@mixin retina-image($filename, $background-size, $extension: png, $retina-filename: null, $asset-pipeline: false) { background-image: url($filename + "." + $extension); @include hidpi { @if $asset-pipeline { @if $retina-filename { background-image: image_url($retina-filename + "." + $extension); } @else { background-image: image_url($filename + "@2x" + "." + $extension); } } @else { @if $retina-filename { background-image: url($retina-filename + "." + $extension); } @else { background-image: url($filename + "@2x" + "." + $extension); } } background-size: $background-size; } }