Retina sprite background image mixin.

_retina-sprite-background.scss

/*
This pretty much doesn't work at all right now.
*/
@mixin retina-general-sprite($name, $set-dimensions: true) {
  $sprite-width: image-width('general.png');
  $sprite-height: image-height('general.png');
  
  $sprite-file-url: sprite-file($general-sprite, $name);
  $sprite-file-width: image-width($sprite-file-url) / 2;
  $sprite-file-height: image-height($sprite-file-url) / 2;
  
  @if $set-dimensions {
    display: block;
    width: $sprite-file-width;
    height: $sprite-file-height;
  }
  
  background: no-repeat image-url('general.png');
  background-position: sprite-position($general-sprite, $name);
//  background-size: 100%;
  background-size: $sprite-file-width $sprite-file-height;
}

config.rb

# Add this to the config.rb to remove the random string on the back of the sprite filename.
on_sprite_saved do |filename|
  if File.exists?(filename)
    FileUtils.mv filename, filename.gsub(%r{-s[a-z0-9]{10}\.png$}, '.png')
  end
end

I realize this wasn't as clear as it could be, but by 'standalone images', I mean this could work for sprites that are not generated by Compass as well.