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automatically css sprite.

Best Practices

I have written posts “css sprite best practices” to introduce the idea that the css_sprite gem follows.

english version

chinese version

otaviofcs wrote a brazilian version to introduce the css_sprite gem, check it here and he also build a demo

What css_sprite does?

css sprite generates css_sprite image and css files automatically for you follow the conventions as follows.

images under css_sprite directoryclass name in css_sprite css
icons/twitter_icon.png.icons .twitter_icon
widget/icons/twitter_icon.png.widget .icons .twitter_icon
logos_hover/gmail_logo.png.logos:hover .gmail_logo
logos-hover/gmail-logo.png.logos:hover .gmail-logo
logos_active/ .gmail_logo
logos-active/ .gmail-logo

css_sprite directory is the directory whose name is "css_sprite" or "css_sprite" suffixed under app/assets/images directory.

css_sprite image is the image file automatically generated under app/assets/images directory.

css_sprite css is the css file automatically generated under app/assets/stylesheets directory.


css_sprite depends on the mini_magick gem

css_sprite also depends on the optipng tool as default image optimization, but you can use any other image optimization tool, check the Configuration section.

If you use the default optipng tool, please make sure it is successfully installed on your system.

install css_sprite as a gem:

gem install css_sprite


1. create a directory whose name is css_sprite or ends with css_sprite (e.g. widget_css_sprite) under app/assets/images directory

2. if you css_sprite in rails2 projects, you should add css_sprite task in Rakefile

require 'css_sprite'

If you use rails3, you can skip this step too

3. define config/css_sprite.yml, it is not necessary by default.

4. start css_sprite server

rake css_sprite:start

5. put any images which you need to do the css sprite under the css_sprite directory, then you will see the automatically generated css sprite image and css files.

6. include the stylesheet in your view page

<%= stylesheet_link_tag 'css_sprite' %>

You can stop the css_sprite server by rake css_sprite:stop

You can restart the css_sprite server by rake css_sprite:start

Or you can just do the css sprite manually by rake css_sprite:build


There is no need to do any configurations by default for Rails 3.1 or higher projects. If you want some customizations as follows, you need to define config/css_sprite.yml file.

Example for rails 2.x or 3.0

engine: css
image_path: public/images
stylesheet_path: public/stylesheets
css_images_path: images
source_images_path: app/sprites

Destination Image Format

css_sprite saves the css sprite image as a png file by default. You can change it to gif or any other format like

format: GIF

Use asset-url

css_sprite generate background: url('css_sprite.png') no-repeat by default, if you prefer background: asset-url('css_sprite.png') no-repeat, you can change it as follows

use_asset_url: true


css_sprite generates css.scss file by default. You can change it to pure css or sass as you like.

engine: css

engine: css.sass

Image Optimization

css_sprite allows to do optimization to generated css_sprite.png, you can use default optipng with optimization level 2.

optimization: true

Or you can change it to any image optimization command.

optimization: optipng -o 7

Customization styles

For css or scss

  button: |
    text-indent: -9999px;
    display: block;
    cursor: pointer;
    font-size: 0;
    line-height: 15px;
    border: 0;
    outline: 0;
  icon: |
    text-indent: -9999px;
    cursor: pointer;

For sass

engine: sass
  button: |
    text-indent: -9999px
    display: block
    cursor: pointer
    font-size: 0
    line-height: 15px
    border: 0
    outline: 0
  icon: |
    text-indent: -9999px
    cursor: pointer

engine defines css.scss (default), pure css or sass file to generate.

suffix defines the customization styles for specified images.

The customization above means if your image filename is button suffixed (e.g. post_button.png), the corresponding class .post_button has the additional style with (outline: 0; border: 0; and so on), if your image filename is icon suffixed (e.g. twitter_icon.png), the correspondiing class .twitter_icon has the additional style with (text-indent: -9999px; cursor: pointer)

Customization directories

css_sprite follows the conventions that images are under app/assets/images directory and css files are under app/assets/stylesheets, but you can change them.

image_path: public/images
stylesheet_path: public/stylesheets
source_images_path: app/sprites

By default, source_images_path and image_path are app/assets/images and stylesheet_path is app/assets/stylesheets.


I built an example

images are under app/assets/images/css_sprite/

generated css sprite image is at app/assets/images/css_sprite.png

genereated css file is at app/assets/stylesheets/css_sprite.css

$ cd example
$ rake css_sprite:build
$ open index.html

Copyright (c) 2009 - 2013 [Richard Huang], released under the MIT license


automatically css sprite



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