function ImageExpander(oThumb, sImgSrc)
{
    // store thumbnail image and overwrite its onclick handler.
    this.oThumb = oThumb;
    this.oThumb.expander = this;
    this.oThumb.onclick = function() { this.expander.expand(); }
    
    // record original size
    this.smallWidth = oThumb.offsetWidth;
    this.smallHeight = oThumb.offsetHeight;    

    this.bExpand = true;
    this.bTicks = false;
    
    // self organized list
    if ( !window.aImageExpanders )
    {
        window.aImageExpanders = new Array();
    }
    window.aImageExpanders.push(this);

    // create the full sized image.
    this.oImg = new Image();
    this.oImg.expander = this;
    this.oImg.onload = function(){this.expander.onload();}
    this.oImg.src = sImgSrc;
}

ImageExpander.prototype.onload = function()
{
    this.oDiv = document.createElement("div");
    document.body.appendChild(this.oDiv);
    this.oDiv.appendChild(this.oImg);
    this.oDiv.style.position = "absolute";
    this.oDiv.expander = this;
    this.oDiv.onclick = function() {this.expander.toggle();};
    this.oImg.title = "Click to reduce";
    this.bigWidth = this.oImg.width;
    this.bigHeight = this.oImg.height;
    
    if ( this.bExpand )
    {
        this.expand();
    }
    else
    {
        this.oDiv.style.visibility = "hidden";
        this.oImg.style.visibility = "hidden";
    }
}
ImageExpander.prototype.toggle = function()
{
    // TODO: Remove
    /*
    var cw = document.body.clientWidth;
    var ch = document.body.clientHeight;
    var cx = document.body.scrollLeft + cw / 2;
    var cy = document.body.scrollTop + ch / 2;
    alert('cw:'+cw+' ch:'+ch+' cx:'+cx+' cy:'+cy);*/
    
    this.bExpand = !this.bExpand;
    if ( this.bExpand )
    {
        for ( var i in window.aImageExpanders )
            if ( window.aImageExpanders[i] !== this )
                window.aImageExpanders[i].reduce();
    }
}
ImageExpander.prototype.expand = function()
{
    // set direction of expansion.
    this.bExpand = true;

    // set all other images to reduce
    for ( var i in window.aImageExpanders )
        if ( window.aImageExpanders[i] !== this )
            window.aImageExpanders[i].reduce();

    // if not loaded, don't continue just yet
    if ( !this.oDiv ) return;
    
    // hide the thumbnail
    this.oThumb.style.visibility = "hidden";
    
    // calculate initial dimensions
    af = this.oThumb;
    this.x = this.oThumb.offsetLeft;
    this.y = this.oThumb.offsetTop;
    while (af.offsetParent) {
        af = af.offsetParent;
        this.x += af.offsetLeft;
        this.y += af.offsetTop;
    }
    this.w = this.oThumb.clientWidth;
    this.h = this.oThumb.clientHeight;
    
    this.oDiv.style.left = this.x + "px";
    this.oDiv.style.top = this.y + "px";
    this.oImg.style.width = this.w + "px";
    this.oImg.style.height = this.h + "px";
    this.oDiv.style.visibility = "visible";
    this.oImg.style.visibility = "visible";
    
    // start the animation engine.
    if ( !this.bTicks )
    {
        this.bTicks = true;
        var pThis = this;
        window.setTimeout(function(){pThis.tick();},25);    
    }
}
ImageExpander.prototype.reduce = function()
{
    // set direction of expansion.
    this.bExpand = false;
}
ImageExpander.prototype.tick = function()
{
    // calculate screen dimensions
    var cw;
    var ch;
    if (document.documentElement.clientHeight) {
        cw = document.documentElement.clientWidth;
        ch = document.documentElement.clientHeight;
    } else {
        cw = document.body.clientWidth;
        ch = document.body.clientHeight;
    }
    var cx;
    var cy;
    if (document.body.scrollLeft) {
        cx = document.body.scrollLeft + cw / 2;
        cy = document.body.scrollTop + ch / 2;
    } else {
        cx = document.documentElement.scrollLeft + cw / 2;
        cy = document.documentElement.scrollTop + ch / 2;
    }

    // calculate target
    var tw,th,tx,ty;
    if ( this.bExpand )
    {
        tw = this.bigWidth;
        th = this.bigHeight;
        if ( tw > cw )
        {
            th *= cw / tw;
            tw = cw;
        }    
        if ( th > ch )
        {
            tw *= ch / th;
            th = ch;
        }
        tx = cx - tw / 2;
        ty = cy - th / 2; 
    }
    else
    {
        tw = this.smallWidth;
        th = this.smallHeight;

        af = this.oThumb;
        tx = this.oThumb.offsetLeft;
        ty = this.oThumb.offsetTop;
        while (af.offsetParent) {
            af = af.offsetParent;
            tx += af.offsetLeft;
            ty += af.offsetTop;
        }
    }    
    // move 5% closer to target
    var nHit = 0;
    var fMove = function(n,tn) 
    {
        var dn = tn - n;
        if ( Math.abs(dn) < 3 )
        {
            nHit++;
            return tn;
        }
        else
        {
            return n + dn / 10;
        }
    }
    this.x = fMove(this.x, tx);
    this.y = fMove(this.y, ty);
    this.w = fMove(this.w, tw);
    this.h = fMove(this.h, th);
    
    this.oDiv.style.left = this.x + "px";
    this.oDiv.style.top = this.y + "px";
    this.oImg.style.width = this.w + "px";
    this.oImg.style.height = this.h + "px";

    // if reducing and size/position is a match, stop the tick    
    if ( !this.bExpand && (nHit == 4) )
    {
        this.oImg.style.visibility = "hidden";
        this.oDiv.style.visibility = "hidden";
        this.oThumb.style.visibility = "visible";

        this.bTicks = false;
    }
    
    if ( this.bTicks )
    {
        var pThis = this;
        window.setTimeout(function(){pThis.tick();},25);
    }
}