/*
 * gb2.java - revised 27 Feb 08 - width 409, height 337
 * @author jackord@kw.igs.net
 * equipotentials for -Q, 2Q, -Q charge array
 */

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

public class gb2 extends Applet 
                  implements ActionListener {
  int kk=0;                                            // Declarations
  int [] p=new int[4];
  double [] q=new double[4];
  int [] m=new int[4];
  String bs = "Plot"; Button b = new Button(bs);
  Color col[]={ Color.blue, Color.cyan, Color.red, Color.yellow, Color.magenta, Color.green };

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

  public void pin(Graphics g) {                        // Initialize
    p[1]=121; q[1]=216; p[2]=204; q[2]=216-166*Math.sqrt(3)/2;
    p[3]=287; q[3]=216; m[1]=-1; m[2]=2; m[3]=-1;
    g.setFont(new Font("Arial", Font.PLAIN, 12));
    g.setColor(Color.gray);
    for (int i=1; i<=3; i=i+1) {
      g.fillArc(p[i]-12, (int)(q[i])-12, 25, 25, 0, 360);
    }
    g.setColor(Color.black);
    g.drawRect(0, 0, 408, 336);
    for (int i=1; i<=3; i=i+1) {
      g.drawArc(p[i]-12, (int)(q[i])-12, 24, 24, 0, 360);
    }
    g.drawString("2Q", p[2]-7, (int)(q[2])+5);
    g.drawString("-Q", p[1]-7, (int)(q[1])+5);
    g.drawString("-Q", p[3]-7, (int)(q[3])+5);
  }

  public void paint(Graphics g) {                      // Main Program
    int plt; 
    double r2, u;
    pin(g);
    if (kk>0) {                                        
      for (int k=1; k<=335; k=k+1) {
        for (int j=1; j<=407; j=j+1) {
          u=0; plt=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>144) { u=u+m[i]/Math.sqrt(r2); }
            else { plt=0; }
          }
          if (plt>0) {
            g.setColor(col[(int)(288*(.1+u))%6]);
            g.drawLine(j, k, j, k);
          }
        }
      }
      g.setColor(Color.black);
      for (int i=1; i<=3; i=i+1) {
        g.drawArc(p[i]-12, (int)(q[i])-12, 24, 24, 0, 360);
      }
      kk=0;
    }
  }

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