Custom slideshow gallery format

gallery.php

<?php
/**
 * Get the [gallery] shortcode from the post content and display it on index page. It require
 * gallery ids [gallery ids=1,2,3,4] to display it as thumbnail slideshow. If no ids exist it
 * just display it as standard [gallery] markup.
 *
 * If no [gallery] shortcode found in the post content, get the attached images to the post and 
 * display it as slideshow.
 * 
 * @since  2.1
 * @access public
 * @uses   get_post_gallery() to get the gallery in the post content.
 * @uses   wp_get_attachment_image() to get the HTML image.
 * @uses   get_children() to get the attached images if no [gallery] found in the post content.
 * @return string
 */
function satu_get_format_gallery() {
	global $post;

	/* Don't display it on single post. */
	if ( is_singular() )
		return;

	/* Set up a default, empty $html variable. */
	$html = '';

	/* Check the [gallery] shortcode in post content. */
	$gallery = get_post_gallery( $post->ID, false );

	/* Check if the [gallery] exist. */
	if ( $gallery ) {

		/* Check if the gallery ids exist. */
		if ( isset( $gallery['ids'] ) ) {

			/* Get the gallery ids and convert it into array. */
			$ids = explode( ',', $gallery['ids'] );

			/* Display the gallery in a cool slideshow on index page. */
			$html = '<ul class="rslides">';
				foreach( $ids as $id ) {
					$html .= '<li>';
					$html .= wp_get_attachment_image( $id, 'satu-featured' );
					$html .= '</li>';
				}
			$html .= '</ul>';

		} else {

			/* If gallery ids not exist, display the standard gallery markup. */
			$html = get_post_gallery( $post->ID );

		}

	/* If no [gallery] in post content, get attached images to the post. */
	} else {

		/* Set up default arguments. */
		$defaults = array( 
			'order'          => 'ASC',
			'post_type'      => 'attachment',
			'post_parent'    => $post->ID,
			'post_mime_type' => 'image',
			'numberposts'    => -1
		);

		/* Retrieves attachments from the post. */
		$attachments = get_children( apply_filters( 'satu_gallery_format_args', $defaults ) );

		/* Check if attachments exist. */
		if ( $attachments ) {

			/* Display the attachment images in a cool slideshow on index page. */
			$html = '<ul class="rslides">';
				foreach ( $attachments as $attachment ) {
					$html .= '<li>';
					$html .= wp_get_attachment_image( $attachment->ID, 'satu-featured' );
					$html .= '</li>';
				}
			$html .= '</ul>';

		}

	}

	/* Return the gallery images. */
	return $html;

}