Question

Exactly 50px, to be precise. I know it’s in the code somewhere, but I think i’ve been staring at it for too long.

Backstory: I’m making a simple jQuery plugin which will add a magnifying lens effect when hovering over images. It was working fine, then I added some code, and it started acting odd when entering from the top of the image. I used firebug to see if there was a difference between the top offset of the image and the pageY value of the cursor and there was.

In the link below you can see that moving in from above it doesn’t activate on time.

Code:

update: function(event) {
    img.stop(); // To stop the image from constantly animating
    img.lens.stop(); // Same for the lens
    img.lens.leftmax = img.width + img.left;
    img.lens.topmax = img.height + img.top;

    img.lens.x = event.pageX - (vars.size / 2);
    img.lens.y = event.pageY - (vars.size / 2);

    img.lens.css({
        left: img.lens.x + 'px',
        top: img.lens.y + 'px'
    });

    console.log(img.top + ' : ' + event.pageY);

    if (event.pageX >= img.lens.leftmax || event.pageY >= img.lens.topmax || event.pageX <= img.left || event.pageY <= img.top) {

        img.lens.hide(); // Hide lens
        if (options.caption) {
            img.lens.caption.hide();
        } // Hide Caption
        if (options.overlay) {
            methods.nooverlay();
        }

        // API Callback Exit
        vars.onexit(img, img.lens);
    } else {
        // API Callback on entering
        vars.onenter(img, img.lens);

        if (options.overlay) {
            methods.overlay();
        }

        methods.doMath(event); // Recalculate pos
        img.lens.show(); // Show lens
        img.lens.css({
            backgroundPosition: img.lens.bgleft + 'px ' + img.lens.bgtop + 'px'
        }); // Assign coordinates
        if (options.caption) {
            img.lens.caption.show(); // Show caption
            img.lens.caption.x = img.lens.x + ((vars.size - img.lens.caption.outerWidth()) / 2); // Center caption
            img.lens.caption.css({
                left: img.lens.caption.x + 'px',
                top: img.lens.y + vars.size + 'px'
            }); // Assign coordinates
        }
    }
},

doMath: function(event) {
    img.wr = img.Owidth / img.width;
    img.hr = img.Oheight / img.height;

    img.lens.bgleft = String(((event.pageX - img.left) * img.wr - vars.size / 2) * (-1));
    img.lens.bgtop = String(((event.pageY - img.top) * img.hr - vars.size / 2) * (-1));
},​

These are the main functions (part of a map) that make the hover action work and where i think the problem should lie. The code is pretty long, so for the sake of readability i’ll add a link to where i’m hosting the page in case you want to look at the full plugin code.

Link removed

Where am I going wrong?

EDIT:

So apparently the cause of the problem is a floating span element that is nested in a sibling of the parent, of the parent tag of the image:

    <div class="header">
        <!-- This span tag -->
        <span class="note">&rarr; If you're using IE8 or lower, you will see a square lens</span>
        <h1>jQuery Images Lens Preview</h1>
        <span><i>The most customizable zoom tool there is.</i> <a href="#">GET IT NOW!</a></span>
        <div style="clear: both;"></div>
   </div>

    <div class="example">
        <div class="desc">
             <h3>Demonstration #1 - Basic Usage</h3>
             <pre>$('img.basic').superLens();</pre>
        </div>
        <div class="theimages">
            <img src="images/demo_img1.jpg" width="214" height="320" class="basic" />
            <img src="images/demo_img2.jpg" width="214" height="320" class="basic" />
        </div>
        <div style="clear: both;"></div>
    </div>

Any idea why this is happening?

Answer 1

It doesn’t actually return a 50px difference.

Basically the img.top is the offset from the document to the top of the image. The event.pageY is the offset of the cursor to the top of the document, as the hover event is the exact point of the cursor, not the point of the hovered object.

If you want, you could use event.target and get the top value from that.