/*
 * gd1.java - revised 15 Apr 05 - width 205, height 191
 * @author jackord@kw.igs.net
 * solution of Laplace's equation:
 *   128 iterations at 4 pixel steps
 *    16 iterations at 2 pixel steps
 *     6 iterations at 1 pixel steps
 */

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

public class gd1 extends Applet 
                    implements ActionListener {
  int kk=0;                                            // Declarations
  String bs="Plot"; Button b = new Button(bs);
  TextField tx=new TextField(7);
  Color col[]={ Color.blue, Color.cyan, Color.red, Color.yellow, Color.magenta, Color.green };

  public void init() {                                 // Layout
    add(b); add(tx);
    b.addActionListener(this);
    setBackground(new Color(211, 211, 211));
    tx.setBackground(getBackground());
  }

  public void paint(Graphics g) {                      // Main Program
    int d, test;
    long r2;
    int [] p=new int[4];
    int [] q=new int[4];
    double [][] v=new double[205][169];
    b.setBounds(30, 170, 65, 20);
    tx.setBounds(110, 170, 65, 20);
    tx.setText("Pass/150");
    p[1]=60; q[1]=108; p[2]=102; q[2]=36;
    p[3]=144; q[3]=108;
    g.setColor(Color.blue);                            // Boundary (0 V)
    g.drawRect(0, 0, 204, 168);
    g.setColor(Color.red);                             // Cylinders (100 V)
    for (int i=1; i<=3; i=i+1) {
      g.fillArc(p[i]-6, q[i]-6, 12, 12, 0, 360);
    }
    if (kk>0) {
      for (int k=1; k<=167; k=k+1) {                   // Set initial v(i, j)
        for (int j=1; j<=203; j=j+1) {
          test=1;
          for (int i=1; i<=3; i=i+1) {
            r2=(p[i]-j)*(p[i]-j)+(q[i]-k)*(q[i]-k);
            if (r2<=36) {
              test=0;
            }
          }
          if (test>0) {
            v[j][k]=50;
          }
          else {
            v[j][k]=100;
          }
        }
      }
      d=4;
      for (int i=1; i<=150; i=i+1) {                   // Iteration loop
        tx.setText(Integer.toString(i)+"/150");
        for (int k=d; k<=168-d; k=k+d) {
          for (int j=d; j<=204-d; j=j+d) {
            if (v[j][k]<100) {
              v[j][k]=(v[j][k-d]+v[j][k+d]+v[j+d][k]+v[j-d][k])/4;
            }
            g.setColor(col[(int)(v[j][k]/7)%6]);
            if (d<2) {
              g.drawLine(j, k, j, k);
            }
            else {
              g.fillRect(j-d/2, k-d/2, d, d);
            }
          }
        }
        if ((i==128)||(i==144)) {                      // Reduce interval...
          d=d/2;                                                
          for (int k=d; k<=168-d; k=k+2*d) {           // ...and...
            for (int j=2*d; j<=204-2*d; j=j+2*d) {
              if (v[j][k]<100) {
                v[j][k]=(v[j][k-d]+v[j][k+d])/2;
              }
            }
          }
          for (int k=d; k<=168-d; k=k+d) {             // ...interpolate
            for (int j=d; j<=204-d; j=j+2*d) {
              if (v[j][k]<100) {
                v[j][k]=(v[j-d][k]+v[j+d][k])/2;
              }
            }
          }
        }
      }
      tx.setText("Finished");
      kk=0;                    
    }
  }

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