/*
 * dif2.java - revised 31 Jan 07 - width 241, 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 1 m away
 *   (one pixel representing 1 mm on the screen).
 * The plot is "overexposed" to make lower intensity variations visible.   
 * The numerical calculation uses either a square grid with n=41 points along
     d, or a random array of n*n points spread over a square of side d.
 */

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

public class dif2 extends Applet 
                  implements ActionListener {
  int kk=0; int first=0;                               // Declarations
  String b1s = "Square"; Button b1 = new Button(b1s);
  String b2s = "Random"; Button b2 = new Button(b2s);

  public void init() {                                 
    add(b1); b1.addActionListener(this);
    add(b2); b2.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(5, 5, 50, 20);
      b2.setBounds(5, 30, 50, 20);
      first=1;
    }
    double la=.633/1000;                               // Helium-neon red
    double a, d, dd, r0, xg, yg, z, zz, sr, si, t, sc;
    int c, n, nm, ns, x0, y0;
    double pi=Math.PI;
    g.setColor(Color.black);                           // Initial screen
    g.drawRect(0, 0, 240, 240);
    x0=120; y0=120; 
    pi=Math.PI; d=.05; n=20; dd=d/(2*n+1); z=1000.; zz=z*z;
    nm=(int)(pi*(2*n+1)*(2*n+1)/4); sc=255000./nm/nm; ns=0;
    long tt=System.currentTimeMillis();
    if (kk==1) {
      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;    // Algorithm C
          for (int j=-n; j<=n; j=j+1) {                // Aperture Y loop
            yg=j*dd;
            for (int i=-n; i<=n; i=i+1) {              // Aperture X loop
              xg=i*dd;
              if ((xg*xg+yg*yg)<=(d*d/4)) {
                t=2*pi*(nx*xg+ny*yg)/r0/la; a=.5*(1+z/r0)*z/r0;
                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);        
        }
      }
      g.setColor(Color.white);
      g.drawString(""+(System.currentTimeMillis()-tt)+" ms", 5, 235);
    }
    if (kk==2) {                                       // Random array
      double[] x=new double[nm+1];
      double[] y=new double[nm+1];
      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;    // Algorithm C
          for (int i=1; i<=nm; i=i+1) {                // Array loop
            t=2*pi*(nx*x[i]+ny*y[i])/r0/la; a=.5*(1+z/r0)*z/r0;
            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.white);
      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();
  }
}