//--------------------------------------------------------------------------
//  star field simulator	  Version 1.1
//
//  (C)  COPYRIGHT International Business Machines Corp. 1996 
//
//  by John Henckel, henckel@vnet.ibm.com              Aug 1996
//
//  This is a little java program that simulates flying through a field of
//  stars.  Have fun with it!
//
//  If you have any comments about this, or if you make any modifications
//  to the program, please send me a note.
//
//---------------------------------------------------------------------------
//  Permission to use, copy, modify, distribute and sell this software
//  and its documentation for any purpose is hereby granted without fee,
//  provided that the above copyright notice appear in all copies and
//  that both that copyright notice and this permission notice appear
//  in supporting documentation.
//
//  This program has not been thoroughly tested under all conditions.  IBM,
//  therefore, cannot guarantee or imply reliability, serviceability, or
//  function of this program.  The Program contained herein is provided
//  'AS IS'.  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
//  PARTICULAR PURPOSE ARE EXPRESSLY DISCLAIMED.
//  IBM shall not be liable for any lost revenue, lost profits or other
//  consequential damages caused by the Program even if advised of the
//  possibility of such damages.  Furthermore, IBM shall not be liable for
//  any delays, losses or any other damages which may result from
//  furnishing the Program, even if advised of the possibility of such
//  damages.

import java.awt.*;

//-------------------------------------------------------------------
//  This is the main applet class

public class stars extends java.applet.Applet implements Runnable {
  Thread t;
  int num,shading;
  float color, speed, wander;
  boolean hyper,dbuf;
  star[] s;
  int xm,ym;      // middle of canvas
  Image img;		// used for dbuf
  Graphics g2;		// used for dbuf

  public void init() {
    String st;
    color = 0.3F;
    speed = 1.0F;
    wander = 1.0F;
    num = 50;
    shading = 8;
    st = getParameter("dbuf");     dbuf = st==null || st.equals("yes");
    st = getParameter("hyper");    hyper = st!=null && !st.equals("no");
    st = getParameter("speed");
    if (st!=null) speed = Float.valueOf(st).floatValue();
    st = getParameter("wander");
    if (st!=null) wander = Float.valueOf(st).floatValue();
    st = getParameter("color");
    if (st!=null) color = Float.valueOf(st).floatValue();
    st = getParameter("num");
    if (st!=null) num = Integer.valueOf(st).intValue();
    st = getParameter("shading");
    if (st!=null) shading = Integer.valueOf(st).intValue();
    if (color<0 || color>1) color = 0.0F;
    if (wander>10) wander = 10F;        // max wander
    wander /= 1000;
    if (speed>10) speed = 10F;        // max speed
    speed /= 100;
    if (num<1) num=1;
    s = new star[num];
    for (int i=0; i<num; ++i)
      s[i] = new star();
  }
  public void start() {
    if (t==null) {
      t = new Thread(this);
      t.start();	  // start new thread
    }
  }
  public void stop() {
    if (t!=null) {
      t.stop();	  // kill the thread
      t = null;	  // release object
    }
  }
  public void run() {
    setBackground(Color.black);
    while (true) {
      xm = size().width/2;
      ym = size().height/2;
      repaint();
      Thread.yield();
    }
  }
  public void paint(Graphics g) {
    int x,y;
    double p;
    double sx,sy,sz,r;
    float h;
    
    for (int i=0; i<num; ++i) {
      if (i>=num) i-=num;
      if (s[i].move(speed,wander))
	s[i].reset(xm,ym);
      sx = s[i].x;
      sy = s[i].y;
      sz = s[i].z;
      h = s[i].h;
      x = (int)(sx / sz);
      y = (int)(sy / sz);
      if (x > xm || x < -xm || y > ym || y < -ym) 
	s[i].reset(xm,ym);
      r = 0.3 / (sz*sz + 0.003);       // note 0.3 < r < 100
      if (r > shading) {
	r *= 1.33;
	for (int j=0; j<r; ++j) {        // draw shaded ball
	  g.setColor(Color.getHSBColor(h,color,(float)Math.sqrt(1 - j*j/(r*r))));
	  g.drawOval(xm + x - j/2,ym + y - j/2,j,j);
	}
      }
      else if (r > 3.4) {          // simple disk
	int j = (int)r;
	g.setColor(Color.getHSBColor(h,color,1.0F));
	g.fillOval(xm + x - j/2,ym + y - j/2,j+1,j+1);
      }
      else if (r > 1) {          // simple box
	g.setColor(Color.getHSBColor(h,color,1.0F));
	g.fillRect(xm + x,ym + y,(int)(r+0.9),(int)(r+0.4));
      }
      else {         // simple dot
	x += xm; y += ym;
	g.setColor(Color.getHSBColor(h,color,(float)r));
	g.drawLine(x,y,x,y);
      }
    }
  }
  public void update(Graphics g) {
    if (hyper) paint(g);
    else if (dbuf) {           // double buffering
      if (img==null) {
	img = createImage(size().width,size().height);
	g2 = img.getGraphics();
      }
      g2.setColor(Color.black);
      g2.fillRect(0,0,size().width,size().height); // this is because of a bug in Netscape
      paint(g2);
      g.drawImage(img,0,0,this);
    }
    else super.update(g);
  }
  public static void main(String args[]) {
    stars app = new stars();
    app.init();
    app.run();
  }
}

class star {
  double x,y,z;	 // location
  double vx,vy,ax,ay;  // velocity and acceleration
  float h;       // hue
  static Random rand = new Random();
  star() { z=0; }
  star(double zz) { z=zz; }
  void reset(int mx, int my) {
    x = Math.random()*2*mx - mx;
    y = Math.random()*2*my - my;
    z = 1.0;
    vx=vy=ax=ay=0.0;
    h = (float)Math.random();
  }
  boolean move(float spd,float wan) {
    if (wan>0) {
      ax += (Math.random()-0.5)*wan;
      ay += (Math.random()-0.5)*wan;
      vx += ax; vy += ay;
      x += vx; y += vy;
    }
    return (z-=spd)< 2*spd;         // min distance
  }
}