Automatic Display Name

<?php
// Change the default display name in WordPress
// http://www.simplewptricks.com
if ( is_user_logged_in() ) {
    global $current_user;
    get_currentuserinfo();
    $swpt_username = $current_user->user_login ;
    $swpt_firstname = $current_user->user_firstname ;
    $swpt_lastname = $current_user->user_lastname ;
    $swpt_displayname = $current_user->display_name ;

    if ( empty($swpt_firstname) && empty($swpt_lastname)) {
        $new_display_name = $swpt_username; }
    elseif ( !empty($swpt_firstname) && empty($swpt_lastname)) {
        $new_display_name = $swpt_firstname; }
    elseif ( empty($swpt_firstname) && !empty($swpt_lastname)) {
        $new_display_name = $swpt_lastname; }
    elseif ( !empty($swpt_firstname) && !empty($swpt_lastname)) {
        $new_display_name = $swpt_firstname . " " . $swpt_lastname; }
    else {}

    if ( $swpt_displayname != $new_display_name) {
        update_user_meta($current_user->ID, 'display_name', $new_display_name);    }
    else {}
}
?>