Related Posts using Categories

<?php
/**
 * @link https://kriesi.at/support/topic/related-posts-not-showing/
 */
if ( ! defined( 'ABSPATH' ) ) {  exit;  }    // Exit if accessed directly

/**
 *  These functions shows a number of posts related to the currently displayed post.
 *  Relations are defined by categories: if post categories match, the post will be displayed as related
 */
global $avia_config;


$rp = avia_get_option('single_post_related_entries');




if(!isset($avia_config['related_posts_config']))
{
    $avia_config['related_posts_config'] = array(

    'columns' => 8,
    'post_class' =>  "av_one_eighth no_margin ",
    'image_size' => 'square',
    'tooltip'    => true,
    'title_short'=> false

    );

    if($rp == "av-related-style-full")
    {
        $avia_config['related_posts_config'] = array(

        'columns' => 6,
        'post_class' =>  "av_one_half no_margin ",
        'image_size' => 'square',
        'tooltip'    => false,
        'title_short'=> true
        );
    }
}

if($rp == "disabled") return;







extract($avia_config['related_posts_config']);


$is_portfolio       = false; //avia_is_portfolio_single();
$related_posts      = false;
$this_id            = $post->ID;
$slidecount         = 0;
$postcount          = ($columns * 1);
$format             = "";
$fake_image         = "";
$categories         = wp_get_post_categories($this_id);

if (!empty($categories) && is_array($categories))
{
     $category_ids = array();
     foreach ($categories as $category ) {
        $category_ids[] = (int)$category;
    }

     if(!empty($category_ids))
     {


        $my_query = get_posts(
                            array(
                                'category__in' => $category_ids,
                                'post_type' => get_post_type($this_id),
                                'showposts'=>$postcount, 'ignore_sticky_posts'=>1,
                                'orderby'=>'rand',
                                'post__not_in' => array($this_id))
                            );

        if (!empty($my_query))
        {
            $extra = 'alpha';
            $count = 1;
            $output = "";

            //create seperator

            $output .= "<div class ='related_posts clearfix {$rp}'>";


            $output .= "<h4 class='related_title'>".__('You might also like', 'avia_framework')."</h4>";
            $output .= "<div class='related_entries_container '>";

            foreach ($my_query as $related_post)
            {
                $related_posts = true;
                $slidecount ++;
                $format = "";
                if($is_portfolio) $format = "portfolio";
                if(!$format) $format = get_post_format($related_post->ID);
                if(!$format) $format = 'standard';
                if( ! empty( $title_short ) )
                {
                    $related_post->post_title = wp_trim_words( avia_wp_get_the_title( $related_post->ID ), 17 );
                }

                $post_thumbnail_id = get_post_thumbnail_id($related_post->ID);
                $post_thumb = get_the_post_thumbnail($related_post->ID, $image_size, array('title' => esc_attr(get_the_title($post_thumbnail_id))));
                $image      = $post_thumb ? $post_thumb : "<span class='related_posts_default_image'>{image}</span>";
                $fake_image = $post_thumb ? $post_thumb : $fake_image;
                $extra_class= $post_thumb ? "" : "related-format-visible";
                $parity     = $slidecount % 2 ? 'Odd' : 'Even';
                $insert_tooltip = $tooltip == true ? "data-avia-related-tooltip=\"". esc_attr( avia_wp_get_the_title( $related_post->ID ) ) . "\"" : "";

                $output .= "<div class='$post_class $extra relThumb relThumb{$count} relThumb{$parity} post-format-{$format} related_column'>\n";
                $output .= "    <a href='".get_permalink($related_post->ID)."' class='relThumWrap noLightbox' title='".esc_attr( avia_wp_get_the_title( $related_post->ID ) )."'>\n";
                $output .= "    <span class='related_image_wrap' {$insert_tooltip}>";
                $output .=      $image;
                $output .= "    <span class='related-format-icon {$extra_class}'><span class='related-format-icon-inner' ".av_icon_string($format)."></span></span>";
                $output .= "    </span>";
                $output .=      "<strong class='av-related-title'>" . avia_wp_get_the_title( $related_post->ID ) . "</strong>";
                $output .=      apply_filters('avf_related_post_loop', "", $related_post);
                $output .= "    </a>";
                $output .= "</div>";

                $count++;
                $extra = "";

                if($count == count($my_query)) $extra = 'omega';

            }


            $output .= "</div></div>";
            $output = str_replace("{image}",$fake_image,$output);

            if($related_posts) echo $output;

        }

        wp_reset_query();
    }
}