How to preserve transparency in PHP GD on a PNG

[hax0r2]

I am using this code:\[code\] <?phplist($width, $height, $type, $attr) = getimagesize("terrain.png"); $canvas = imagecreatetruecolor($width, $height);$src = http://stackoverflow.com/questions/3746140/imagecreatefrompng("terrain.png");if($_GET['glass'] == 1){$src2 = imagecreatefrompng("rock.png");}imagecopymerge($canvas, $src, 0, 0, 0, 0, $width, $height, 100);if($_GET['glass'] == 1){imagecopy($canvas, $src2, 0, 0, 0, 0, 16, 16);}imagealphablending($canvas, true);imagesavealpha($canvas, true); header("Content-type: image/png"); imagepng($canvas); imagedestroy($dest);imagedestroy($src);?>\[/code\]Terrain.png is at http://hogofwar.co.uk/experiment/mc/terrain.png (which is transparent)How do I preserve the transparency when using GD?