javascript - how to compute Facebook graph api cover offset_y to pixel?

Question

I can retrieve facebook cover source and offset_y from graph api for example -

https://graph.facebook.com/Inna

I get this -

"cover": {
      "cover_id": "10151356812150381",
      "source": "http://sphotos.xx.fbcdn.net/hphotos-snc7/s720x720/419277_10151356812150381_302056140380_23114100_97822830_n.jpg",
      "offset_y": 54
   }

But when i look at the actual facebook page for this, i see the top offset is -135px. How is that calculated from 54?

I want to display someones cover photo on my website, with the same offset as facebook. So I am basically doing -

<div class="ed-cover">
            <img src=""/>
    </div>

CSS -

.ed .ed-cover
{
    height:315px;
    overflow:hidden;
    position:relative;
}

.ed .ed-cover img
{
    width:100%;
    position:absolute;    
}

JS -

FB.api(artist, function (data) {
                        $('.ed-cover img').attr('src', data.cover.source).css("top", -1 * data.cover.offset_y);
                    });

But the CSS offset here for the "top" property is incorrect as i get back 54 and the real offset is -135px;

Answer 1

Does that really work for you? I have tested it with many images (landscape and portrait) and if you use %, the position is always slightly different. This here works good for me:

$.fn.positionate_cover = function (offset_y) {
    var cover_w = 850;
    var cover_h = 315;
    var img_w = $(this).width ();
    var img_h = $(this).height ();
    var real_img_h = (cover_w * img_h / img_w) - cover_h;

    $(this).css ({ top: parseInt (real_img_h * offset_y / 100 * -1) + "px" });
};

$(".ed-cover img")
    .attr ("src", data.cover.source)
    .positionate_cover (data.cover.offset_y)
;