/*
 * mw6.java - revised 23 Apr 07 - width 481, height 241
 * @author jackord@kw.igs.net
 * wave incident (k) on a barrier (ik/n) wave transmitted (k)
 *   (n can have any value, but is set equal to 4 in the example)
 * the barrier width equals the incident wavelength
 * plot shows ONE (real or imaginary) component of the wavefunction
 */

import java.applet.Applet;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class mw6 extends Applet
                 implements ActionListener, Runnable {
  int kk=0; int jd=40; double n=4; int first=0;        // Declarations
  double a, r, a1, r1, a2, r2, t, dt, dx;
  double ph1, ph2, ph3, ph4;
  String b1s="Component"; Button b1=new Button(b1s);
  String b2s="Resultant"; Button b2=new Button(b2s);
  Image bim;
  Graphics bgr;
  Thread tmr;

  public void init() {
    setLayout(new FlowLayout(FlowLayout.LEFT));
    setBackground(new Color(211, 211, 211));
    add(b1); add(b2);
    b1.addActionListener(this);
    b2.addActionListener(this);
  }

  public void start() {
    if (kk>0) {
      if (tmr==null) {
        tmr=new Thread(this);
      }
      tmr.start();
    }
  }

  public void stop() {
    tmr=null;
  }

  public void run() {
    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
    repaint();
  }

  public void pin(Graphics g) {
    double c, s, b, f;
    g.setColor(Color.black);
    g.drawRect(0, 0, 480, 240); g.drawLine(0, 120, 480, 120);
    g.drawLine(240, 0, 240, 240); g.drawLine(360, 0, 360, 240);
    if (first==0) {
      bim=createImage(481, 241);                       // Animation buffer
      bgr=bim.getGraphics();
      first=1;
    }
    dx=Math.PI/20; dt=dx/2; b=2*Math.PI/n;
    c=(Math.exp(-b)+Math.exp(b))/2;                    // Complex arithmetic
    s=(Math.exp(-b)-Math.exp(b))/2;
    f=s*(n-1/n)/2;
    t=1/Math.sqrt(c*c+f*f); ph1=Math.atan2(f, c);
    r1=(n+1/n)*s*t/2; ph2=ph1-Math.PI/2;
    a2=Math.sqrt(1+n*n)*t/2; r2=a2;
    ph4=ph1+Math.atan2(n, 1);
    ph3=ph1-Math.atan2(n, 1);
    a1=60; r1=a1*r1; a2=a1*a2; r2=a1*r2; t=a1*t;       // Amplitudes (finally)
  }

  public void paint(Graphics g) {
    int x1, y1, x2, y2;
    if (kk==0) {
      pin(g);
    }
    else {
      long tt=System.currentTimeMillis(); int del=15;
      for (int i=0; i<=320; i=i+1) {
        bgr.setColor(getBackground());                 // Clear plot buffer
        bgr.fillRect(0, 0, 481, 241);
        bgr.setColor(Color.black); bgr.drawRect(0, 0, 480, 240);
        bgr.drawLine(0, 120, 480, 120); bgr.drawLine( 240, 0, 240, 240);
        bgr.drawLine(360, 0, 360, 240);
        if (kk==1) {
          bgr.setColor(Color.magenta);                 // Plot incident wave
          x1=0; y1=120-(int)(a1*Math.sin(i*dt));
          for (int j=1; j<=80; j=j+1) {                
            a=a1*Math.sin(i*dt-j*dx);
            x2=3*j; y2=120-(int)a;
            bgr.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
          }
          bgr.setColor(Color.red);                     // Plot reflected wave
          x1=0; y1=120-(int)(r1*Math.sin(i*dt+ph2));
          for (int j=1; j<=80; j=j+1) {               
            r=r1*Math.sin(i*dt+j*dx+ph2);
            x2=3*j; y2=120-(int)r;
            bgr.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
          }
          bgr.setColor(Color.orange);                  // Plot barrier region
          x1=240; y1=120-(int)(a2*Math.sin(i*dt+ph3)*Math.exp(-jd*dx/n));
          for (int j=1; j<=jd; j=j+1) {              
            a=a2*Math.sin(i*dt+ph3)*Math.exp((j-jd)*dx/n);
            x2=240+3*j; y2=120-(int)a;
            bgr.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
          }
          bgr.setColor(Color.green);
          x1=240; y1=120-(int)(r2*Math.sin(i*dt+ph4)*Math.exp(jd*dx/n));
          for (int j=1; j<=jd; j=j+1) {                
            r=r2*Math.sin(i*dt+ph4)*Math.exp((jd-j)*dx/n);
            x2=240+3*j; y2=120-(int)r;
            bgr.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
          }
        }
        if (kk==2) {                                   // Plot resultant wave
          bgr.setColor(Color.blue);
          x1=0; y1=120-(int)(a1*Math.sin(i*dt)+r1*Math.sin(i*dt+ph2));
          for (int j=1; j<=80; j=j+1) {                
            a=a1*Math.sin(i*dt-j*dx);
            r=r1*Math.sin(i*dt+j*dx+ph2);
            x2=3*j; y2=120-(int)(a+r);
            bgr.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
          }
          for (int j=1; j<=jd; j=j+1) {                // Plot barrier region
            a=a2*Math.sin(i*dt+ph3)*Math.exp((j-jd)*dx/n);
            r=r2*Math.sin(i*dt+ph4)*Math.exp((jd-j)*dx/n);
            x2=240+3*j; y2=120-(int)(a+r);
            bgr.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
          }
        }
        bgr.setColor(Color.blue);                      // Plot transmitted wave
        x1=240+3*jd; y1=120-(int)(t*Math.sin(i*dt+ph1));
        for (int j=jd+1; j<=80; j=j+1) {                  
          x2=240+3*j; y2=120-(int)(t*Math.sin(i*dt-(j-jd)*dx+ph1));
          bgr.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
        }
        g.drawImage(bim, 0, 0, null);                  // Show plot buffer
        while (System.currentTimeMillis()-tt<30*i) {
          try {
            Thread.sleep(del);
          }
          catch (InterruptedException e) {
            stop();
          }
        }
      }
    }
    kk=0; stop();
  } 

  public void actionPerformed(ActionEvent e) {
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) { kk=1; }
    if (b2s.equals(tst)) { kk=2; }
    start();
  }
}