# 2015-05-04 mes notes à 
# source: http://www.stephanemartinw.com/articles/20-images-responsives-srcset-sizes-drupal

function generate_image($source, $dest, $styles) {
    if (!file_exists($dest)) {
        //on charge le style demandé
        $display_style = image_style_load($styles);

        //on retourne l'image créée
        return image_style_create_derivative($display_style, $source, $dest);
    }
    else return true;
}