// approach.java

import java.applet.Applet;
import java.applet.AppletContext;
import java.awt.*;
import java.awt.event.*;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Random;

public class approach extends Applet  implements Runnable
{
   class mml extends MouseMotionAdapter
   {  public void mouseMoved   (MouseEvent e)  {_msX=e.getX();  _msY=e.getY();}
      public void mouseDragged (MouseEvent e)  {_msX=e.getX();  _msY=e.getY();}
      mml ()  {}
   }

   class msl extends MouseAdapter
   {  public void mousePressed  (MouseEvent e) {_msX=e.getX();  _msY=e.getY();
                                                _msDn = true; }
      public void mouseReleased (MouseEvent e) {_msDn = false;}
      msl ()  {}
   }

   class g2
   {  public void clr (int r, int g, int b)
      {  _gfx.setColor (new Color (r, g, b));
         _gfx.fillRect (0, 0, _w, _h);
         for (_y = 0; _y < _h; _y++)  for (_x = 0; _x < _w; _x++)
            {_r[_x][_y] = r;  _g[_x][_y] = g;}
      }

      public void draw (double x, double y, int r, int g, int b, double f)
      {  if (x <= 0.0D || x >= (double)(_w-1) ||
             y <= 0.0D || y >= (double)(_h-1))  return;
        int    ix = (int)x,          jx = ix + 1;
        int    iy = (int)y,          jy = iy + 1;
        double dx = (double)jx - x,  ex = 1.0D - dx;
        double dy = (double)jy - y,  ey = 1.0D - dy;
        double f1;
         f1 = dx * dy * f;
         _r[ix][iy] = (int)(f1 * (double)r + (double)_r[ix][iy]);
         if (_r[ix][iy] > 255)  _r[ix][iy] = 255;
         _g[ix][iy] = (int)(f1 * (double)g + (double)_g[ix][iy]);
         if (_g[ix][iy] > 255)  _g[ix][iy] = 255;

         f1 = ex * dy * f;
         _r[jx][iy] = (int)(f1 * (double)r + (double)_r[jx][iy]);
         if (_r[jx][iy] > 255)  _r[jx][iy] = 255;
         _g[jx][iy] = (int)(f1 * (double)g + (double)_g[jx][iy]);
         if (_g[jx][iy] > 255)  _g[jx][iy] = 255;

         f1 = dx * ey * f;
         _r[ix][jy] = (int)(f1 * (double)r + (double)_r[ix][jy]);
         if (_r[ix][jy] > 255)  _r[ix][jy] = 255;
         _g[ix][jy] = (int)(f1 * (double)g + (double)_g[ix][jy]);
         if (_g[ix][jy] > 255)  _g[ix][jy] = 255;

         f1 = ex * ey * f;
         _r[jx][jy] = (int)(f1 * (double)r + (double)_r[jx][jy]);
         if (_r[jx][jy] > 255)  _r[jx][jy] = 255;
         _g[jx][jy] = (int)(f1 * (double)g + (double)_g[jx][jy]);
         if (_g[jx][jy] > 255)  _g[jx][jy] = 255;

         _gfx.setColor (new Color (_r[ix][iy], _g[ix][iy], 0));
         _gfx.drawLine (ix, iy, ix, iy);
         _gfx.setColor (new Color (_r[jx][iy], _g[jx][iy], 0));
         _gfx.drawLine (jx, iy, jx, iy);
         _gfx.setColor (new Color (_r[ix][jy], _g[ix][jy], 0));
         _gfx.drawLine (ix, jy, ix, jy);
         _gfx.setColor (new Color (_r[jx][jy], _g[jx][jy], 0));
         _gfx.drawLine (jx, jy, jx, jy);
      }

      protected int _r[][];
      protected int _g[][];
      protected int _w;
      protected int _h;
      protected int _x;
      protected int _y;

      public g2 (int w, int h)
      {  _w = w;  _h = h;  _r = new int[_w][_h];  _g = new int[_w][_h];  }
   }


   public approach ()
   {  _inited = false;  _msDn = false;  _msX = 0;  _msY = 0;  }

   public void init ()
   {  _w = getWidth ();  _h = getHeight ();
      _img = createImage (_w, _h);  _gfx = _img.getGraphics ();
      _inited = true;
      _g = new g2 (_w, _h);
      addMouseListener       (new msl ());
      addMouseMotionListener (new mml ());
   }

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

   public void update (Graphics g)  {paint (g);}
   public void paint  (Graphics g)  {if (_inited) g.drawImage (_img,0,0,this);}

   public void run ()
   { int ln = 30;
     int dt = 10;
     double x [] = new double[ln];
     double y [] = new double[ln];
     double xf[] = new double[ln];
     double yf[] = new double[ln];
      for (int n = 0; n < ln; n++)
         {x[n] = 0.0D;  y[n] = 0.0D;  xf[n] = 0.0D;  yf[n] = 0.0D;}
      _g.clr (0, 0, 0);
      while (true) {
         for (int n = 0; n < dt; n++)  for (int i = 0; i < ln; i++) {
           double dx = (double)_msX - x[i];
           double dy = (double)_msY - y[i];
            xf[i] += 0.01 * dx * (1.0 - (0.75 * (double)i) / (double)ln);
            xf[i] *= 0.995;
            yf[i] += 0.01 * dy * (1.0 - (0.75 * (double)i) / (double)ln);
            yf[i] *= 0.995;
            x [i] += 0.01 * xf[i];
            y [i] += 0.01 * yf[i];
            _g.draw (x[i], y[i], 255, 80, 0, 0.5);
         }
         if (_msDn) {
            _msDn = false;  _g.clr (0, 0, 0);
            dt = 3 + _msX * 18 / _w;   // dt betw 3 and 20 based on _msX
         }
         repaint ();
         try   {Thread.sleep (20L);}
         catch (InterruptedException interruptedexception)  {}
      }
   }

   Thread   _thr;
   Image    _img;
   Graphics _gfx;
   int      _w, _h;
   boolean  _msDn, _inited;
   int      _msX, _msY;
   g2       _g;
}