/*
 * dif4.java - revised 31 Jan 07 - width 241, height 241
 * @author jackord@kw.igs.net
 * The diffraction pattern for light from a helium-neon laser
 *   striking a rectangular (w=0.05 mm, h=.033 mm) or equilateral triangular
 *   aperture (side=.05 mm) and falling on a screen 1 m away
 *   (one pixel representing 1 mm on the screen).
 * The plot is "overexposed" to make lower intensity variations visible.
 * When "AlgD" is selected, Algorithm D replaces Algorithm C for rectangle
 * When "la/6" is selected, the wavelength is divided by 6.
 */

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

public class dif4 extends Applet 
                  implements ActionListener {
  int kk=0; int first=0;                               // Declarations
  String b1s = "Rect"; Button b1 = new Button(b1s);
  String b2s = "Tri"; Button b2 = new Button(b2s);
  Checkbox cha=new Checkbox("AlgD");
  Checkbox chb=new Checkbox("la/6");

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

  public void paint(Graphics g) {                      // Main Program
    if (first==0) {
      b1.setBounds(5, 5, 50, 20);
      b2.setBounds(5, 30, 50, 20);
      cha.setBounds(5, 55, 50, 20);
      chb.setBounds(5, 80, 50, 20);
      first=1;
    }
    double la=.633/1000;                               // Helium-neon red
    double b, by, d, dd, z, zz, a, r0, qr, qi, rr, ri, sr, si, t, sc;
    int c, n, nc, nm, nr, x0, y0;
    double pi=Math.PI;
    g.setColor(Color.black);                           // Initial screen
    g.drawRect(0, 0, 240, 240);
    n=20; nc=13; nr=0;
    d=.05; dd=d/(2*n+1); x0=120; y0=120; z=1000.; zz=z*z; 
    if (chb.getState()==true) { la=la/6; }             // lambda/6
    long tt=System.currentTimeMillis();
    if (kk==1) {                                       // Rectangle
      nm=(2*n+1)*(2*nc+1); sc=255000./nm/nm;
      for (int ny=0; ny<=119; ny=ny+1) {               // Screen Y loop
        for (int nx=0; nx<=119; nx=nx+1) {             // Screen X loop
          r0=Math.sqrt(zz+nx*nx+ny*ny); sr=0; si=0;    
          a=.5*(1+z/r0)*z/r0; b=2*pi*dd/r0/la;
          if (cha.getState()==true) {                  // Algorithm D
            for (int i=-n; i<=n; i=i+1) {              // Aperture X loop
              t=b*(i*nx-nc*ny); 
              sr=sr+Math.cos(t); si=si+Math.sin(t);
            }
            qr=sr; qi=si;
            for (int i=1; i<=2*nc; i=i+1) {            // Aperture Y loop
              rr=Math.cos(i*b*ny); ri=Math.sin(i*b*ny);
              qr=qr+rr*sr-ri*si; qi=qi+rr*si+ri*sr;
            }
            c=(int)((qr*qr+qi*qi)*a*a*sc);              
          }
          else {                                       // Algorithm C
            for (int j=-nc; j<=nc; j=j+1) {            // Aperture Y loop
              for (int i=-n; i<=n; i=i+1) {            // Aperture X loop
                t=b*(i*nx+j*ny); 
                sr=sr+Math.cos(t); si=si+Math.sin(t);
              }
            }
            c=(int)((sr*sr+si*si)*a*a*sc);
          }
          if (c>255) { c=255; }                        // Overexpose
          Color col=new Color(c, 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);        
        }
      }
      g.setColor(Color.white);                         // Show
      g.drawRect(x0-n, y0-nc, 2*n, 2*nc);              // aperture orientation
      g.drawString(""+(System.currentTimeMillis()-tt)+" ms", 5, 235);
    }
    if (kk==2) {                                       // Triangle 
      nm=(2*n+1)*(n+1); sc=255000./nm/nm;              // Algorithm C
      for (int ny=-119; ny<=119; ny=ny+1) {            // Screen Y loop
        for (int nx=0; nx<=119; nx=nx+1) {             // Screen X loop
          r0=Math.sqrt(zz+nx*nx+ny*ny); sr=0; si=0; nr=0;
          a=.5*(1+z/r0)*z/r0; b=2*pi*dd/r0/la;
          by=b*Math.sqrt(3)/2;                         // Close-packed array
          for (int j=-2*n/3; j<=4*n/3; j=j+1) {        // Aperture Y loop
            for (int i=-n; i<=n-nr; i=i+1) {           // Aperture X loop
              t=b*nx*(i+.5*nr)+by*ny*j; 
              sr=sr+Math.cos(t); si=si+Math.sin(t);
            }
            nr=nr+1;
          }
          c=(int)((sr*sr+si*si)*a*a*sc);               // Overexpose 
          if (c>255) { c=255; }                        // and cut off max
          Color col=new Color(c, 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);      // assming x symmetry
        }
      }
      g.setColor(Color.white);                         // Show
      g.drawLine(x0-n, y0+12, x0+n, y0+12);            // aperture orientation
      g.drawLine(x0+n, y0+12, x0, y0-24);
      g.drawLine(x0, y0-24, x0-n, y0+12);
      g.drawString(""+(System.currentTimeMillis()-tt)+" ms", 5, 235);
    }
    kk=0;
  }

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