custom-wordpress-gallery-shortcode.php

<?php
/**
 *  Disable Default Gallery
 */
remove_shortcode('gallery', 'gallery_shortcode');
/**
 *  Custom Gallery
 */
add_shortcode( 'gallery', 'custom_gallery_shortcode' );
function custom_gallery_shortcode( $attributes ) {
  $data = shortcode_atts( array(
    'ids' => ''
  ), $attributes );
  $image_ids = explode(',', $data['ids']);
  $view = '<div class="wrap">';
  $counter = 0;
  foreach ($image_ids as $id) {
    if ( $counter % 3 == 0 ) {
      $view .= $counter > 0 ? '</div>' : '';
      $view .= '<div class="row">';
    }
    $view .= '<div class="col">';
      $view .= '<img src="'.wp_get_attachment_thumb_url($id).'">';
    $view .= '</div>';
    $counter++;
  }
  $view .= '</div>';
  return $view;
}