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I want to overwrite the default WordPress gallery shortcode with a custom one. This because I need to add a field that will contain an url for each image I want to add inside a gallery. I'm not sure how to proceed, but for now I wrote this prototype of the code I want to use for the shortcode, I'm not sure how to proceed for the custom link field. Also I need to understand how to open the media library modal to multiselect the images and add to the shortcode id param, the various ids of the images and their relative links. Any suggestion or help will be appreciated.


function custom_gallery( $atts ){
  extract(shortcode_atts('id' => '','links' => '')); 
  // here I need to implement code for link and image selection
}
add_shortcode( 'gallery', 'custom_gallery');


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At the top of the Gallery Shortcode Callback is a filter hook: post_gallery

If any non-empty / non-null output is returned from this filter the shortcode will use that output instead of the default generation. You can copy the source of the Gallery Shortcode Callabck and modify it as you see fit.

The below is a filter hook, using the entire code of the gallery callback with the post_gallery filter hook removed to prevent any infinite looping.

/**
 * Custom Gallery Function for custom output
 * 
 * @param string $output   The gallery output. Default empty.
 * @param array  $attr     Attributes of the gallery shortcode.
 * @param int    $instance Unique numeric ID of this gallery shortcode instance.
 *
 * @return String $output
 */
function my_custom_gallery( $output, $attr, $instance ) {

    $post = get_post();
    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'];
    }

    $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}>";
            if ( ! $html5 && $columns > 0 && ++$i % $columns == 0 ) {
                    $output .= '<br style="clear: both" />';
            }
    }
    if ( ! $html5 && $columns > 0 && $i % $columns !== 0 ) {
            $output .= "
                    <br style='clear: both' />";
    }
    $output .= "
            </div>\n";
            return $output;

}
add_filter( 'post_gallery', 'my_custom_gallery', 10, 3 );
  • This will also give me the ability to add an input text to give each image an unique link? – sialfa Nov 3 at 19:15
  • Yes, this is in the loop so you have access to the global $post and inside the function the $_attachments foreach is where you can get the attachment. – Howdy_McGee Nov 3 at 19:17
  • but how I pass the links, I want to add them using comma separated string in atts array, but with many links I don't think this is the better solution? – sialfa Nov 3 at 19:37
  • You should add post meta for the images for these links. These should be per image and is a separate question. While in the function, foreach of attachments, you can call get_post_meta() – Howdy_McGee Nov 3 at 19:39
  • ok, I will do some research, maybe post meta can be enough for my scope. if you provide an example link I will appreciate it. – sialfa Nov 3 at 20:26

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