Thursday, November 28, 2013

CSS 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.

CSS sprites can be used in various settings. Large websites can combine multiple single images in a meaningful manner, creating clearly separated “chunks” of the master images – the purpose being to keep the design maintainable and easy to update. The large empty space between the images is often used to make sure that the text resizing in browser doesn’t cause side effects such the display of multiple images in the background. In fact, sprites usually work well in a pixel-based design, but they are hard to use in elastic (em-based) designs due to the restricted background-position-property. Essentially, the structure that sprites take depends on the trade-off between maintainability and reduced server load; thus, it varies depending on the project you are working on.

HOw to Use =>

The background-position property, together with CSS specificity and CSS floats, is probably one of the most confusing and counter-intuitive of CSS properties.
According to CSS specifications, the background-position takes two (optional) arguments: horizontal position and vertical position. For example:
.introduction {
background-image: url(bg.gif);
background-position: [horizontal position] [vertical position];
}
Using this property, you can define the exact position of the background image for the block-level element (list item li). You can use either % or px units (or mix both) to define the starting position (i.e. the upper-left corner) of the displayed part of the master image. Alternatively, you could use the following keywords: top left, top center, top right, center left, center center, center right, bottom left, bottom center, bottom right.
Hence, in background-position: x% y%, the first value is the horizontal position, and the second value is the vertical position. The top-left corner is 0% 0%. The bottom-right corner is 100% 100%. If you specify only one value, the other value will be 50%.
For instance, if you use,
ul li {
background-image: url(bg.gif);
background-position: 19px 85px;
},
… then the background-image will be positioned 19 pixels from the left and 85 pixels from the top of the list item element.

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