/*
Elastic Trail script (By Philip Winston @ pwinston@yahoo.com, URL: http://www.geocities.com/pwinston/)
Script featured on Dynamicdrive.com
For this and 100's more DHTML scripts, visit http://dynamicdrive.com
Updated by jscheuer1 in http://dynamicdrive.com/forums for modern Mozilla and Opera8
Originally and still good in IE4+ early Netscape
*/

var nDots = 5;

var Xpos = 0;
var Ypos = 0;

  // fixed time step, no relation to real time
var DELTAT = .01;
  // size of one spring in pixels
var SEGLEN = 10;
  // spring constant, stiffness of springs
var SPRINGK = 10;
  // all the physics is bogus, just picked stuff to
  // make it look okay
var MASS = 1;
// Positive XGRAVITY pulls right, negative pulls left
// Positive YGRAVITY pulls down, negative up
var XGRAVITY = 0;
var YGRAVITY = 50;
// RESISTANCE determines a slowing force proportional to velocity
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;
  // BOUNCE is percent of velocity retained when 
  // bouncing off a wall
var BOUNCE = 0.75;

/////////////////Stop Editing the Script///////////////

function iecompattest(){
	
return (document.compatMode && document.compatMode.indexOf("CSS")!=-1)? document.documentElement : document.body
}

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


var dots = new Array();

    for (i = 0; i < nDots; i++)
        dots[i] = new dot(i);    
    
    // set their positions
    for (i = 0; i < nDots; i++) {
        dots[i].obj.left = dots[i].X;
        dots[i].obj.top = dots[i].Y;
    }
        setInterval("animate()", 20);



function dot(i) 
{
    this.X = Xpos;
    this.Y = Ypos;
    this.dx = 0;
    this.dy = 0;
    if ((isNetscape)&&(!document.getElementById)) 	
       this.obj = eval("document.dot" + i);
    else if (document.all)
       this.obj = document.all['dot' + i].style;
    else if (document.getElementById)
       this.obj = document.getElementById('dot' + i).style;
    else
    return;
}


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

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

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


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

// 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;
    }
}


function animate() {	
    // dots[0] follows the mouse,
    // though no dot is drawn there
    var start = 0;
        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 + XGRAVITY,
            (spring.Y + resist.Y)/ MASS + YGRAVITY);
        
        // 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 + window.pageYOffset;
            width = window.innerWidth + window.pageXOffset;
        } else {	
            height = iecompattest().clientHeight + iecompattest().scrollTop-8;
            width = iecompattest().clientWidth + iecompattest().scrollLeft;
        }
        
        // bounce off 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;		
    }
}