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CSS Image Sprites

Image Sprites

An image sprite is a collection of images put into a single image.

A web page with many images can take a long time to load and generates
multiple server requests.

Using image sprites will reduce the number of server requests and save
bandwidth.

Image Sprites - Simple Example

Instead of using three separate images, we use this single image ("img_navsprites.gif"):

With CSS, we can show just the part of the image we need.

In the following example the CSS specifies which part of the "img_navsprites.gif"
image to show:

Example explained:

• 
  <img id="home" src="img_trans.gif"> - Only defines a small transparent image
  because the src attribute cannot be empty. The displayed image will be the background image we specify in CSS


• 
  width: 46px; height: 44px; - Defines the portion of the image we want to use


• 
  background: url(img_navsprites.gif) 0 0; - Defines the background image and its position (left 0px, top 0px)

This is the easiest way to use image sprites, now we want to expand it by
using links and hover effects.

Image Sprites - Create a Navigation List

We want to use the sprite image ("img_navsprites.gif") to create a navigation list.

We will use an HTML list, because it can be a link and also supports a background image:

Example explained:

• #navlist {position:relative;} - position is set to relative to allow
  absolute positioning inside it


• #navlist li {margin:0;padding:0;list-style:none;position:absolute;top:0;}
  - margin and padding are set to 0, list-style is removed, and all list items
  are absolute positioned


• #navlist li, #navlist a {height:44px;display:block;} - the height of all
  the images are 44px

Now start to position and style for each specific part:

• #home {left:0px;width:46px;} - Positioned all the way to the left, and
  the width of the image is 46px


• #home {background:url(img_navsprites.gif) 0 0;} -
  Defines the background
  image and its position (left 0px, top 0px)


• #prev {left:63px;width:43px;} - Positioned 63px to the
  right (#home width 46px + some extra space between items), and
  the width is 43px.


• #prev {background:url('img_navsprites.gif') -47px 0;} - Defines the background
  image 47px to the right (#home width 46px + 1px line
  divider)


• #next {left:129px;width:43px;}- Positioned 129px to
  the right (start of #prev is 63px + #prev width 43px +
  extra space), and the width is 43px.


• #next {background:url('img_navsprites.gif') -91px 0;} -
  Defines the background
  image 91px to the right (#home width 46px + 1px
  line divider + #prev width 43px + 1px line divider )

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Image Sprites - Hover Effect

Now we want to add a hover effect to our navigation list.

Our new image ("img_navsprites_hover.gif") contains three navigation images
and three images to use for hover effects:

Because this is one single image, and not six separate files, there will be no
loading delay when a user hovers over the image.

We only add three lines of code to add the hover effect:

Example explained:

• #home a:hover {background: transparent url('img_navsprites_hover.gif') 0 -45px;} - For all three hover images we specify the same background position, only 45px further down