Erskine's sprite mixin

sprite-mixin.scss

@mixin sprite-bg($crop, $x:0, $y:$x, $hover:true) { 
    $i:0; 
    @each $part in $sprite { 
        @if ($part == $crop) { 
            $i:index($sprite, $part);
        } 
    }
    @if $i == 0 { 
        @warn "sprite-bg can't find '#{$crop}' in $sprite"; 
    } 
    background-image:url("/static/images/icons/sprite.png");
    background-position-x: ($x * 1px); 
    background-position-y: ((($i - 1) * ($spritegrid * -1px)) + $y); 
    background-repeat:no-repeat; 
    @if $hover { 
        &:hover, 
        &:focus { 
            background-position-x: (($spritegrid * -1px) + ($x * 1px));
        } 
    } 
    .svg & { background-image:url("/static/images/icons/sprite.svg"); 
    } 
}