add_filter('tc_core', 'use_custom_slider_class');
function use_custom_slider_class($classes){
    //don't instanciate default class
    unset( $classes['content'][
        array_search(array('inc/parts','slider'), $classes['content'])
        ]
    );
    //instanciate our class
    new TC_Slider_mod;
    return $classes;
}
add_filter('tc_slider_name_id', 'my_slider_of_posts');
function my_slider_of_posts( $slider_name_id ){
    if ( $slider_name_id == 'front-slider' )
        return array(
            'slider'    => 'front-slider',
            'query'     => array(
                'tag'            => "front-slider",
                'posts_per_page' => 5,
                'order'          => 'desc'
            )
        );
    return $slider_name_id;
}
define('CUSTOMIZR', get_template_directory() );
require_once( CUSTOMIZR . '/inc/parts/class-content-slider.php');
class TC_Slider_mod extends TC_slider{

    // override tc_get_slides
    function tc_get_slides($slider_name_id, $img_size){
        if ( ! is_array($slider_name_id) )
            return parent::tc_get_slides($slider_name_id, $img_size);

        // from here starts a slightly different version of the parent::tc_get_slides
        extract($slider_name_id);

        $all_sliders              = tc__f('__get_option' , 'tc_sliders');
        $saved_slides             = ( isset($all_sliders[$slider]) ) ? $all_sliders[$slider] : false;
        //if the slider not longer exists or exists but is empty, return false
        if ( !isset($saved_slides) || !is_array($saved_slides) || empty($saved_slides) )
            return;

        $posts = new WP_Query($query);

        // if you don't want to show the first attachment when featured image isn't set
        // remove the line below
        add_filter('tc_show_single_post_content', '__return_false');

        // build our array of slides

        //inititalize the slides array
        $slides = array();

        //init slide active state index
        $i      = 0;
        while ( $posts -> have_posts() ){
            $posts -> the_post();

            //title
            $title                  = get_the_title();
            $default_title_length   = apply_filters( 'tc_slide_title_length', 80 );
            $title                  = ( strlen($title) > $default_title_length ) ? substr( $title,0,strpos( $title, ' ' , $default_title_length) ). ' ...' : $title;
            //lead text
            $text                   = get_the_excerpt();
            $default_text_length    = apply_filters( 'tc_slide_text_length', 250 );
            $text                   = ( strlen($text) > $default_text_length ) ? substr( $text,0,strpos( $text, ' ' ,$default_text_length) ). ' ...' : $text;

            //button text
            $button_text            = __('Read more »', 'customizr');
            $default_button_length  = apply_filters( 'tc_slide_button_length', 80 );
            $button_text            = ( strlen($button_text) > $default_button_length ) ? substr( $button_text,0,strpos( $button_text, ' ' ,$default_button_length)). ' ...' : $button_text;

            //link post id
            $link_id                = get_the_id();

            $id                     = $link_id;
            //button link
            $link_url               = $link_id ? get_permalink( $link_id ) : 'javascript:void(0)';

            //sets the first slide active
            $active                 = ( 0 == $i ) ? 'active' : '';

            $color_style            = '';

            //attachment image
            $alt                    = apply_filters( 'tc_slide_background_alt' , trim(strip_tags( get_the_title() ) ) );
            $slide_background       = TC_post_thumbnails::$instance->tc_get_thumbnail_data($img_size)[0];
            //adds all values to the slide array only if the content exists (=> handle the case when an attachment has been deleted for example). Otherwise apply a default slide
            if ( empty($slide_background) )
                $slide_background   = wp_get_attachment_image( $saved_slides[1], $img_size, false, array( 'class' => 'slide' , 'alt' => $alt ) );

            $slides[$id]            = array(
                                    'title'               =>  $title,
                                    'text'                =>  $text,
                                    'button_text'         =>  $button_text,
                                    'link_id'             =>  $link_id,
                                    'link_url'            =>  $link_url,
                                    'active'              =>  $active,
                                    'color_style'         =>  $color_style,
                                    'slide_background'    =>  $slide_background,
            );

            //increments active index
            $i++;
        }//end of slides loop

        // if you chose to not show the first attachment when featured image isn't set
        // remove the line below
        remove_filter('tc_show_single_post_content', '__return_false');

        wp_reset_postdata();

        //returns the slides or false if nothing
        return ( !empty($slides) ) ? $slides : false;
    }
}