PHP GD Arrows

<?php
header("Content-type: image/png");
$im = imagecreate(400, 400);


$bg = imagecolorallocate($im, 255, 255, 255);

$red = imagecolorallocate($im, 255, 0, 0);

$points = array(5,             0,         0,                   5        ,       10           ,               5);
                              //up    start point                           final point
$num = count($points) / 2;


imagepolygon($im, $points, $num, $red);
imagefilledpolygon($im, $points, $num, $red);


imagepng($im);
imagedestroy($im);
?>