Friday 29 January 2010

jQuery image roll-overs

On the site I am currently working on I needed to implement hover/roll-over states for a number of image tags. Other elements in the site use the CSS based x:hover{background:y} approach, but that was not an appropriate solution for these instances - background images were not going to used, so I came up with a nice jQuery based solution that keeps my page-source pretty uncluttered too.

I added a class value of "hover" to the image tags I wanted to exhibit this behaviour. The replacement images all had the suffix _hover added (e.g. theimage_hover.png )

<img src="/images/theimage.png" class="hover">

Then in my main javascript file I added this little snippet:

function imghover_on(img){if(img.src.indexOf('_hover.')==-1){img.src=img.src.substr(0,img.src.length-4)+'_hover'+img.src.substr(img.src.length-4)}}

function imghover_off(img){img.src = img.src.replace('_hover.','.');}

jQuery("img.hover").mouseenter(function(e){ imghover_on(this);});
jQuery("img.hover").mouseleave(function(e){ imghover_off(this);});

This code declares two functions which add or remove the "_hover" suffix to the image tag's source, while not needing to know if the image is .png .gif or .jpg.

The jQuery statement waits for the page to load and then finds all img tags in the document with the hover class set and binds the function calls to the mouseenter and mouseleave. This saves me from having to add these events to every single image tag manually like this:

<img src="/images/theimage.png" onmouseover="imghover_on(this);" onmouseout="imghover_off(this)">


  • I used mouseenter/mouseleave as they fire a lot less than mouseover/mouseout (see: )
  • It's not infallable, a .jpeg file extension would fail, but it's working nicely for first cut.

Wednesday 20 January 2010

WordPress Theme URL Tip

Lately I've been putting a lot of hours into developing a couple of sites using the WordPress and WPMU platforms. These platforms are a solid starting point for pulling a content/post based site together relatively quickly - the wealth of useful plugins also helps reduce the chance of you having to re-invent the wheel.

Having said that there is still a lot to do to create a professional website that has it's own look and feel - much of this can be achieved by creating a custom theme.

If you are creating a custom theme you will probably need to link to multiple elements within that theme's directory structure. The most common approach to do this is somthing like this:

<img src="<?php bloginfo('stylesheet_directory'); ?>/images/myimage.png">

echo '<img src="'.get_bloginfo('stylesheet_directory').'/images/myimage.png">';

I've certainly been using a lot of the latter style, until today.

I decided to clean up my code a bit and put the following line at the top of my theme's functions.php file:

if(!defined('WP_THEME_URL')) {
define( 'WP_THEME_URL', get_bloginfo('stylesheet_directory'));

Then I replaced all the get_bloginfo('stylesheet_directory') instances with the constant WP_THEME_URL. Now my code is a lot more readable and there is less typing.

<img src="<?php echo WP_THEME_URL; ?>/images/myimage.png">

echo '<img src="'.WP_THEME_URL.'/images/myimage.png">';

Using a constant like this should provide a slight performance increase here too - I haven't done any performance tests, but the current get_bloginfo() process is a fairly convoluted chain of function calls.

Note: Just in case the WP platform does start using this constant in the future, the constant's value is not set if it is already defined.

UPDATE: After this post was made I discovered WordPress defines a TEMPLATEPATH constant, but no constant currently exists for the TEMPLATEURL.

Saturday 9 January 2010

Animated "Loading" Image Generator

Yesterday somebody sent me an email introducing me to and it's such a handy tool I thought I should share it here.

Generate a customised animated gif by choosing the style you want, the background and foreground colors and whether the background should be transparent.

Here are some quick examples...