical plot to pixels

      int
        a = h,        // simplify pixel co-ordinates
        b,
        c = V - v,
        d;
      if(TypeFlag) {
        a = H - h;    // simplify pixel co-ordinates
        b = H + h;
        c = V + v;
        d = V - v;
        i.drawLine(b,d,b,d);   // do next plot in lower left quadrant
        y += k * (1 - y);      // advance the output difference equation
      } else  
        y += k * y * (1 - y);  // advance the output difference equation

      x += dx;              // advance the input value
      i.drawLine(a,c,a,c);  // do next plot in upper right quadrant
    }
  }


  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 PC too slow for plotting 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
}