CSS sprites technique reduces the number of HTTP requests made for image resources. It combines multiple file images in a single file.
These are two-dimensional images that are made up by combining small images into one larger image at specified X and Y coordinates.
You can use the CSS background-position property for defining the exact position of the image to be displayed for displaying a single image from the combined image.
A web page with several images, particularly several small ones, like buttons, icons, etc., can take longer to load and generate multiple server requests.
The use of image sprites rather than separate images will significantly decrease the number of HTTP requests a browser will make to the server. As a result, image sprites can effectively improve the web pages loading time and overall website performance.
Note: Response time makes a web page more responsive for the user, and reducing the HTTP requests has a significant impact on reducing response time.
See the following examples, and you will notice one visible difference; when the mouse pointer is placed over the browser icons in the non-sprite version for the very first time, the hover image appears after some time. The reason is that the hover picture is loaded from the server on mouse hover because the hover and normal images are two different images. In contrast, in the image sprite version, the hover image is displayed immediately on the hover of a mouse, resulting in a smooth hover effect because all images are combined in a single image.
With the use of the CSS sprite technique illustrated in the: [EXAMPLE - B], you will be able to reduce the HTTP requests number by nine and the images' total file size by 38.2 KB in comparison to the [EXAMPLE - A];. It's a significant improvement in such an example. So think what you can do on the whole website.
In the section below, the entire process of creating this example has been explained below.
To make this sprite image, ten separate images were combined in a single image (mySprite.png). Of course, you can use any image editing tool you like to create your own sprite.
Tip: For convenience, all icons of the same size were used and were placed close to each other to calculate the offset easily.
Finally, using CSS, you can display just the part of an image sprite you need.
Firstly, you will create the class .sprite that will load your sprite image. It is for avoiding repetition since all items share the same background-image.
Example :
.sprite {
background: url("images/mySprite.png") no-repeat;
}Now, you must define a class for each item you want to display. For example, for displaying the Internet Explorer icon form the image sprite, the CSS code would be.
Example :
.ie {
width: 50px; /* Icon width */
height: 50px; /* Icon height */
display: inline-block; /* Display icon as inline block */
background-position: 0 -200px; /* Icon background position in sprite */
}
The next question is how to get those pixel values for background-position? Let's see. The first value is the horizontal position of the background, and the second value is the vertical position of the background. Since the upper-left corner of the icon of Internet Explorer touches the left edge, therefore, its horizontal distance from the starting point, that is, image sprite's top-left corner is 0. Since, it is placed on the fifth position therefore its vertical distance from the image sprite starting point is 4 X 50px = 200px, since each icon's height is 50px.
For showing the Internet Explorer icon, we moved its upper-left corner to the starting point, i.e., image sprite's top-left corner (mySprite.png). Moreover, since the icon is placed at the vertical distance of 200px, we need to shift the complete background-image (mySprite.png) vertically up by 200px, for which we need to apply the value as a negative number, i.e., -200px. The negative value makes an icon go vertically up, and on the contrary, a positive value would move an icon down. However, the icon does not need a horizontal offset because there are no pixels before the Internet Explorer icon's upper-left corner.
Tip: Simply play with the background-position property value in the upcoming examples, and you will learn how the offsets work easily.
The previous section teaches you a method of displaying an individual icon from an image sprite. It is one of the easiest methods of using image sprites; now, let's go ahead and build a navigation menu with a rollover effect, as illustrated in [EXAMPLE - B].
Here we use the same sprite image (mySprite.png) for creating our navigation menu.
Let's start by creating our navigation menu with an HTML unordered list.
Example:
<ul class="menu">
<li class="firefox"><a href="#">Firefox</a></li>
<li class="chrome"><a href="#">Chrome</a></li>
<li class="ie"><a href="#">Explorer</a></li>
<li class="opera"><a href="#">Opera</a></li>
<li class="safari"><a href="#">Safari</a></li>
</ul>The next section describes a method of converting the simple unordered list given in the example mentioned above to a sprite image on the basis of navigation utilizing CSS.
HTML unordered lists are displayed with bullets by default. Therefore, we need to remove the default bullets by setting the list-style-type attribute to none.
Example :
ul.menu {
list-style-type: none;
}
ul.menu li {
padding: 5px;
font-size: 16px;
font-family: "Trebuchet MS", Arial, sans-serif;
}The next step is to set all the common CSS properties that all links will share. Like, color, background-image, padding, display, etc.
Example :
ul.menu li a {
height: 50px;
line-height: 50px;
display: inline-block;
padding-left: 60px; /* To sift text off the background-image */
color: #3E789F;
background: url("images/mySprite.png") no-repeat; /* As all link share the same background-image */
}In this step, it is must to define a class for each menu item since each item in the image sprite has a distinct background-position. For instance, the Firefox icon's placement is at the starting point, i.e., image sprite's top-left corner, so there is no requirement to shift the background-image. Therefore, the horizontal and vertical position of the background, in this case, would be 0. Likewise, the background-position can be defined for other icons within the image sprite.
Example :
ul.menu li.firefox a {
background-position: 0 0;
}
ul.menu li.chrome a {
background-position: 0 -100px;
}
ul.menu li.ie a {
background-position: 0 -200px;
}
ul.menu li.safari a {
background-position: 0 -300px;
}
ul.menu li.opera a {
background-position: 0 -400px;
}Adding hover states of links has the same principle as adding the above links. You just need to move their upper-left corner to the image sprite's starting point (i.e., top-left corner) as done above. The background-position can be calculated using the below-mentioned formula:
Vertical position of hover state = Vertical position of normal state - 50px
Since rollover images are right below the default, each icon's state and height are equal to 50px. The icon's hover state also doesn't need a horizontal offset, as there are no pixels before the upper-left corner.
Example :
ul.menu li.firefox a:hover {
background-position: 0 -50px;
}
ul.menu li.chrome a:hover {
background-position: 0 -150px;
}
ul.menu li.ie a:hover {
background-position: 0 -250px;
}
ul.menu li.safari a:hover {
background-position: 0 -350px;
}
ul.menu li.opera a:hover {
background-position: 0 -450px;
}The final HTML and CSS code after combining the entire process:
Example :
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Example of Sprite Navigation Menu</title>
<style>
ul.menu {
list-style-type: none;
}
ul.menu li {
padding: 5px;
font-size: 16px;
font-family: "Trebuchet MS", Arial, sans-serif;
}
ul.menu li a {
height: 50px;
line-height: 50px;
display: inline-block;
padding-left: 60px; /* To sift text off the background-image */
color: #3E789F;
background: url("images/mySprite.png") no-repeat; /* As all link share the same background-image */
}
ul.menu li.firefox a {
background-position: 0 0;
}
ul.menu li.chrome a {
background-position: 0 -100px;
}
ul.menu li.ie a {
background-position: 0 -200px;
}
ul.menu li.safari a {
background-position: 0 -300px;
}
ul.menu li.opera a {
background-position: 0 -400px;
}
ul.menu li.firefox a:hover {
background-position: 0 -50px;
}
ul.menu li.chrome a:hover {
background-position: 0 -150px;
}
ul.menu li.ie a:hover {
background-position: 0 -250px;
}
ul.menu li.safari a:hover {
background-position: 0 -350px;
}
ul.menu li.opera a:hover {
background-position: 0 -450px;
}
</style>
</head>
<body>
<ul class="menu">
<li class="firefox"><a href="#">Firefox</a></li>
<li class="chrome"><a href="#">Chrome</a></li>
<li class="ie"><a href="#">Explorer</a></li>
<li class="opera"><a href="#">Opera</a></li>
<li class="safari"><a href="#">Safari</a></li>
</ul>
</body>
</html>