drupal 7, display add entity form in ctools popup.

cba_events.module

/**
 * Create default entity in ctools popup.
 */
function cba_events_create_default_entity_in_popup($js, $user_id) {
  if (!$js) {
    return drupal_goto('event/default/add');
  }

  ctools_include('ajax');
  ctools_include('modal');
  ctools_modal_add_js();

  $entity = entity_create('event', array('type' => 'default'));
  $form_state = array(
    'ajax' => TRUE,
    'title' => t('Add default event'),
    'build_info' => array(
      'args' => array($entity),
    ),
  );
  $form = ctools_modal_form_wrapper('eck__entity__form_add_event_default', $form_state);

  if (!empty($form_state['executed'])) {
    $commands = array();
    $commands[] = global_ajax_command_reload();
    print ajax_render($commands);
    drupal_exit();
  }

  print ajax_render($form);
  drupal_exit();
}