ImageStyleEditForm::form

public ImageStyleEditForm::form(array $form, FormStateInterface $form_state)

public function form(array $form, FormStateInterface $form_state) {
  $user_input = $form_state->getUserInput();
  $form['#title'] = $this->t('Edit style %name', array('%name' => $this->entity->label()));
  $form['#tree'] = TRUE;
  $form['#attached']['library'][] = 'image/admin';

  // Show the thumbnail preview.
  $preview_arguments = array('#theme' => 'image_style_preview', '#style' => $this->entity);
  $form['preview'] = array(
    '#type' => 'item',
    '#title' => $this->t('Preview'),
    '#markup' => drupal_render($preview_arguments),
    // Render preview above parent elements.
    '#weight' => -5,
  );

  // Build the list of existing image effects for this image style.
  $form['effects'] = array(
    '#type' => 'table',
    '#header' => array(
      $this->t('Effect'),
      $this->t('Weight'),
      $this->t('Operations'),
    ),
    '#tabledrag' => array(
      array(
        'action' => 'order',
        'relationship' => 'sibling',
        'group' => 'image-effect-order-weight',
      ),
    ),
    '#attributes' => array(
      'id' => 'image-style-effects',
    ),
    '#empty' => t('There are currently no effects in this style. Add one by selecting an option below.'),
    // Render effects below parent elements.
    '#weight' => 5,
  );
  foreach ($this->entity->getEffects() as $effect) {
    $key = $effect->getUuid();
    $form['effects'][$key]['#attributes']['class'][] = 'draggable';
    $form['effects'][$key]['#weight'] = isset($user_input['effects']) ? $user_input['effects'][$key]['weight'] : NULL;
    $form['effects'][$key]['effect'] = array(
      '#tree' => FALSE,
      'data' => array(
        'label' => array(
          '#plain_text' => $effect->label(),
        ),
      ),
    );

    $summary = $effect->getSummary();

    if (!empty($summary)) {
      $summary['#prefix'] = ' ';
      $form['effects'][$key]['effect']['data']['summary'] = $summary;
    }

    $form['effects'][$key]['weight'] = array(
      '#type' => 'weight',
      '#title' => $this->t('Weight for @title', array('@title' => $effect->label())),
      '#title_display' => 'invisible',
      '#default_value' => $effect->getWeight(),
      '#attributes' => array(
        'class' => array('image-effect-order-weight'),
      ),
    );

    $links = array();
    $is_configurable = $effect instanceof ConfigurableImageEffectInterface;
    if ($is_configurable) {
      $links['edit'] = array(
        'title' => $this->t('Edit'),
        'url' => Url::fromRoute('image.effect_edit_form', [
          'image_style' => $this->entity->id(),
          'image_effect' => $key,
        ]),
      );
    }
    $links['delete'] = array(
      'title' => $this->t('Delete'),
      'url' => Url::fromRoute('image.effect_delete', [
        'image_style' => $this->entity->id(),
        'image_effect' => $key,
      ]),
    );
    $form['effects'][$key]['operations'] = array(
      '#type' => 'operations',
      '#links' => $links,
    );
  }

  // Build the new image effect addition form and add it to the effect list.
  $new_effect_options = array();
  $effects = $this->imageEffectManager->getDefinitions();
  uasort($effects, function($a, $b) {
    return strcasecmp($a['id'], $b['id']);
  });
  foreach ($effects as $effect => $definition) {
    $new_effect_options[$effect] = $definition['label'];
  }
  $form['effects']['new'] = array(
    '#tree' => FALSE,
    '#weight' => isset($user_input['weight']) ? $user_input['weight'] : NULL,
    '#attributes' => array('class' => array('draggable')),
  );
  $form['effects']['new']['effect'] = array(
    'data' => array(
      'new' => array(
        '#type' => 'select',
        '#title' => $this->t('Effect'),
        '#title_display' => 'invisible',
        '#options' => $new_effect_options,
        '#empty_option' => $this->t('Select a new effect'),
      ),
      array(
        'add' => array(
          '#type' => 'submit',
          '#value' => $this->t('Add'),
          '#validate' => array('::effectValidate'),
          '#submit' => array('::submitForm', '::effectSave'),
        ),
      ),
    ),
    '#prefix' => '<div class="image-style-new">',
    '#suffix' => '</div>',
  );

  $form['effects']['new']['weight'] = array(
    '#type' => 'weight',
    '#title' => $this->t('Weight for new effect'),
    '#title_display' => 'invisible',
    '#default_value' => count($this->entity->getEffects()) + 1,
    '#attributes' => array('class' => array('image-effect-order-weight')),
  );
  $form['effects']['new']['operations'] = array(
    'data' => array(),
  );

  return parent::form($form, $form_state);
}