// Animated Bats elastic trail around the cursor
// LANGUAGE="JavaScript1.3"
//
// This seems most compatible when included at the end of the body of the HTML.
// just before the closing </BODY>.
// This insures that the window.document.body object exists, which we need to access.


/*
Elastic Trail script (By Philip Winston @ pwinston@yahoo.com, URL:http://members.xoom.com/ebullets)
Script featured on Dynamicdrive.com
For this and 100's more DHTML scripts, visit http://dynamicdrive.com
*/

// Thanks to Troels Jakobsen <tjak@get2net.dk>
// for fix which makes it work when the page is scrolled


if (1) //if (document.images)
{
  var nDots = 4;
  if (document.all&&window.print)
    document.body.style.cssText="overflow-x:hidden;overflow-y:scroll"

  var Xpos = 0;
  var Ypos = 0;

  var DELTAT = .01;                 // fixed time step, no relation to real time
  var SEGLEN = 10;                  // size of one spring in pixels
  var SPRINGK = 10;                 // spring constant, stiffness of springs
  // all the physics is bogus, just picked stuff to make it look okay
  var MASS = 1;
  var GRAVITY = 50;
  var RESISTANCE = 10;
  // stopping criterea to prevent endless jittering
  // doesn't work when sitting on bottom since floor
  // doesn't push back so acceleration always as big
  // as gravity
  var STOPVEL = 0.1;
  var STOPACC = 0.1;
  var DOTSIZE = 11;
  var BOUNCE = 0.75;                // BOUNCE is percent of velocity retained when bouncing off a wall

  var isNetscape = navigator.appName=="Netscape";

  // always on for now, could be played with to
  // let dots fall to botton, get thrown, etc.
  var followmouse = true;

  var dots = new Array();

  function InitAnimatedBats()
  {
    var i = 0;
    for (i = 0; i < nDots; i++)
    {
        dots[i] = new dot(i);
    }
    
    if (!isNetscape)
    {
        // I only know how to read the locations of the 
        // <LI> items in IE
        //skip this for now
        // setInitPositions(dots)
    }
    
    // set their positions
    for (i = 0; i < nDots; i++)
    {
        dots[i].obj.left = dots[i].X;
        dots[i].obj.top = dots[i].Y;
    }
    
    if (isNetscape)
    {
        // start right away since they are positioned
        // at 0, 0
        startanimate();
    }
    else
    {
        // let dots sit there for a few seconds
        // since they're hiding on the real bullets
        setTimeout("startanimate()", 2000);
    }
  } // InitAnimatedBats()

  function dot(i) 
  {
    this.X = Xpos;
    this.Y = Ypos;
    this.dx = 0;
    this.dy = 0;
    if (isNetscape)
    {	
        this.obj = eval("document.dot" + i);
    }
    else
    {
        this.obj = eval("dot" + i + ".style");
    }
  } // dot()

  function startanimate()
  {	
    setInterval("animate()", 20);
  }

  // This is to line up the bullets with actual LI tags on the page
  // Had to add -DOTSIZE to X and 2*DOTSIZE to Y for IE 5, not sure why
  // Still doesn't work great
  function setInitPositions(dots)
  {
    // initialize dot positions to be on top 
    // of the bullets in the <ul>
    var startloc = document.all.tags("LI");
    var i = 0;
    for (i = 0; i < startloc.length && i < (nDots - 1); i++)
    {
        dots[i+1].X = startloc[i].offsetLeft
            startloc[i].offsetParent.offsetLeft - DOTSIZE;
        dots[i+1].Y = startloc[i].offsetTop +
            startloc[i].offsetParent.offsetTop + 2*DOTSIZE;
    }
    // put 0th dot above 1st (it is hidden)
    dots[0].X = dots[1].X;
    dots[0].Y = dots[1].Y - SEGLEN;
  } // setInitPositions()

  // just save mouse position for animate() to use
  function MoveHandlerNS(e)
  {
    Xpos = e.pageX;
    Ypos = e.pageY;	  
    return true;
  } // MoveHandlerNS()

  // just save mouse position for animate() to use
  function MoveHandlerIE()
  {
    Xpos = window.event.x + document.body.scrollLeft;
    Ypos = window.event.y + document.body.scrollTop;	  
  } // MoveHandlerIE()

  if (isNetscape)
  {
    document.captureEvents(Event.MOUSEMOVE);
    document.onMouseMove = MoveHandlerNS;
  }
  else
  {
    document.onmousemove = MoveHandlerIE;
  }

  function vec(X, Y)
  {
    this.X = X;
    this.Y = Y;
  } // vec()

  // adds force in X and Y to spring for dot[i] on dot[j]
  function springForce(i, j, spring)
  {
    var dx = (dots[i].X - dots[j].X);
    var dy = (dots[i].Y - dots[j].Y);
    var len = Math.sqrt(dx*dx + dy*dy);
    if (len > SEGLEN) {
        var springF = SPRINGK * (len - SEGLEN);
        spring.X += (dx / len) * springF;
        spring.Y += (dy / len) * springF;
    }
  } // springForce()

  function animate()
  {	
    // dots[0] follows the mouse,
    // though no dot is drawn there
    var start = 0;
    if (followmouse)
    {
        dots[0].X = Xpos;
        dots[0].Y = Ypos;	
        start = 1;
    }
    
    for (i = start ; i < nDots; i++ )
    {
        var spring = new vec(0, 0);
        if (i > 0)
        {
            springForce(i-1, i, spring);
        }
        if (i < (nDots - 1))
        {
            springForce(i+1, i, spring);
        }
        
        // air resisitance/friction
        var resist = new vec(-dots[i].dx * RESISTANCE,
            -dots[i].dy * RESISTANCE);
        
        // compute new accel, including gravity
        var accel = new vec((spring.X + resist.X)/ MASS,
            (spring.Y + resist.Y)/ MASS + GRAVITY);
        
        // compute new velocity
        dots[i].dx += (DELTAT * accel.X);
        dots[i].dy += (DELTAT * accel.Y);
        
        // stop dead so it doesn't jitter when nearly still
        if (Math.abs(dots[i].dx) < STOPVEL &&
            Math.abs(dots[i].dy) < STOPVEL &&
            Math.abs(accel.X) < STOPACC &&
            Math.abs(accel.Y) < STOPACC)
        {
            dots[i].dx = 0;
            dots[i].dy = 0;
        }
        
        // move to new position
        dots[i].X += dots[i].dx;
        dots[i].Y += dots[i].dy;
        
        // get size of window
        var height, width;
        if (isNetscape)
        {
            height = window.innerHeight + document.scrollTop;
            width = window.innerWidth + document.scrollLeft;
        }
        else
        {	
            height = window.document.body.clientHeight + document.body.scrollTop;
            width = window.document.body.clientWidth + document.body.scrollLeft;
        }
        
        // bounce of 3 walls (leave ceiling open)
        if (dots[i].Y >=  height - DOTSIZE - 1)
        {
            if (dots[i].dy > 0)
            {
                dots[i].dy = BOUNCE * -dots[i].dy;
            }
            dots[i].Y = height - DOTSIZE - 1;
        }
        if (dots[i].X >= width - DOTSIZE)
        {
            if (dots[i].dx > 0)
            {
                dots[i].dx = BOUNCE * -dots[i].dx;
            }
            dots[i].X = width - DOTSIZE - 1;
        }
        if (dots[i].X < 0)
        {
            if (dots[i].dx < 0)
            {
                dots[i].dx = BOUNCE * -dots[i].dx;
            }
            dots[i].X = 0;
        }
        
        // move img to new position
        dots[i].obj.left = dots[i].X;			
        dots[i].obj.top =  dots[i].Y;		
    } // for (i = start ; i < nDots; i++ )
  } // animate()

  function StartCursorBats()
  {
    // Add the DIV tags for the individual bat layers.
    BatInvocation = "";
    // Netscape 4.7 refuses to dynamically reposition the first DIV tag, so we provide a hidden sacrifical DIV tag.
    BatInvocation = BatInvocation + '<div id="dot0" style="position: absolute; visibility: hidden; height: 1; width: 1;"></div>';
    BatInvocation = BatInvocation + '<div id="dot1" style="position: absolute; height: 11; width: 11;"><img src="../common/jcb_TrailBat.gif"></div>';
    BatInvocation = BatInvocation + '<div id="dot2" style="position: absolute; height: 11; width: 11;"><img src="../common/jcb_TrailBat.gif"></div>';
    BatInvocation = BatInvocation + '<div id="dot3" style="position: absolute; height: 11; width: 11;"><img src="../common/jcb_TrailBat.gif"></div>';
    document.write(BatInvocation);

    // Start it up...
    InitAnimatedBats();
  } // StartCursorBats()
} // if (document.images)