jQuery zoom

<!-- Lets make a simple image magnifier -->
<div class="magnify">
    
    <!-- This is the magnifying glass which will contain the original/large version -->
    <div class="large"></div>
    
    <!-- This is the small image -->
    <img class="small" src="http://thecodeplayer.com/uploads/media/iphone.jpg" width="200"/>
    
</div>

<!-- Lets load up prefixfree to handle CSS3 vendor prefixes -->
<script src="http://thecodeplayer.com/uploads/js/prefixfree.js" type="text/javascript"></script>
<!-- You can download it from http://leaverou.github.com/prefixfree/ -->

<!-- Time for jquery action -->
<script src="http://thecodeplayer.com/uploads/js/jquery-1.7.1.min.js" type="text/javascript"></script>

$(document).ready(function(){

    var native_width = 0;
    var native_height = 0;

    //Now the mousemove function
    $(".magnify").mousemove(function(e){
        //When the user hovers on the image, the script will first calculate
        //the native dimensions if they don't exist. Only after the native dimensions
        //are available, the script will show the zoomed version.
        if(!native_width && !native_height)
        {
            //This will create a new image object with the same image as that in .small
            //We cannot directly get the dimensions from .small because of the 
            //width specified to 200px in the html. To get the actual dimensions we have
            //created this image object.
            var image_object = new Image();
            image_object.src = $(".small").attr("src");
            
            //This code is wrapped in the .load function which is important.
            //width and height of the object would return 0 if accessed before 
            //the image gets loaded.
            native_width = image_object.width;
            native_height = image_object.height;
        }
        else
        {
            //x/y coordinates of the mouse
            //This is the position of .magnify with respect to the document.
            var magnify_offset = $(this).offset();
            //We will deduct the positions of .magnify from the mouse positions with
            //respect to the document to get the mouse positions with respect to the 
            //container(.magnify)
            var mx = e.pageX - magnify_offset.left;
            var my = e.pageY - magnify_offset.top;
            
            //Finally the code to fade out the glass if the mouse is outside the container
            if(mx < $(this).width() && my < $(this).height() && mx > 0 && my > 0)
            {
                $(".large").fadeIn(100);
            }
            else
            {
                $(".large").fadeOut(100);
            }
            if($(".large").is(":visible"))
            {
                //The background position of .large will be changed according to the position
                //of the mouse over the .small image. So we will get the ratio of the pixel
                //under the mouse pointer with respect to the image and use that to position the 
                //large image inside the magnifying glass
                var rx = Math.round(mx/$(".small").width()*native_width - $(".large").width()/2)*-1;
                var ry = Math.round(my/$(".small").height()*native_height - $(".large").height()/2)*-1;
                var bgp = rx + "px " + ry + "px";
                
                //Time to move the magnifying glass with the mouse
                var px = mx - $(".large").width()/2;
                var py = my - $(".large").height()/2;
                //Now the glass moves with the mouse
                //The logic is to deduct half of the glass's width and height from the 
                //mouse coordinates to place it with its center at the mouse coordinates
                
                //If you hover on the image now, you should see the magnifying glass in action
                $(".large").css({left: px, top: py, backgroundPosition: bgp});
            }
        }
    })
})