/*
 * df6.java - revised 20 Dec 2010 - width 321, height 241
 * @author jackord@kw.igs.net
 * Transmitted and Reflected X-ray diffraction patterns from a face-centred
 *   cubic crystal structure.
 * Huygens' wavelets are superimposed from an nxnxn close-packed rhombohedral
 *   array where n is scanned from = 2 to 256.
 * The incident beam is normal to a close-packed plane, and the wavelength
 *   is set to the cube edge divided by the root of 3 to enhance diffraction
 *   from (200) and (220) planes.
 */

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

public class df6 extends Applet 
                  implements ActionListener {
  int kk=0; int first=0;                               // Declarations
  String b1s="Transmit"; Button b1=new Button(b1s);
  String b2s="Reflect"; Button b2=new Button(b2s);
  Image bim;
  Graphics bgr;

  public void init() {
    add(b1); b1.addActionListener(this);
    add(b2); b2.addActionListener(this);
    setBackground(new Color(211, 211, 211));
    setFont(new Font("TimesRoman", Font.PLAIN, 12));
  }

  public void paint(Graphics g) {                      // Main Program
    b1.setBounds(10, 5, 60, 20);
    b2.setBounds(10, 28, 60, 20);
    int c, di, ni, x0, y0, del; long tt;
    double a, b, d, dx, dy, dz, lam, z, zz, r0, qr, qi, rr, ri, sr, si, t, sc, sn;
    double la;
    if (first==0) {
      bim=createImage(240, 240);
      bgr=bim.getGraphics();
      first=1;
    }
    a=3.615E-7; x0=120; y0=120; z=30.; zz=z*z;         // Cu lattice parameter
    d=a/Math.sqrt(2.); la=a/Math.sqrt(3);
    double pi=Math.PI;
    g.setColor(Color.black);                           // Initial screen
    g.drawRect(0, 0, 320, 240);
    if (kk==1) di=1; else di=-1;                       // Transmit / Reflect
    if (kk>0) {                                        
      for (int n=1; n<=8; n=n+1) {
        for (int ny=-120; ny<=120; ny=ny+1) {          // Screen Y loop
          for (int nx=-120; nx<=120; nx=nx+1) {        // Screen X loop
            r0=Math.sqrt(zz+nx*nx+ny*ny);
            b=2*pi/r0/la;
            sr=1; si=0; ni=1; sn=1.0; dx=d;
            for (int i=1; i<=n; i=i+1) {               // Array X loop
              t=b*ni*dx*nx;
              rr=Math.cos(t); ri=Math.sin(t);
              qr=sr+rr*sr-ri*si; si=si+rr*si+ri*sr;
              sr=qr; ni=2*ni; sn=2*sn;
            }
            ni=1; dx=d/2; dy=d*Math.sqrt(3.)/2;        // Array Y loop
            for (int i=1; i<=n; i=i+1) {                 
              t=ni*b*(dx*nx+dy*ny);
              rr=Math.cos(t); ri=Math.sin(t);
              qr=sr+rr*sr-ri*si; si=si+rr*si+ri*sr;
              sr=qr; ni=2*ni; sn=2*sn;
            }
            ni=1; dy=d/2/Math.sqrt(3.); dz=d/Math.sqrt(1.5);
            for (int i=1; i<=n; i=i+1) {               // Array Z loop 
              t=ni*b*(dx*nx+dy*ny+dz*(di*z-r0));
              rr=Math.cos(t); ri=Math.sin(t);
              qr=sr+rr*sr-ri*si; si=si+rr*si+ri*sr;
              sr=qr; ni=2*ni; sn=2*sn;
            }
            sc=2550/sn/sn;                             // Intensity scale
            c=(int)((sr*sr+si*si)*sc);
            if (c>255) { c=255; }                        
            Color col=new Color(0, c, 0);
            bgr.setColor(col);
            bgr.drawLine(x0+nx, y0-ny, x0+nx, y0-ny);  // Plot intensity
          }
        }
        bgr.setColor(Color.white);
        bgr.drawString("FCC   n = "+(int)(Math.pow(2, n)), 5, 235);
        g.drawImage(bim, 80, 0, null);                 // Show plot buffer
        tt=System.currentTimeMillis();
      while ((System.currentTimeMillis()-tt)<1000) { }
      }
    }
    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();
  }
}