/*             
 * df1.java - revised 28 Jan 10 - width 481, height 241
 * @author jackord@kw.igs.net
 * The diffraction pattern and intensity graph for a circular aperture of
 *   diameter d viewed on a screen 10*d from the aperture
 *   for various values of the wavelength.
 * The pattern is overexposed 2X.   
 */

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

public class df1 extends Applet 
                  implements ActionListener {
  int kk=0; int first=0;                               // Declarations
  String bs = "Run"; Button bb = new Button(bs);
  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("d/10"); ch.addItem("d/20");
    ch.addItem("d/40"); ch.addItem("d/80");
    ch.addItem("d/120"); ch.addItem("d/160");
    setLayout(new FlowLayout(FlowLayout.LEFT));
    add(ch); add (bb);
    bb.addActionListener(this);
    ch.select(0);
  }

  public void paint(Graphics g) {                      // Main Program
    g.setColor(Color.black); g.drawRect(0, 0, 480, 240);
    g.drawLine(240, 0, 240, 240);
    g.drawLine(312, 0, 312, 240); g.drawLine(408, 0, 408, 240);
    g.drawArc(72, 72, 96, 96, 0, 360);
    double [] la=new double[6];
    double pi, a, d, dd, r, r0, sr, si, t, xg, ygsq, z, zz, cm;
    double [] c=new double[169];
    int cc, n, na, nr, nd, xorg, yorg, x0, x2;
    pi=Math.PI; n=70; d=96.; dd=d/(2*n+1); z=10*d; zz=z*z; cm=0; 
    xorg=120; yorg=120; x0=360; 
    la[0]=d/10; la[1]=d/20; la[2]=d/40;
    la[3]=d/80; la[4]=d/120; la[5]=d/160;
    nd=ch.getSelectedIndex();                          // Wavelength index
    if (kk>0) {
      long tt=System.currentTimeMillis();
      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=0; j<=n; j=j+1) {                   // Aperture Y loop
          ygsq=j*j*dd*dd; na=(int)(Math.sqrt(n*n-j*j));
          for (int i=-na; i<=na; 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[nd]; a=(1+z/r)*z/r; if (j==0) { a=a/2; }
              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 ny=0; ny<=119; ny=ny+1) {               // Pattern Y loop
        for (int nx=0; nx<=119; nx=nx+1) {             // Pattern X loop
          nr=(int)(Math.sqrt(nx*nx+ny*ny));
          cc=(int)(510.*c[nr]/cm); if (cc>255) { cc=255; }
          Color col=new Color(cc, 0, 0);
          g.setColor(col);                             // Plot pattern
          g.drawLine(xorg+nx, yorg+ny, xorg+nx, yorg+ny); 
          g.drawLine(xorg-nx, yorg+ny, xorg-nx, yorg+ny); 
          g.drawLine(xorg+nx, yorg-ny, xorg+nx, yorg-ny);        
          g.drawLine(xorg-nx, yorg-ny, xorg-nx, yorg-ny);        
        }
      }
      g.setColor(Color.white); g.drawArc(72, 72, 96, 96, 0, 360);
      g.setColor(Color.red);
      for (int nx=0; nx<=119; nx=nx+1) {               // Intensity X loop
        x0=360; x2=240-(int)(239*c[nx]/cm);
        if ((nx!=48)&&(x2<240)) {
          g.drawLine(x0+nx, x2, x0+nx, 239);           // Plot intensity
          g.drawLine(x0-nx, x2, x0-nx, 239);           
        }
      }
    }
    kk=0;
  }

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