Draw a string vertically in PHP

<?php//  w  ww .  jav a 2 s . co  m
// create a 100*100 image
$im = imagecreatetruecolor(100, 100);

// Write the text
$textcolor = imagecolorallocate($im, 0xFF, 0xFF, 0xFF);
imagestringup($im, 3, 40, 80, 'gd library', $textcolor);

// Save the image
imagepng($im, './stringup.png');
imagedestroy($im);
?>