/*             
 * dif5.java - revised 24 Sep 06 - width 241, height 241
 * @author jackord@kw.igs.net
 * The diffraction pattern 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 calculated directly by superposition of Huygens' wavelets.
 * The plot is overexposed 2X.   
 */

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

public class dif5 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("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(bb); add (ch);
    bb.addActionListener(this);
    ch.select(0);
  }

  public void paint(Graphics g) {                      // Main Program
    if (first==0) {                                   
      bb.setBounds(5, 30, 30, 20);                     // Screen layout
      ch.setBounds(5, 5, 70, 5);
      first=1;
    }
    g.setColor(Color.black); g.drawRect(0, 0, 240, 240);
    g.drawArc(72, 72, 96, 96, 0, 360);
    double [] la=new double[8];
    double pi, a, d, dd, r, r0, sr, si, t, xg, yg, z, zz;
    int [] c=new int[169];
    int cm, n, nr, nd, xorg, yorg;
    pi=Math.PI; n=48; d=96.; dd=d/(2*n+1); z=10*d; zz=z*z; cm=0; 
    xorg=120; yorg=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
    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;            // Algorithm B
        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)) {
              r=Math.sqrt(zz+(nx-xg)*(nx-xg)+yg*yg);
              t=2*pi*(r-r0)/la[nd]; a=.5*(1+z/r)*z/r;
              sr=sr+a*Math.cos(t); si=si+a*Math.sin(t);
            }
          }
        }
        c[nx]=(int)(sr*sr+si*si); if (c[nx]>cm) { cm=c[nx]; }
      }
      for (int nx=0; nx<=168; nx=nx+1) {               // Overexpose 2X
        c[nx]=(int)(510.*c[nx]/cm); if (c[nx]>255) { c[nx]=255; }
      }
      long tc=System.currentTimeMillis();
      for (int ny=0; ny<=119; ny=ny+1) {               // Screen Y loop
        for (int nx=0; nx<=119; nx=nx+1) {             // Screen X loop
          nr=(int)(Math.sqrt(nx*nx+ny*ny));
          Color col=new Color(c[nr], 0, 0);
          g.setColor(col);                             // Plot intensity
          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);        
        }
      }
      long tp=System.currentTimeMillis();
      g.setColor(Color.white); g.drawArc(72, 72, 96, 96, 0, 360);
      g.drawString("Calculate "+(tc-tt)+" ms  Display "+(tp-tc)+" ms", 5, 235);
    }
    kk=0;
  }

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