EditorImageDialog::buildForm

public EditorImageDialog::buildForm(array $form, FormStateInterface $form_state, Editor $editor = NULL)

public function buildForm(array $form, FormStateInterface $form_state, Editor $editor = NULL) {
  // This form is special, in that the default values do not come from the
  // server side, but from the client side, from a text editor. We must cache
  // this data in form state, because when the form is rebuilt, we will be
  // receiving values from the form, instead of the values from the text
  // editor. If we don't cache it, this data will be lost.
  if (isset($form_state->getUserInput()['editor_object'])) {
    // By convention, the data that the text editor sends to any dialog is in
    // the 'editor_object' key. And the image dialog for text editors expects
    // that data to be the attributes for an <img> element.
    $image_element = $form_state->getUserInput()['editor_object'];
    $form_state->set('image_element', $image_element);
    $form_state->setCached(TRUE);
  }
  else {
    // Retrieve the image element's attributes from form state.
    $image_element = $form_state->get('image_element') ? : [];
  }

  $form['#tree'] = TRUE;
  $form['#attached']['library'][] = 'editor/drupal.editor.dialog';
  $form['#prefix'] = '<div id="editor-image-dialog-form">';
  $form['#suffix'] = '</div>';

  // Construct strings to use in the upload validators.
  $image_upload = $editor->getImageUploadSettings();
  if (!empty($image_upload['max_dimensions']['width']) || !empty($image_upload['max_dimensions']['height'])) {
    $max_dimensions = $image_upload['max_dimensions']['width'] . 'x' . $image_upload['max_dimensions']['height'];
  }
  else {
    $max_dimensions = 0;
  }
  $max_filesize = min(Bytes::toInt($image_upload['max_size']), file_upload_max_size());

  $existing_file = isset($image_element['data-entity-uuid']) ? \Drupal::entityManager()->loadEntityByUuid('file', $image_element['data-entity-uuid']) : NULL;
  $fid = $existing_file ? $existing_file->id() : NULL;

  $form['fid'] = array(
    '#title' => $this->t('Image'),
    '#type' => 'managed_file',
    '#upload_location' => $image_upload['scheme'] . '://' . $image_upload['directory'],
    '#default_value' => $fid ? array($fid) : NULL,
    '#upload_validators' => array(
      'file_validate_extensions' => array('gif png jpg jpeg'),
      'file_validate_size' => array($max_filesize),
      'file_validate_image_resolution' => array($max_dimensions),
    ),
    '#required' => TRUE,
  );

  $form['attributes']['src'] = array(
    '#title' => $this->t('URL'),
    '#type' => 'textfield',
    '#default_value' => isset($image_element['src']) ? $image_element['src'] : '',
    '#maxlength' => 2048,
    '#required' => TRUE,
  );

  // If the editor has image uploads enabled, show a managed_file form item,
  // otherwise show a (file URL) text form item.
  if ($image_upload['status']) {
    $form['attributes']['src']['#access'] = FALSE;
    $form['attributes']['src']['#required'] = FALSE;
  }
  else {
    $form['fid']['#access'] = FALSE;
    $form['fid']['#required'] = FALSE;
  }

  // The alt attribute is *required*, but we allow users to opt-in to empty
  // alt attributes for the very rare edge cases where that is valid by
  // specifying two double quotes as the alternative text in the dialog.
  // However, that *is* stored as an empty alt attribute, so if we're editing
  // an existing image (which means the src attribute is set) and its alt
  // attribute is empty, then we show that as two double quotes in the dialog.
  // @see https://www.drupal.org/node/2307647
  $alt = isset($image_element['alt']) ? $image_element['alt'] : '';
  if ($alt === '' && !empty($image_element['src'])) {
    $alt = '""';
  }
  $form['attributes']['alt'] = array(
    '#title' => $this->t('Alternative text'),
    '#placeholder' => $this->t('Short description for the visually impaired'),
    '#type' => 'textfield',
    '#required' => TRUE,
    '#required_error' => $this->t('Alternative text is required.<br />(Only in rare cases should this be left empty. To create empty alternative text, enter <code>""</code> — two double quotes without any content).'),
    '#default_value' => $alt,
    '#maxlength' => 2048,
  );

  // When Drupal core's filter_align is being used, the text editor may
  // offer the ability to change the alignment.
  if (isset($image_element['data-align']) && $editor->getFilterFormat()->filters('filter_align')->status) {
    $form['align'] = array(
      '#title' => $this->t('Align'),
      '#type' => 'radios',
      '#options' => array(
        'none' => $this->t('None'),
        'left' => $this->t('Left'),
        'center' => $this->t('Center'),
        'right' => $this->t('Right'),
      ),
      '#default_value' => $image_element['data-align'] === '' ? 'none' : $image_element['data-align'],
      '#wrapper_attributes' => array('class' => array('container-inline')),
      '#attributes' => array('class' => array('container-inline')),
      '#parents' => array('attributes', 'data-align'),
    );
  }

  // When Drupal core's filter_caption is being used, the text editor may
  // offer the ability to in-place edit the image's caption: show a toggle.
  if (isset($image_element['hasCaption']) && $editor->getFilterFormat()->filters('filter_caption')->status) {
    $form['caption'] = array(
      '#title' => $this->t('Caption'),
      '#type' => 'checkbox',
      '#default_value' => $image_element['hasCaption'] === 'true',
      '#parents' => array('attributes', 'hasCaption'),
    );
  }

  $form['actions'] = array(
    '#type' => 'actions',
  );
  $form['actions']['save_modal'] = array(
    '#type' => 'submit',
    '#value' => $this->t('Save'),
    // No regular submit-handler. This form only works via JavaScript.
    '#submit' => array(),
    '#ajax' => array(
      'callback' => '::submitForm',
      'event' => 'click',
    ),
  );

  return $form;
}