// Spiral.java  expanding and contracting spirals

import java.awt.*;
import java.awt.event.*;

public class Spiral extends Frame
{
  int height = 500;
  int width = 500;
  Spiral()
  {
    setTitle("Spiral");
    setSize(width,height);
    setBackground(Color.white);
    setForeground(Color.black);
    addWindowListener(new WindowAdapter()
    {
      public void windowClosing(WindowEvent e)
      {
        System.exit(0);
      }
    });
    setVisible(true);
  }

  public void paint(Graphics g)
  {
    double dt = 0.1;
    double x1, x2, y1, y2, r, c;
    int xm = width/2;
    int ym = height/2;

    // draw text
    g.setColor(Color.red);
    g.drawString("r = c*t", 20, 50);
    g.drawString("x1 = r*Math.cos(t)", 20, 70);
    g.drawString("y1 = r*Math.sin(t)", 20, 90);

    c = 5.0;
    for(double  t=10.0; t<30.0; t=t+dt)
    {
      r = c*t;
      x1 = r*Math.cos(t);
      y1 = r*Math.sin(t);
      r = c*(t+dt);
      x2 = r*Math.cos(t+dt);
      y2 = r*Math.sin(t+dt);
      g.drawLine((int)x1+xm, (int)y1+ym, (int)x2+xm, (int)y2+ym);
    }

    g.setColor(Color.blue);
    g.drawString("r = c/t", width/2, 50);
    g.drawString("x1 = r*Math.cos(t)", width/2, 70);
    g.drawString("y1 = r*Math.sin(t)", width/2, 90);

    c = 400.0;
    for(double t=10.0; t<30.0; t=t+dt)
    {
      r = c/t;
      x1 = r*Math.cos(t);
      y1 = r*Math.sin(t);
      r = c/(t+dt);
      x2 = r*Math.cos(t+dt);
      y2 = r*Math.sin(t+dt);
      g.drawLine((int)x1+xm, (int)y1+ym, (int)x2+xm, (int)y2+ym);
    }
  }

  public static void main(String args[])
  {
    new Spiral();
  }
} // end Spiral.java