/**
 * Implements template_preprocess_responsive_image().
 */
function webp_preprocess_responsive_image(&$variables) {
  $webp_sources = [];
  if (isset($variables['sources'])) {
    foreach ($variables['sources'] as $source) {
      /** @var \Drupal\Core\Template\Attribute $source */

      // Blazy module is using another srcset attribute.
      $srcset_attribute_key = FALSE;
      if ($source->offsetExists('data-srcset')) {
        $srcset_attribute_key = 'data-srcset';
      }
      elseif ($source->offsetExists('srcset')) {
        $srcset_attribute_key = 'srcset';
      }

      if ($srcset_attribute_key !== FALSE) {
        $srcset_orig = $source->offsetGet($srcset_attribute_key)->value();

        /* @var \Drupal\webp\Webp $webp */
        $webp = \Drupal::service('webp.webp');
        $webp_srcset = $webp->getWebpSrcset($srcset_orig);

+        // Create the Webp image if it doesn't exist.
+        $img_paths  = explode(', ', $srcset_orig);
+        $webp_paths = explode(', ', $webp_srcset);
+        foreach ($webp_paths as $key => $webp_path) {
+          $img_real_path  = explode(' ', $img_paths[$key]);
+          $img_real_path  = \Drupal::service('file_system')->realpath($img_real_path[0]);
+          $webp_real_path = explode(' ', $webp_path);
+          $webp_real_path = \Drupal::service('file_system')->realpath($webp_real_path[0]);
+          if (!file_exists($webp_real_path)) {
+            exec('/home/ciafcoma/bin/cwebp ' . $img_real_path . ' -o ' . $webp_real_path);
+          }
+        }

        // Create a new source pointing to the webp URL.
        $webp_source = clone $source;
        $webp_source->offsetSet($srcset_attribute_key, $webp_srcset);
        $webp_source->offsetSet('type', 'image/webp');
        $webp_sources[] = $webp_source;
      }
    }

    // Add the new sources at the top of the list.
-    $variables['sources'] = array_merge($webp_sources, $variables['sources']);
+    // $variables['sources'] = array_merge($webp_sources, $variables['sources']);
+
+    // Replace the sources if WebP is supported.
+    if (strpos($_SERVER['HTTP_ACCEPT'], 'image/webp') !== FALSE) {
+      $variables['sources'] = $webp_sources;
+    }

    // Never output a single image tag, because
    // we will always have at least two sources.
    $variables['output_image_tag'] = FALSE;
  }
}