(WordPress) my_post_gallery()

<?php
// See gallery_shortcode() for reference.
add_filter( 'post_gallery', 'my_post_gallery', 10, 3 );
function my_post_gallery( $output, $attr, $instance ) {
    $post = get_post();

    // Change #1: I commented out this part.
    /*static $instance = 0;
    $instance++;*/

    if ( ! empty( $attr['ids'] ) ) {
        // 'ids' is explicitly ordered, unless you specify otherwise.
        if ( empty( $attr['orderby'] ) ) {
            $attr['orderby'] = 'post__in';
        }
        $attr['include'] = $attr['ids'];
    }

    // Change #2: I commented out this part.
    /*$output = apply_filters( 'post_gallery', '', $attr, $instance );
    if ( $output != '' ) {
        return $output;
    }*/

    $html5 = current_theme_supports( 'html5', 'gallery' );
    $atts = shortcode_atts( array(
        'order'      => 'ASC',
        'orderby'    => 'menu_order ID',
        'id'         => $post ? $post->ID : 0,
        'itemtag'    => $html5 ? 'figure'     : 'dl',
        'icontag'    => $html5 ? 'div'        : 'dt',
        'captiontag' => $html5 ? 'figcaption' : 'dd',
        'columns'    => 3,
        'size'       => 'thumbnail',
        'include'    => '',
        'exclude'    => '',
        'link'       => ''
    ), $attr, 'gallery' );

    $id = intval( $atts['id'] );

    if ( ! empty( $atts['include'] ) ) {
        $_attachments = get_posts( array( 'include' => $atts['include'], 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $atts['order'], 'orderby' => $atts['orderby'] ) );

        $attachments = array();
        foreach ( $_attachments as $key => $val ) {
            $attachments[$val->ID] = $_attachments[$key];
        }
    } elseif ( ! empty( $atts['exclude'] ) ) {
        $attachments = get_children( array( 'post_parent' => $id, 'exclude' => $atts['exclude'], 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $atts['order'], 'orderby' => $atts['orderby'] ) );
    } else {
        $attachments = get_children( array( 'post_parent' => $id, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $atts['order'], 'orderby' => $atts['orderby'] ) );
    }

    if ( empty( $attachments ) ) {
        return '';
    }

    if ( is_feed() ) {
        $output = "\n";
        foreach ( $attachments as $att_id => $attachment ) {
            $output .= wp_get_attachment_link( $att_id, $atts['size'], true ) . "\n";
        }
        return $output;
    }

    $itemtag = tag_escape( $atts['itemtag'] );
    $captiontag = tag_escape( $atts['captiontag'] );
    $icontag = tag_escape( $atts['icontag'] );
    $valid_tags = wp_kses_allowed_html( 'post' );
    if ( ! isset( $valid_tags[ $itemtag ] ) ) {
        $itemtag = 'dl';
    }
    if ( ! isset( $valid_tags[ $captiontag ] ) ) {
        $captiontag = 'dd';
    }
    if ( ! isset( $valid_tags[ $icontag ] ) ) {
        $icontag = 'dt';
    }

    $columns = intval( $atts['columns'] );
    $itemwidth = $columns > 0 ? floor(100/$columns) : 100;
    $float = is_rtl() ? 'right' : 'left';

    $selector = "gallery-{$instance}";

    $gallery_style = '';

    /**
     * Filters whether to print default gallery styles.
     *
     * @since 3.1.0
     *
     * @param bool $print Whether to print default gallery styles.
     *                    Defaults to false if the theme supports HTML5 galleries.
     *                    Otherwise, defaults to true.
     */
    if ( apply_filters( 'use_default_gallery_style', ! $html5 ) ) {
        $gallery_style = "
        <style type='text/css'>
            #{$selector} {
                margin: auto;
            }
            #{$selector} .gallery-item {
                float: {$float};
                margin-top: 10px;
                text-align: center;
                width: {$itemwidth}%;
            }
            #{$selector} img {
                border: 2px solid #cfcfcf;
            }
            #{$selector} .gallery-caption {
                margin-left: 0;
            }
            /* see gallery_shortcode() in wp-includes/media.php */
        </style>\n\t\t";
    }

    $size_class = sanitize_html_class( $atts['size'] );
    $gallery_div = "<div id='$selector' class='gallery galleryid-{$id} gallery-columns-{$columns} gallery-size-{$size_class}'>";

    /**
     * Filters the default gallery shortcode CSS styles.
     *
     * @since 2.5.0
     *
     * @param string $gallery_style Default CSS styles and opening HTML div container
     *                              for the gallery shortcode output.
     */
    $output = apply_filters( 'gallery_style', $gallery_style . $gallery_div );

    $i = 0;
    foreach ( $attachments as $id => $attachment ) {

        $attr = ( trim( $attachment->post_excerpt ) ) ? array( 'aria-describedby' => "$selector-$id" ) : '';
        if ( ! empty( $atts['link'] ) && 'file' === $atts['link'] ) {
            $image_output = wp_get_attachment_link( $id, $atts['size'], false, false, false, $attr );
        } elseif ( ! empty( $atts['link'] ) && 'none' === $atts['link'] ) {
            $image_output = wp_get_attachment_image( $id, $atts['size'], false, $attr );
        } else {
            $image_output = wp_get_attachment_link( $id, $atts['size'], true, false, false, $attr );
        }
        $image_meta  = wp_get_attachment_metadata( $id );

        $orientation = '';
        if ( isset( $image_meta['height'], $image_meta['width'] ) ) {
            $orientation = ( $image_meta['height'] > $image_meta['width'] ) ? 'portrait' : 'landscape';
        }
        $output .= "<{$itemtag} class='gallery-item'>";
        $output .= "
            <{$icontag} class='gallery-icon {$orientation}'>
                $image_output
            </{$icontag}>";
        if ( $captiontag && trim($attachment->post_excerpt) ) {
            $output .= "
                <{$captiontag} class='wp-caption-text gallery-caption' id='$selector-$id'>
                " . wptexturize($attachment->post_excerpt) . "
                </{$captiontag}>";
        }
        $output .= "</{$itemtag}>";
        // Change #3: I commented out this code.
        /*if ( ! $html5 && $columns > 0 && ++$i % $columns == 0 ) {
            $output .= '<br style="clear: both" />';
        }*/
    }

    // Change #4: I commented out this code.
    /*if ( ! $html5 && $columns > 0 && $i % $columns !== 0 ) {
        $output .= "
            <br style='clear: both' />";
    }*/

    // Change #5: Here's the only one `br` tag we need.
    $output .= "
            <br style='clear: both' />
        </div>\n";

    return $output;
}