Generate data tags for http://jquerypicture.com/ usable in Wordpress

.php

<?php
/**
 * Responsive bg data 
 * 
 * @see http://jquerypicture.com/
 */
function generate_reponsive_bg() {
	global $post, $_wp_additional_image_sizes;
	
	
	// smallest one	from 0 to 768
	$img = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'sm');
	
	echo 'data-media="' . $img[0] . '" ';
	unset( $img );
	
	/** @var array $sizes id of additional sizes **/
	$sizes = array_keys( $_wp_additional_image_sizes );
	$sizes[] = 'full';
	
	// remove sm (it's already printed)
	array_shift( $sizes );
	
	/** @var array $widths **/
	$widths = array_column( $_wp_additional_image_sizes, 'width' );
	
	// combine id with shifted values
	$sizes = array_combine( $sizes, $widths );
	
	// print data tags & FIN
	foreach( $sizes as $id => $size ) {
		$url = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), $id );
		echo 'data-media' . $size . '="' . $url[0] . '" ';
	}
}