// You may study, use, modify, and distribute this example for any purpose.
// This example is provided WITHOUT WARRANTY either expressed or implied.
// ALso: this is NOT a sample of good Java OO style, it is just
// a FORTRAN IV program written in Java.

import java.applet.*;    // Don't forget these import statements!
import java.awt.*;
import java.lang.Math;
/** Displays a mathematical curve called an Henrici Spiral
*/
public class Henrici extends Applet {
	public void init() {
	}//init

    public void paint(Graphics g) {
	double v1,v2,t1,t2,d,u1,u2;
	int n=5000;

	double t, a1, a2, r1, r2;
	double c1,c2,s1,s2;
	double x1,x2,y1,y2;

	d=1;
	v1=20;u1=.01; t1=.5;
	v2=150;u2=.05; t2=.17;

	g.setColor(Color.white);
	g.fillRect(1,1,399,399);

	x1=0; y1=0;
	g.setColor(Color.blue);
	for(int i=0; i<n; i++){
		if(i%2 == 0)
			g.setColor(Color.blue);
		else
			g.setColor(Color.red);

		t=d*i;
		a1=t*t1;
		a2=t*t2;
		c1=Math.cos(a1);
		s1=Math.sin(a1);
		c2=Math.cos(a2);
		s2=Math.sin(a2);
		r1=v1-u1*t;
		r2=v2-u2*t;
		x2=200+r1*c1+r2*c2;
		y2=200+r1*s1+r2*s2;
		
		if(i>0)g.drawLine((int)x1,(int)y1,(int)x2,(int)y2);
		x1=x2;
		y1=y2;
	}

     }//paint

/**When used as an application the main program
	creates the window in which the message is painted.
*/
    public static void main(String args[]) {
	Frame f = new Frame("Henrici Spiral");
	Henrici spiral = new Henrici();
	spiral.init();
	spiral.start();

	f.setBackground(Color.lightGray);
	f.setForeground(Color.blue);
	f.add("Center", spiral);
	f.setSize(400, 400);
	f.setVisible( true);
    }
}