/*
 * df2.java - revised 4 Jan 10 - width 301, height 241
 * @author jackord@kw.igs.net
 * The diffraction pattern produced when light from a helium-neon laser
 *   strikes a circular (d=.05 mm) aperture and falls on a screen 1000 mm
 *   away (125 mm if "z/8" is chosen). One pixel represents 1 mm on the screen.     )
 * The plot is "overexposed" to make lower intensity variations visible.   
 * The numerical calculation uses either a square grid with 41 points along d
     (21 if "n/2" is chosen), or a random array of the same number of points.
 */

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

public class df2 extends Applet 
                  implements ActionListener {
  int kk=0; int first=0;                               // Declarations
  String bbs="Plot"; Button bb = new Button(bbs);
  Checkbox ch1=new Checkbox("n/2");
  Checkbox ch2=new Checkbox("z/8");
  Checkbox ch3=new Checkbox("Rnd");

  public void init() {                                 
    add(bb); bb.addActionListener(this);
    add(ch1); add(ch2); add(ch3);
    setBackground(new Color(211, 211, 211));
    ch1.setBackground(getBackground());
    ch2.setBackground(getBackground());
    ch3.setBackground(getBackground());
    setFont(new Font("Helvetica", Font.PLAIN, 12));
  }

  public void paint(Graphics g) {                      // Main Program
    bb.setBounds(10, 5, 40, 20);
    ch1.setBounds(10, 30, 40, 20);
    ch2.setBounds(10, 55, 40, 20);
    ch3.setBounds(10, 80, 40, 20);
    double la=.633/1000;                               // Helium-neon red
    double a, b, d, dd, r0, r2, xg, yg, z, zz, sr, si, t, sc;
    int c, cg, m, n, nm, ns, x0, y0;
    double pi=Math.PI;
    g.setColor(Color.black);                           // Initial screen
    g.drawRect(0, 0, 300, 240);
    if (ch1.getState()==true) { n=10; } else { n=20; }
    if (ch2.getState()==true) { z=125.; } else { z=1000.; }
    x0=180; y0=120; pi=Math.PI; d=.05; dd=d/(2*n+1); zz=z*z;
    r2=0.25*(2*n+1)*(2*n+1); nm=(int)(pi*r2); sc=255000./nm/nm; ns=0;
    long tt=System.currentTimeMillis();
    if (kk>0) {
      if (ch3.getState()==false) {
        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/r0/la;
            for (int j=-n; j<=n; j=j+1) {              // Aperture Y loop
              yg=j*dd; m=(int)(Math.sqrt(r2-j*j));
              for (int i=-m; i<=m; i=i+1) {            // Aperture X loop
                xg=i*dd;
                t=b*(nx*xg+ny*yg);
                sr=sr+a*Math.cos(t); si=si+a*Math.sin(t);
              }
            }
            c=(int)((sr*sr+si*si)*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);    //   assuming symmetry
            g.drawLine(x0+nx, y0-ny, x0+nx, y0-ny);        
            g.drawLine(x0-nx, y0-ny, x0-nx, y0-ny);        
          }
        }
      }
      if (ch3.getState()==true) {
        double[] x=new double[nm+1];
        double[] y=new double[nm+1];
        sc=sc/2;
        while (ns<nm) {
          xg=d*(Math.random()-.5); yg=d*(Math.random()-.5);
          if (xg*xg+yg*yg<=d*d/4) {
            ns=ns+1; x[ns]=xg; y[ns]=yg; 
          }
        }  
        for (int ny=-119; ny<=119; ny=ny+1) {          // Screen Y loop
          for (int nx=-119; 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/r0/la;
            for (int i=1; i<=nm; i=i+1) {              // Array loop
              t=b*(nx*x[i]+ny*y[i]);
              sr=sr+a*Math.cos(t); si=si+a*Math.sin(t);
            }
            c=(int)((sr*sr+si*si)*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.setColor(Color.black);
      g.drawString(""+(System.currentTimeMillis()-tt)+" ms", 2, 235);
      kk=0;
    }
  }

  public void actionPerformed(ActionEvent e) {         // Button
    String tst;
    tst=e.getActionCommand();
    if (bbs.equals(tst)) { kk=1; }
    repaint();
  }
}