_example.scss

// Example

.example {
  @include get-sprite($sprites, 'example-image');
  @include at-retina() {
    @include get-sprite($sprites2x, 'example-image');
  }
}

_mixins.scss

// Mixins

// http://compass-style.org/reference/compass/helpers/sprites/
@mixin get-sprite($map, $sprite, $repeat: no-repeat, $height: false, $width: false, $offset-x: 0, $offset-y: 0) {

  //http://compass-style.org/reference/compass/helpers/sprites/#sprite-file
  $sprite-image: sprite-file($map, $sprite);

  // http://compass-style.org/reference/compass/helpers/sprites/#sprite-url
  $sprite-map: sprite-url($map);

  // http://compass-style.org/reference/compass/helpers/sprites/#sprite-position
  $sprite-position: sprite-position($map, $sprite, $offset-x, $offset-y);
  background: $sprite-map $sprite-position $repeat;

  // divide background size and position by 2
  @include at-retina() {
    $sprite-position: (nth($sprite-position, 1) / 2) (nth($sprite-position, 2) / 2);
    background: $sprite-map $sprite-position $repeat;
    background-size: (image-width(sprite-path($map)) / 2) (image-height(sprite-path($map)) / 2);
  }

  // http://compass-style.org/reference/compass/helpers/image-dimensions/
  // Checks to see if the user wants height returned
  @if $height == true {
    // Gets the height of the sprite-image
    $sprite-height: image-height($sprite-image);
    // Returns the height
    height: $sprite-height;
  }

  // http://compass-style.org/reference/compass/helpers/image-dimensions/
  // Checks to see if the user wants height returned
  @if $width == true {
    // Gets the width of the sprite-image
    $sprite-width: image-width($sprite-image);
    // Returns the width
    width: $sprite-width;
  }
}

@mixin at-retina() {
  @media
  only screen and (-webkit-min-device-pixel-ratio: 2),
  only screen and (min-resolution: 192dpi) {
    @content;
  }
}

_sprites.scss

// Sprites

$sprites: sprite-map("sprites/*.png", $spacing: 20px);
$sprites2x: sprite-map("sprites2x/*.png", $spacing: 40px);

only works if every non-retina image also has a retina version set. Needs fix.