template_preprocess_image_style_preview

template_preprocess_image_style_preview(&$variables)

function template_preprocess_image_style_preview(&$variables) {
  // Style information.
  $style = $variables['style'];
  $variables['style_id'] = $style->id();
  $variables['style_name'] = $style->label();

  // Cache bypass token.
  $variables['cache_bypass'] = REQUEST_TIME;

  // Sample image info.
  $sample_width = 160;
  $sample_height = 160;
  $image_factory = \Drupal::service('image.factory');

  // Set up original file information.
  $original_path = \Drupal::config('image.settings')->get('preview_image');
  $original_image = $image_factory->get($original_path);
  $variables['original'] = array(
    'url' => file_url_transform_relative(file_create_url($original_path)),
    'width' => $original_image->getWidth(),
    'height' => $original_image->getHeight(),
  );
  if ($variables['original']['width'] > $variables['original']['height']) {
    $variables['preview']['original']['width'] = min($variables['original']['width'], $sample_width);
    $variables['preview']['original']['height'] = round($variables['preview']['original']['width'] / $variables['original']['width'] * $variables['original']['height']);
  }
  else {
    $variables['preview']['original']['height'] = min($variables['original']['height'], $sample_height);
    $variables['preview']['original']['width'] = round($variables['preview']['original']['height'] / $variables['original']['height'] * $variables['original']['width']);
  }

  // Set up derivative file information.
  $preview_file = $style->buildUri($original_path);
  // Create derivative if necessary.
  if (!file_exists($preview_file)) {
    $style->createDerivative($original_path, $preview_file);
  }
  $preview_image = $image_factory->get($preview_file);
  $variables['derivative'] = array(
    'url' => file_url_transform_relative(file_create_url($preview_file)),
    'width' => $preview_image->getWidth(),
    'height' => $preview_image->getHeight(),
  );
  if ($variables['derivative']['width'] > $variables['derivative']['height']) {
    $variables['preview']['derivative']['width'] = min($variables['derivative']['width'], $sample_width);
    $variables['preview']['derivative']['height'] = round($variables['preview']['derivative']['width'] / $variables['derivative']['width'] * $variables['derivative']['height']);
  }
  else {
    $variables['preview']['derivative']['height'] = min($variables['derivative']['height'], $sample_height);
    $variables['preview']['derivative']['width'] = round($variables['preview']['derivative']['height'] / $variables['derivative']['height'] * $variables['derivative']['width']);
  }

  // Build the preview of the original image.
  $variables['original']['rendered'] = array(
    '#theme' => 'image',
    '#uri' => $original_path,
    '#alt' => t('Sample original image'),
    '#title' => '',
    '#attributes' => array(
      'width' => $variables['original']['width'],
      'height' => $variables['original']['height'],
      'style' => 'width: ' . $variables['preview']['original']['width'] . 'px; height: ' . $variables['preview']['original']['height'] . 'px;',
    ),
  );

  // Build the preview of the image style derivative. Timestamps are added
  // to prevent caching of images on the client side.
  $variables['derivative']['rendered'] = array(
    '#theme' => 'image',
    '#uri' => $variables['derivative']['url'] . '?cache_bypass=' . $variables['cache_bypass'],
    '#alt' => t('Sample modified image'),
    '#title' => '',
    '#attributes' => array(
      'width' => $variables['derivative']['width'],
      'height' => $variables['derivative']['height'],
      'style' => 'width: ' . $variables['preview']['derivative']['width'] . 'px; height: ' . $variables['preview']['derivative']['height'] . 'px;',
    ),
  );

}