Using Compass to generate retina sprite maps at once

_compass-retina-sprites.scss

@mixin all-retina-sprites($map, $dimensions: false){
  $base-class: sprite-map-name($map);

  .#{$base-class}-retina-sprite{
    background: sprite-url($map) no-repeat;
    @include background-size(ceil(image-width(sprite-path($map)) / 2) auto);
  }

  @each $sprite in sprite-names($map){
    .#{$base-class}-#{$sprite}{
      @extend .#{$base-class}-retina-sprite;
      @if $dimensions{
        width: ceil(image-width(sprite-file($map, $sprite)) / 2);
        height: ceil(image-height(sprite-file($map, $sprite)) / 2);
      }
      $pos: sprite-position($map, $sprite);
      background-position: ceil(nth($pos, 1) / 2) ceil(nth($pos, 2) / 2);
    }
  }
}

_sprites.scss

// Sprite set: General
// ----------------------------------------
//$general-layout: smart;

$general-retina-spacing: 1px;
@import "general-retina/*.png";
//@include all-general-retina-sprites;

@include all-retina-sprites($general-retina-sprites, $dimensions: true);