Adding post_gallery filter to incorporate BS4 markup

functions.php

@@ -67,6 +67,11 @@ require get_template_directory() . '/inc/bootstrap-wp-navwalker.php';
 */
 require get_template_directory() . '/inc/bootstrap-wp-pagination.php';
 
+/**
+* Load custom WordPress gallery.
+*/
+require get_template_directory() . '/inc/bootstrap-wp-gallery.php';
+
 
 /**
 * Load WooCommerce functions.

inc/bootstrap-wp-gallery.php

@@ -0,0 +1,132 @@
+
+
+<?php
+//Based on Jeff Hays code and his article here: http://robido.com/wordpress/wordpress-gallery-filter-to-modify-the-html-output-of-the-default-gallery-shortcode-and-style/ 
+// Custom filter function to modify default gallery shortcode output
+function bootstrap_wp_gallery( $output, $attr ) {
+
+
+	// Initialize
+	global $post, $wp_locale;
+
+	// Gallery instance counter
+	static $instance = 0;
+	$instance++;
+
+	// Validate the author's orderby attribute
+	if ( isset( $attr['orderby'] ) ) {
+		$attr['orderby'] = sanitize_sql_orderby( $attr['orderby'] );
+		if ( ! $attr['orderby'] ) unset( $attr['orderby'] );
+	}
+
+	// Get attributes from shortcode
+	extract( shortcode_atts( array(
+		'order'      => 'ASC',
+		'orderby'    => 'menu_order ID',
+		'id'         => $post->ID,
+		'itemtag'    => 'div',
+		'icontag'    => 'div',
+		'captiontag' => 'div',
+		'columns'    => 3,
+		'size'       => 'thumbnail',
+		'include'    => '',
+		'exclude'    => ''
+	), $attr ) );
+
+	// Initialize
+	$id = intval( $id );
+	$attachments = array();
+	if ( $order == 'RAND' ) $orderby = 'none';
+
+
+	if ( ! empty( $include ) ) {
+
+		// Include attribute is present
+		$include = preg_replace( '/[^0-9,]+/', '', $include );
+		$_attachments = get_posts( array( 'include' => $include, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby ) );
+
+		// Setup attachments array
+		foreach ( $_attachments as $key => $val ) {
+			$attachments[ $val->ID ] = $_attachments[ $key ];
+		}
+
+	} else if ( ! empty( $exclude ) ) {
+
+		// Exclude attribute is present 
+		$exclude = preg_replace( '/[^0-9,]+/', '', $exclude );
+
+		// Setup attachments array
+		$attachments = get_children( array( 'post_parent' => $id, 'exclude' => $exclude, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby ) );
+	} else {
+		// Setup attachments array
+		$attachments = get_children( array( 'post_parent' => $id, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby ) );
+	}
+
+	if ( empty( $attachments ) ) return '';
+
+	// Filter gallery differently for feeds
+	if ( is_feed() ) {
+		$output = "\n";
+		foreach ( $attachments as $att_id => $attachment ) $output .= wp_get_attachment_link( $att_id, $size, true ) . "\n";
+		return $output;
+	}
+
+	// Filter tags and attributes
+	$itemtag = tag_escape( $itemtag );
+	$captiontag = tag_escape( $captiontag );
+	$columns = intval( $columns );
+	$itemwidth = $columns > 0 ? floor( 12 / $columns ) : 100;
+	$float = is_rtl() ? 'right' : 'left';
+	$selector = "gallery-{$instance}";
+
+ // Filter gallery CSS
+	$output = apply_filters( 'gallery_style', "
+
+		<div id='$selector' class='gallery galleryid-{$id} row'>"
+	);
+
+	// Iterate through the attachments in this gallery instance
+	$i = 0;
+	foreach ( $attachments as $id => $attachment ) {
+
+		// Attachment link
+		$link = isset( $attr['link'] ) && 'file' == $attr['link'] ? wp_get_attachment_link( $id, $size, false, false ) : wp_get_attachment_link( $id, $size, true, false ); 
+
+		// Start itemtag
+		$output .= "<{$itemtag} class='gallery-item col-md-{$itemwidth}'>";
+
+		// icontag
+		$output .= "
+		<{$icontag} class='gallery-icon'>
+			$link
+		</{$icontag}>";
+
+		if ( $captiontag && trim( $attachment->post_excerpt ) ) {
+
+			// captiontag
+			$output .= "
+			<{$captiontag} class='gallery-caption'>
+				" . wptexturize($attachment->post_excerpt) . "
+			</{$captiontag}>";
+
+		}
+
+		// End itemtag
+		$output .= "</{$itemtag}>";
+
+		// Line breaks by columns set
+		if($columns > 0 && ++$i % $columns == 0) $output .= '<br style="clear: both">';
+
+	}
+
+	// End gallery output
+	$output .= "
+		<br style='clear: both;'>
+	</div>\n";
+
+	return $output;
+
+}
+
+// Apply filter to default gallery shortcode
+add_filter( 'post_gallery', 'bootstrap_wp_gallery', 10, 2 );

inc/enqueue.php

@@ -31,7 +31,6 @@ function understrap_slider(){
     	"items"=>get_theme_mod( 'understrap_theme_slider_count_setting', 1 )
     	);
 
-
     wp_enqueue_script("understrap-slider-script", get_stylesheet_directory_uri() . '/js/slider_settings.js', array(), '0.4.3');
     wp_localize_script( "understrap-slider-script", "understrap_slider_variables", $data );
     }