// Illustration of a loop: the logarithmic spiral

import java.io.*;
import java.awt.*;

// Logarithmic spiral example
public class Spiral extends Frame {
  private final int hc= 300;   // Center of spiral 
  private final int vc= 250;   //   is (hc,vc)
  private final int n= 2000;   // Number of sides to draw
  private final double d= .2;  // Length of leg k is k*d
  private int turn= 120;       // The turn factor
 
  // Set the turn between successive lines to t
  public void setTurn(int t) {
     turn= t;
  }

  // The spiral consists of n line segments. Line segment 1
  // has starting point (hc, vc). Line segment k, for 1<=k<=n,
  // has length k*d. Each line segment makes an angle of turn
  // degrees with the previous line segment. The colors of the
  // lines alternate between red, blue, and green.

  public void paint(Graphics g) {
     int h= hc;
     int v= vc;
     int k= 1;
     //Invariant: legs 1..k-1 have been drawn, and leg k is
     //           to be drawn with start point (h,v)
     while (k<=n) {
        //Draw line k
            if (k%3==0) g.setColor(Color.red);
            if (k%3==1) g.setColor(Color.blue);
            if (k%3==2) g.setColor(Color.green);
		
            int theta= k*turn % 360;
            double L= k*d;
            // Calculate the end point (h_next,v_next) of
            // the line
               int h_next= (int) Math.round(
                     h+L*Math.cos(theta*Math.PI/180));
               int v_next= (int) Math.round(
                     v+L*Math.sin(theta*Math.PI/180));
            g.drawLine(h,v,h_next, v_next);
		    
        h= h_next; v= v_next;
        k= k+1;
     }
   }
}