我这样处理上下文：

function wpse_216001_srcset() {
    // generate your Srcset here and return 
}
function wpse_216001_sizes() {
    // generate your sizes attribute here and return
}

add_filter( \'wp_calculate_image_sizes\', \'wpse_216001_sizes\', 10 , 2 );
add_filter( \'wp_calculate_image_srcset\', \'wpse_216001_srcset\', 10 , 5);

// call one of the standard WP image output functions here

remove_filter( \'wp_calculate_image_sizes\', \'wpse_216001_sizes\', 10 );
remove_filter( \'wp_calculate_image_srcset\', \'wpse_216001_srcset\', 10 );