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

public class SpreadOfStimulus extends Applet implements Runnable,MouseListener,MouseMotionListener {
	Image offscreen;
	Graphics g;
	boolean[][] map,trace;
	boolean spreading=false;
	
	public void init() {
		setBackground(Color.white);
		
		offscreen=createImage(256,256);
		g=offscreen.getGraphics();
		
		addMouseListener(this);
		addMouseMotionListener(this);
		
		map=new boolean[64][64];
		trace=new boolean[64][64];
		for (int x=0;x<64;x++)
			for (int y=0;y<64;y++) {
				map[x][y]=false;
				trace[x][y]=false;
			}
		
	}

	public synchronized void run() {
		while(spreading) {
			boolean[][] offspring=new boolean[64][64];
			for (int x=0;x<64;x++)
				for (int y=0;y<64;y++) {
					if (map[x][y])
						g.setColor(Color.black);
					else if (trace[x][y])
						g.setColor(Color.gray);
					else
						g.setColor(Color.white);
					g.fillRect(x*4,y*4,4,4);
					offspring[x][y]=(
						!map[x][y] && !trace[x][y] &&
						(map[(x+63)%64][y] || map[(x+1)%64][y] 
						|| map[x][(y+63)%64] || map[x][(y+1)%64])
					);
				}
			trace=map;
			map=offspring;
			repaint();
			try {
				Thread.sleep(100);
			} catch (InterruptedException e) {
			}
		}
	}
	
	public void update(Graphics g) {
		g.drawImage(offscreen,0,0,this);
	}
	
	public void mouseClicked(MouseEvent e) {}
	public void mouseEntered(MouseEvent e) {}
	public void mouseExited(MouseEvent e) {}
	public void mousePressed(MouseEvent e) {
		spreading=false;
		try {
			map[e.getX()/4][e.getY()/4]=true;
		} catch (ArrayIndexOutOfBoundsException ex) {
		}
	}
	public void mouseReleased(MouseEvent e) {
		synchronized(this) {
			spreading=true;
			new Thread(this).start();
		}
	}
	public void mouseDragged(MouseEvent e) {
		try {
			map[e.getX()/4][e.getY()/4]=true;
		} catch (ArrayIndexOutOfBoundsException ex) {
		}
	}
	public void mouseMoved(MouseEvent e) {}
}