retina_support_attachment_meta

add_filter( 'wp_generate_attachment_metadata', 'retina_support_attachment_meta', 10, 2 );
function retina_support_attachment_meta( $metadata, $attachment_id ) {
    foreach ( $metadata as $key => $value ) {
        if ( is_array( $value ) ) {
            foreach ( $value as $image => $attr ) {
                if ( is_array( $attr ) )
                    retina_support_create_images( get_attached_file( $attachment_id ), $attr['width'], $attr['height'], true );
            }
        }
    }
    return $metadata;
}