// Applet to simulate a Brownian path in a rectangle
// It's a polygonal path with random displacements

import java.awt.Graphics;
import java.awt.Polygon;
import java.awt.Color;
import java.awt.Component;
import java.lang.Math;
import java.util.Random;

public class BrownianApplet extends java.applet.Applet
        implements Runnable {

        
        int delta = 2;  // length of each step
        int cur_x = 100, cur_y = 100; // starting point
        Polygon path;
        Thread myThread;
        Random rng;
        int pause = 100; // time between steps in milliseconds

        // The init method is called when the applet starts

        public void init(){

        path = new Polygon();         // create an empty path
        rng = new Random();   
	setBackground(Color.red);
        }

        // The start method is called everytime the applet is (re)started
        // All this one does is begin a thread of execution

        public void start(){
                if(myThread == null){
                myThread = new Thread(this);
                myThread.start();
                }
        }

        public void stop(){
                if(myThread != null){
                        myThread.stop();
                        myThread = null;  // allow garbage collection
                }
        }

        public void run(){

        // Create Path
                 while(true){
                        int pmx,pmy;
                        pmx = ( rng.nextDouble() < 0.5 ? 1 : -1);
                        pmy = ( rng.nextDouble() < 0.5 ? 1 : -1);
                        path.addPoint(cur_x ,cur_y );
                        cur_x += pmx*delta;
                        cur_y += pmy*delta;
                        repaint();
                        try { Thread.sleep(1000);}
                        catch (InterruptedException e) {}
                }
        }

        public void paint(Graphics g){
               
                g.drawPolygon(path);    // draw path
        }
}