Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.5)
// Compass (v1.0.0.alpha.18)
// ----

@mixin image2x-retina($file, $type, $width, $height, $mod: '@2x') {
  $fileName: $file + '.' + $type;
  $retina: $file + $mod + '.' + $type;
  
  background-image: url($fileName);
  
  @media (-webkit-min-device-pixel-ratio: 1.5), (-moz-min-device-pixel-ratio: 1.5) {
    & {
      background-image: url($retina);
      background-size: $width $height;
    }
  }
}

// Example
#foo {
  @include image2x-retina('foobar', 'png', 10px, 20px);
  background: repeat;
}

SassMeister-output.css

#foo {
  background-image: url("foobar.png");
  background: repeat;
}
@media (-webkit-min-device-pixel-ratio: 1.5), (-moz-min-device-pixel-ratio: 1.5) {
  #foo {
    background-image: url("foobar@2x.png");
    background-size: 10px 20px;
  }
}