Get all tags based on specific category (including all tags from child categories and posts) wordpress

Question

I wanted to use wp_tag_cloud() on single.php using the argument that gets all tags from specific category including all tags from its child categories and posts.

Answer 1

I am getting closer on this.

<div class="tag_cloud_on_single">

    <h2>Popular Topics</h2>

    <?php

    $category = get_the_category();
    $root_cat_of_curr =  $category[0]->category_parent;

    function get_cat_slug($cat_id) {
        $cat_id = (int) $cat_id;
        $category = &get_category($cat_id);
        return $category->slug;
    }

    $my_cat = get_cat_slug($root_cat_of_curr);

    $custom_query = new WP_Query('posts_per_page=-1&category_name='.$my_cat.'');
    if ($custom_query->have_posts()) :
        while ($custom_query->have_posts()) : $custom_query->the_post();
            $posttags = get_the_tags();
            if ($posttags) {
                foreach($posttags as $tag) {
                    $all_tags[] = $tag->term_id;
                }
            }
        endwhile;
    endif;

    $tags_arr = array_unique($all_tags);
    $tags_str = implode(",", $tags_arr);

    $args = array(
        'smallest'                  => 12, 
        'largest'                   => 24,
        'unit'                      => 'pt', 
        'number'                    => 0,  
        'format'                    => 'flat',
        'separator'                 => "&nbsp;&nbsp;&nbsp;",
        'orderby'                   => 'name', 
        'order'                     => 'RAND',
        'exclude'                   => null,  
        'topic_count_text_callback' => default_topic_count_text,
        'link'                      => 'view', 
        'echo'                      => true,
        'include'                   => $tags_str
    );

    wp_tag_cloud($args);

    ?>

</div>

Thanks all for your contribution. Appreciate your help.