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Archive for the ‘HTML’ Category

Feb22

CSS & Javascript image preloader

CSS, HTML, Javascript, Web Development   No Comments

While building a photo gallery for a client I ran into an issue where the photos took too long to load and clicking thumbnails before all the photos loaded resulted in ugly transitions.

My solution was to put a semi-transparent “shield” (containing a loading animation) over the gallery. The user will be able to see the images loading, but will be unable to click anything until all images are loaded and the shield is hidden. Here’s the finished product.

Explanation follows the code.

Here’s the html. This goes inside the div that contains your gallery.

<div id="gallery_loader"> <!-- wrapper for shield -->
    <div></div> <!-- this is the actual shield -->
    <img src="animated_loader.gif"><!-- image preloader -->
</div>

…and the CSS:

#gallery_loader {
    position:absolute; /* Position the wrapper at the top left corner */
    top:0;
    left: 0;
    width:100%; /* cover the entire width of your gallery */
    height:100%; /* cover the entire height of your gallery */
    overflow:hidden; /* hide anything that might overflow */
    z-index:999; /* make sure the shield is on top over everything */
}
#gallery_loader div { /* the actual shield */
    position:absolute; /* Position the shield at the top left corner of the wrapper */
    top:0;
    left:0;
    width:100%; /* Take up the entire wrapper */
    height:100%; /* Take up the entire wrapper */
    background: #fff;
    opacity: .8; /* .8 = 80% opacity for all non-ie browsers*/
    -ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=80)"; /* This and the next style are for IE */
    filter: alpha(opacity=80);
}
#gallery_loader img {
    position:relative;
    display:block; /* Need this so we can center the image */
    margin: 150px auto 0 auto; /* Set this to whatever looks good */
    padding: 30px; /* Adjust to your needs */
    background: #fff;
    border: 1px solid #333;
    -moz-border-radius:5px; /* Round corners in mozilla browsers */
    -webkit-border-radius: 5px; /* Round corners for webkit browsers */
}

Put this inside an included javascript file. This will wait until the page is loaded entirely (images and all) and then fade the loader out. Requires jquery.

$(window).bind("load", function() {
	$('#gallery_loader').fadeOut();
});

#gallery_loader is positioned absolutely and placed on top of everything else (z-index:999). It’s set to take up the entire width/height of its parent. Next comes the shield that will actually do the “blocking” of everything in the gallery. The shield is opacited and set to take up the entire width/height of the wrapper. Finally the animated loading image is loaded and centered.

As you can tell from the HTML, the actual shield is not the container of the loading animation gif. This is because the children of transparent elements can’t be more opaque than their parents. In other words if we put the loading image inside the transparent “shield” (which has an opacity of 80%) it would have a max opacity of 80%. To fix this we put the “shield” underneath the loading image and opacitate it. Here’s a good page on opacity.

Note: If you’re having issues where the loading gif isn’t loading immediately add this right after the opening of your body element

<body>
<img src="animated_loader.gif" style="display:none">
...

This will cause the loading gif to load first.

Here is where i obtained my loading gif