/*
 * dif6java - revised 24 Sep 06 - width 241, height 241
 * @author jackord@kw.igs.net
 * The intensity graph for a circular aperture of diameter d or a slit
 *   width d viewed on a screen 10*d from the aperture for various
 *   values of the wavelength.
 * The pattern is calculated directly by superposition of Huygens' wavelets.
 */

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

public class dif6 extends Applet 
                  implements ActionListener {
  int kk=0; int first=0;                               // Declarations
  String bs1 = "Circle"; Button bb1 = new Button(bs1);
  String bs2 = "Slit"; Button bb2 = new Button(bs2);
  Choice ch=new Choice();

  public void init() {                                 
    setBackground(new Color(211, 211, 211));
    ch.setBackground(getBackground());
    setFont(new Font("Helvetica", Font.PLAIN, 12));
    ch.addItem("la=d/5"); ch.addItem("la=d/10");
    ch.addItem("la=d/20"); ch.addItem("la=d/40");
    ch.addItem("la=d/80"); ch.addItem("la=d/120");
    ch.addItem("la=d/160"); ch.addItem("la=d/200"); 
    add(bb1); add(bb2); add (ch);
    bb1.addActionListener(this); bb2.addActionListener(this);
    ch.select(0);
  }

  public void paint(Graphics g) {                      // Main Program
    if (first==0) {                                    // Screen Layout
      bb1.setBounds(4, 28, 40, 20);
      bb2.setBounds(4, 52, 40, 20);
      ch.setBounds(4, 4, 80, 4);
      first=1;
    }
    double [] la=new double[8];
    double [] c =new double[120];
    double d, dd, xg, yg, z, zz, pi, a, r, r0, sr, si, t, cm;
    int n, nd, x0, x2;
    pi=Math.PI; d=96.; n=70; dd=d/(2*n+1);
    z=10*d; zz=z*z; a=1; cm=0; x0=120;
    la[0]=d/5; la[1]=d/10; la[2]=d/20; la[3]=d/40; la[4]=d/80; 
    la[5]=d/120; la[6]=d/160; la[7]=d/200;  
    nd=ch.getSelectedIndex();                          // Wavelength index
    g.setColor(Color.black); g.drawRect(0, 0, 240, 240);
    g.drawLine(72, 0, 72, 240); g.drawLine(168, 0, 168, 240);
    if (kk>0) {
      g.setColor(Color.red);
      for (int nx=0; nx<=119; nx=nx+1) {               // Screen loop
        r0=Math.sqrt(zz+nx*nx); sr=0; si=0;            // Algorithm B
        if (kk==1) {
          for (int j=-n; j<=n; j=j+1) {                // Circle Y loop
            yg=j*dd;
            for (int i=-n; i<=n; i=i+1) {              // Circle X loop
              xg=i*dd;
              if ((xg*xg+yg*yg)<=(d*d/4)) {
                r=Math.sqrt(zz+(nx-xg)*(nx-xg)+yg*yg);
                t=2*pi*(r-r0)/la[nd]; a=.5*(1+z/r)*z/r;// Angle and distance factors
                sr=sr+a*Math.cos(t); si=si+a*Math.sin(t);
              }
            }
          }
        }
        if (kk==2) {
          for (int j=-n; j<=n; j=j+1) {                // Slit loop
            xg=j*dd;
            r=Math.sqrt(zz+(nx-xg)*(nx-xg));
            t=2*pi*(r-r0)/la[nd];
            a=.5*(1+z/r)*Math.sqrt(z/r);               // Angle and distance factors
            sr=sr+a*Math.cos(t); si=si+a*Math.sin(t); 
          }
        }
        c[nx]=sr*sr+si*si; if (c[nx]>cm) { cm=c[nx]; }
      }
      for (int nx=0; nx<=119; nx=nx+1) {
        x2=240-(int)(c[nx]/cm*239);
        if ((nx!=48)&&(x2<240)) {
          g.drawLine(x0+nx, x2, x0+nx, 239);           // Plot intensity
          g.drawLine(x0-nx, x2, x0-nx, 239);           //   assuming symmetry
        }
      }
    }
    kk=0;
  }

  public void actionPerformed(ActionEvent e) {         // Buttons
    String tst;
    tst=e.getActionCommand();
    if (bs1.equals(tst)) { kk=1; }
    if (bs2.equals(tst)) { kk=2; }
    repaint();
  }
}