/*
 * fosc.java - revised 7 Apr 05 - width 401, height 401
 * @author jackord@kw.igs.net
 * phase diagram for the damped oscillator
 *   - overdamped: Q = 1/3
 *   - critical damping: Q = 1/2
 *   - underdamped: Q = 1
 */

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

public class fosc extends Applet 
                   implements ActionListener {
  int kk=0;                                            // Declarations
  String b1s="Plot"; Button b1=new Button(b1s);
  Choice cho1=new Choice();

  public void init() {
    cho1.addItem("Q=1"); cho1.addItem("Q=1/2"); cho1.addItem("Q=1/3");
    add(b1); add(cho1);
    b1.addActionListener(this);
    setBackground(new Color(211, 211, 211));           // Light Gray Background
    cho1.setBackground(getBackground());
  }

  public void paint(Graphics g) {                      // Paint
    int x1, y1, x2, y2; int n=1000;
    double rq, phi, s, dt, x, v, dv;
    String z="Underdamped";
    if (kk==0) {
      b1.setBounds(75, 5, 55, 20);
      cho1.setBounds(5, 5, 60, 20); kk=1;
    }
    rq=1+cho1.getSelectedIndex(); dt=.01;
    g.setColor(Color.black);
    g.drawRect(0, 0, 400, 400); g.drawLine(0, 200, 400, 200);
    g.drawLine(200, 0, 200, 400);
    g.setColor(Color.red); g.drawArc(20, 20, 360, 360, 0, 360);
    if (kk==2) {                                       
      g.setColor(Color.blue);
      for (int j=0; j<=35; j=j+1) {
        phi=j*Math.PI/18; x=Math.cos(phi); v=Math.sin(phi);
        x1=200+(int)(180*x); y1=200-(int)(180*v);
        dv=-(rq*v+x)*dt; v=v+dv/2;                     // Feynman half-step
        for (int i=1; i<=n; i=i+1) {                   // Feynman loop  
          x=x+v*dt; dv=-(rq*(v+dv/2)+x)*dt; v=v+dv;
          x2=200+(int)(180*x); y2=200-(int)(180*(v-dv/2));
          g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
        }
      }
      if (rq==2) {
        g.setColor(Color.green); g.drawLine(0, 0, 400, 400);
        z="Critically Damped";
      }
      if (rq==3) {
        s=(3+Math.sqrt(5))/2;
        x1=200-(int)(200/s); y1=0;
        x2=200+(int)(200/s); y2=400;
        g.setColor(Color.green); g.drawLine(x1, y1, x2, y2);
        z="Overdamped";
      }
      g.setColor(Color.black); g.drawString(z, 275, 18); kk=1;
    }
  }

  public void actionPerformed(ActionEvent e) {
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) { kk=2; }
    repaint();
  }
}