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

public class starsim extends Applet implements Runnable
{
	int STARS = 200;

	int[] x, y, xv, xi;
	Color c[];

	Thread runner;
	
	// Double Buffer variables
	Image DB_Image;
    Graphics DB_Graphics;
	Dimension DB_Dimension;
		
	public void init(){
		int i, t;	
		String p;
		p = getParameter("stars");
		if (p == null) p = "200";
		STARS = Integer.valueOf(p).intValue();
		if (STARS == 0 || STARS > 200 || STARS < 1) STARS=200;

		x  = new int[STARS];
		y  = new int[STARS]; 
		xv = new int[STARS];
		xi = new int[STARS];
		c  = new Color[STARS];

		DB_Dimension = size();

        if (DB_Graphics == null) {
			DB_Image = createImage(DB_Dimension.width, DB_Dimension.height);
			DB_Graphics = DB_Image.getGraphics();
		}

		setBackground(Color.black);
		for(i=0;i<STARS;i++){
			x[i] = (int)(Math.random()*DB_Dimension.width);
			y[i] = (int)(Math.random()*DB_Dimension.height);
			xi[i] = x[i];

			while((t = (int)(Math.random()*30)) <0 || t>2){}
				  
			switch(t){
				case 0:{
					xv[i] = 2;
	                c[i] = Color.gray;
				} break;
				case 1:{
					xv[i] = 4;
	                c[i] = Color.lightGray;
				} break;
				case 2:{
					xv[i] = 6;
	                c[i] = Color.white;
				} break;
			} // END SWITCH
		} // END FOR INIT LOOP

	}

	public void paint(Graphics g){
		update(g);
	}
	
	public void update(Graphics g){		

		DB_Graphics.setColor(Color.black);
		DB_Graphics.fillRect(0, 0, DB_Dimension.width, DB_Dimension.height);		
		
		// Unrolled loop to speed up pixel plotting
		for(int i=0;i<STARS;i++){			
			DB_Graphics.setColor(c[i]);
			DB_Graphics.drawLine(x[i],y[i],x[i],y[i]);		

			DB_Graphics.setColor(c[++i]);
			DB_Graphics.drawLine(x[i],y[i],x[i],y[i]);
			
			DB_Graphics.setColor(c[++i]);
			DB_Graphics.drawLine(x[i],y[i],x[i],y[i]);		

			DB_Graphics.setColor(c[++i]);
			DB_Graphics.drawLine(x[i],y[i],x[i],y[i]);		

		}
		g.drawImage(DB_Image, 0, 0, this);
	}

	public void run(){
		int i, t;
		while(true){
		for (i=0; i<STARS; i++){
			if ((x[i]+=xv[i])>=DB_Dimension.width) {
				x[i] = 0;
				t=4;
				while((t = (int)(Math.random()*30)) <0 || t>2){}
				switch(t){
					case 0:{
						xv[i] = 2;
						c[i] = Color.gray;
					} break;
					case 1:{
						xv[i] = 4;
						c[i] = Color.lightGray;
					} break;
					case 2:{
						xv[i] = 6;
	                c[i] = Color.white;
					} break;
				} // END SWITCH
			} // END IF
		} // END FOR INDEX LOOP

	    try{
			Thread.sleep(50);
		} catch(InterruptedException e) {stop();}
			repaint();
		}
	}
	
/* 
 * This is optional thread suspention code, it suspends the applet when the mouse enters
 * the applet region 
*/ 

/*
	public boolean mouseEnter(Event evt, int x, int y) {
		try	{
			runner.suspend(); 
		}	catch (InterruptedException e){stop();}
        return true;
	}
	
	public boolean mouseExit(Event evt, int x, int y) {
		try	{
			runner.resume(); 
		}	catch (InterruptedException e){runner.start();}	
		return true;
	}
/* */
	public void start() {
		if (runner == null); { 
			runner = new Thread(this); 
			runner.start(); 
		} 
	}

	public void stop() { 
		if (runner != null) {
		runner.stop(); 
		runner = null; 
		} 
	}

}