[Smush] - Fix srcset image sizes for better rendering

wpmudev-smush-cdn-sizes.php

<?php
/**
* Plugin Name: [Smush] - Fix srcset image sizes for better rendering
* Plugin URI: https://premium.wpmudev.org/
* Description: Extend existing functionality of Smush to provide appropriate responsive image sizes (as of 3.2.4)
* Author: Alessandro Kaounas @ WPMUDEV
* Author URI: https://premium.wpmudev.org/
* License: GPLv2 or later
*/

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

if ( ! class_exists( 'WPMUDEV_Smush_CDN_Sizes' ) ) {
    
    class WPMUDEV_Smush_CDN_Sizes {

        private static $_instance = null;

        public static function get_instance() {

            if( is_null( self::$_instance ) ){
                self::$_instance = new WPMUDEV_Smush_CDN_Sizes();
            }
            return self::$_instance;
            
        }

        private function __construct() {

            if ( class_exists( 'WP_Smush_Settings' ) ) {
                $this->settings = WP_Smush_Settings::get_instance();
            } elseif ( class_exists( '\\Smush\\Core\\Settings' ) ) {
                $this->settings = \Smush\Core\Settings::get_instance();
            } else {
                return;
            }

            $this->init();

        }

        private function init(){
            
            add_filter( 'wp_calculate_image_sizes', array( $this, 'wpmudev_update_image_sizes' ), 20, 5 );

        }

        public function wpmudev_update_image_sizes( $sizes, $size ) {
            // Get maximum content width.
            $content_width = $this->max_content_width();
    
            if ( is_array( $size ) && $size[0] < $content_width ) {
                return $sizes;
            }
    
            return sprintf( '(max-width: %1$dpx) 100vw, 100vw', $content_width );
        }

        private function max_content_width() {
            // Get global content width (if content width is empty, set 1900).
            $content_width = isset( $GLOBALS['content_width'] ) ? $GLOBALS['content_width'] : 1900;
    
            // Check to see if we are resizing the images (can not go over that value).
            $resize_sizes = $this->settings->get_setting( WP_SMUSH_PREFIX . 'resize_sizes' );
    
            if ( isset( $resize_sizes['width'] ) && $resize_sizes['width'] < $content_width ) {
                return $resize_sizes['width'];
            }
    
            // Just in case something goes wrong with the above checks.
            if ( ! $content_width ) {
                $content_width = 1900;
            }
    
            return $content_width;
        }

      
	}
	
    if ( ! function_exists( 'WPMUDEV_Smush_CDN_Sizes' ) ) {
        
        function WPMUDEV_Smush_CDN_Sizes() {
            return WPMUDEV_Smush_CDN_Sizes::get_instance();
        };

        add_action( 'plugins_loaded', 'WPMUDEV_Smush_CDN_Sizes', 99 );

    }

}