@function calculate-atlas-width($images)
  $sprite-names: sprite-names($images)
  $width: 0px
  @each $sprite-name in $sprite-names 
    @if $sprite-name != nil and $images != nil
      $tmp-width: image-width(sprite-file($images, $sprite-name))
      @if $tmp-width > $width
        $width: $tmp-width
  @return $width

@mixin build-sprite-atlas( $images, $size: normal )
  background-image: $images
  background-repeat: no-repeat
  @if $size == retina
    @include background-size( calculate-atlas-width($images) /2 auto)

@mixin build-sprite-css( $images, $name, $size: normal )
  $spt_pos: sprite-position($images, $name)
  $xpos: 0
  $ypos: 0
  $width: 0
  $height: 0
  @if $size == retina
    $xpos: round(nth($spt_pos, 1) / 2)
    $ypos: round(nth($spt_pos, 2) / 2)
    $height: image-height(sprite-file($images, $name))/2
    $width: image-width(sprite-file($images, $name))/2
  @else
    $xpos: round(nth($spt_pos, 1))
    $ypos: round(nth($spt_pos, 2))
    $height: image-height(sprite-file($images, $name))
    $width: image-width(sprite-file($images, $name))
  background-position: $xpos $ypos
  width: $width
  height: $height

@mixin sprite-half-position( $images, $name, $size )
  $spt_pos: sprite-position($images, $name)
  $width: 0
  $height: 0
  @if $size == retina
    $height: image-height(sprite-file($images, $name))/2
    $width: image-width(sprite-file($images, $name))/2
  @else
    $height: image-height(sprite-file($images, $name))
    $width: image-width(sprite-file($images, $name))
  left: -($width/2)
  top: -($height/2)

@mixin find-sprite( $images, $name, $size: normal )
  @include build-sprite-atlas( $images, $size )
  @include build-sprite-css( $images, $name, $size )

@mixin build-sprites($name, $images, $size: normal)
  $sprite-names: sprite-names($images)

  @each $sprite-name in $sprite-names
    .#{$name}-#{$sprite-name}
      @include build-sprite-atlas( $images, $size )
      @include build-sprite-css( $images, $sprite-name, $size )