How can I display fullname as username ?

/** @var disUser $disUser */
$disUser = $modx->getObject('disUser',array(
   'user' => $modx->user->get('id'),
));

/* GetFullname snippet */
$output = '';
$uid = $modx->user->get('id');
$profile = $modx->getObject('modUserProfile', array('internalKey' => $uid));
if ($profile) {
    $output = $profile->get('fullname');
}
return $output;

/* GetFullname snippet (faster version) */
$output = '';
$uid = $modx->user->get('id');

$query = $modx->newQuery('modUserProfile', array(
    'internalKey' => $uid,
));
$query->select('fullname');
return $modx->getValue($query->prepare());

[[!+modx.user.id:userinfo=`fullname`]]

/**
     * Initializes the user, tracks their ip and activity, and loads their
     * profile. Also loads topbar information and links.
     *
     * @access private
     */
    private function _initUser() {
        $this->modx->lexicon->load('discuss:default');
        /* if no user, set id to 0 */
        $isLoggedIn = $this->modx->user->hasSessionContext($this->modx->context->get('key'));
        if (!$isLoggedIn) {
            $this->user = $this->modx->newObject('disUser');
            $this->user->set('id',0);
            $this->user->set('user',0);
            $this->user->set('username','(anonymous)');
            $this->user->isLoggedIn = false;
        } else {
            /* we are logged into MODX, check for user in Discuss */
            $this->user = $this->modx->getObject('disUser',array('user' => $this->modx->user->get('id')));
            if (empty($this->user)) {
                /* if no disUser exists but there is a modUser, import! */
                $profile = $this->modx->user->getOne('Profile');

                $this->user = $this->modx->newObject('disUser');
                $this->user->fromArray(array(
                    'user' => $this->modx->user->get('id'),
                    'username' => $this->modx->user->get('username'),
                    'password' => $this->modx->user->get('password'),
                    'salt' => $this->modx->user->get('salt'),
                    'synced' => true,
                    'syncedat' => date('Y-m-d H:I:S'),
                    'confirmed' => true,
                    'confirmedon' => date('Y-m-d H:I:S'),
                    'source' => 'internal',
                    'ip' => $this->getIp(),
                    'status' => disUser::ACTIVE,
                ));
                if ($profile) {
                    $this->user->fromArray($profile->toArray());
                    $fullname = $profile->get('fullname');
                    $name = $profile->get('fullname');
                    $name = explode(' ',$name);
                    $this->user->fromArray(array(
                        'name_first' => $name[0],
                        'name_last' => isset($name[1]) ? $name[1] : '',
                    ));
                }
                $this->user->save();
            }
            $this->user->init();
        }
    }

'username' => $profile->get('fullname'),