/*
 * dif1.java - revised 27 Apr 07 - width 241, height 241
 * @author jackord@kw.igs.net
 * The Fraunhofer diffraction pattern for light from a helium-neon laser
 *   striking a circular (d=.05 mm) aperture and falling on a screen 1 m away
 *   (one pixel representing 1 mm on the screen).
 * The pattern is calculated directly by superposition of Huygens' wavelets.
 * The plot is overexposed 1000X to make lower intensity variations visible.   
 * Three algorithms can be selected: A and B are general algorithms,
 *   C is a specific algorithm for Fraunhofer diffraction.
 */

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

public class dif1 extends Applet 
                  implements ActionListener {
  int kk=0; int first=0;                               // Declarations
  String b1s = "Alg A"; Button b1 = new Button(b1s);
  String b2s = "Alg B"; Button b2 = new Button(b2s);
  String b3s = "Alg C"; Button b3 = new Button(b3s);

  public void init() {
    add(b1); b1.addActionListener(this);
    add(b2); b2.addActionListener(this);
    add(b3); b3.addActionListener(this);
    setBackground(new Color(211, 211, 211));
    setFont(new Font("Helvetica", Font.PLAIN, 12));
  }

  public void paint(Graphics g) {                      // Main Program
    if (first==0) {
      b1.setBounds(2, 2, 40, 20);
      b2.setBounds(44, 2, 40, 20);
      b3.setBounds(86, 2, 40, 20);
      first=1;
    }
    g.setColor(Color.black); g.drawRect(0, 0, 240, 240);
    double la=.633/1000;                               // Helium-neon red
    double d, dd, xg, ygsq, z, zz, pi, a, r, r0, sr, si, t, sc;
    int [] c=new int[169];
    int n, nm, nr, x0, y0;
    x0=120; y0=120; 
    pi=Math.PI; d=.05; n=70; dd=d/(2*n+1); z=1000.; zz=z*z;
    nm=(int)(pi*(2*n+1)*(2*n+1)/4); sc=255000./nm/nm;
    long tt=System.currentTimeMillis();
    if (kk==1) {                                       // Algorithm A
      for (int nx=0; nx<=168; nx=nx+1) {               // Screen X loop
        sr=0; si=0;
        for (int j=-n; j<=n; j=j+1) {                  // Aperture Y loop
          ygsq=j*dd*j*dd;
          for (int i=-n; i<=n; i=i+1) {                // Aperture X loop
            xg=i*dd;
            if ((xg*xg+ygsq)<=(d*d/4)) {
              r=Math.sqrt(zz+(nx-xg)*(nx-xg)+ygsq);
              t=2*pi*r/la; a=.5*(1+z/r)*z/r;
              sr=sr+a*Math.cos(t); si=si+a*Math.sin(t);
            }
          }
        }
        c[nx]=(int)((sr*sr+si*si)*sc);
        if (c[nx]>255) { c[nx]=255; }
      }
    }
    if (kk==2) {                                       // Algorithm B
      for (int nx=0; nx<=168; nx=nx+1) {               // Screen X loop
        r0=Math.sqrt(zz+nx*nx); sr=0; si=0;
        for (int j=-n; j<=n; j=j+1) {                  // Aperture Y loop
          ygsq=j*dd*j*dd;
          for (int i=-n; i<=n; i=i+1) {                // Aperture X loop
            xg=i*dd;
            if ((xg*xg+ygsq)<=(d*d/4)) {
              r=Math.sqrt(zz+(nx-xg)*(nx-xg)+ygsq);
              t=2*pi*(r-r0)/la; a=.5*(1+z/r)*z/r;
              sr=sr+a*Math.cos(t); si=si+a*Math.sin(t);
            }
          }
        }
        c[nx]=(int)((sr*sr+si*si)*sc);
        if (c[nx]>255) { c[nx]=255; }
      }
    }
    if (kk==3) {                                       // Algorithm C
      for (int nx=0; nx<=168; nx=nx+1) {               // Screen X loop
        r0=Math.sqrt(zz+nx*nx); sr=0; si=0;
        for (int j=-n; j<=n; j=j+1) {                  // Aperture Y loop
          ygsq=j*dd*j*dd;
          for (int i=-n; i<=n; i=i+1) {                // Aperture X loop
            xg=i*dd;
            if ((xg*xg+ygsq)<=(d*d/4)) {
              t=2*pi*nx*xg/r0/la; a=.5*(1+z/r0)*z/r0;
              sr=sr+a*Math.cos(t); si=si+a*Math.sin(t);
            }
          }
        }
        c[nx]=(int)((sr*sr+si*si)*sc);
        if (c[nx]>255) { c[nx]=255; }
      }
    }
    if (kk>0) {
      long tc=System.currentTimeMillis();
      for (int ny=0; ny<=119; ny=ny+1) {               // Screen Y loop
        for (int nx=0; nx<=119; nx=nx+1) {             // Screen X loop
          nr=(int)(Math.sqrt(nx*nx+ny*ny));
          Color col=new Color(c[nr], 0, 0);
          g.setColor(col);
          g.drawLine(x0+nx, y0+ny, x0+nx, y0+ny);      // Plot intensity
          g.drawLine(x0-nx, y0+ny, x0-nx, y0+ny);      //   assuming symmetry
          g.drawLine(x0+nx, y0-ny, x0+nx, y0-ny);        
          g.drawLine(x0-nx, y0-ny, x0-nx, y0-ny);        
        }
      }
      long tp=System.currentTimeMillis();
      g.setColor(Color.white);
      g.drawString("Calculate "+(tc-tt)+" ms  Display "+(tp-tc)+" ms", 5, 235);
      kk=0;
    }
  }

  public void actionPerformed(ActionEvent e) {         // Button
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) { kk=1; }
    if (b2s.equals(tst)) { kk=2; }
    if (b3s.equals(tst)) { kk=3; }
    repaint();
  }
}