php 图片上添加透明度渐变的效果

<?php 
////$strimgsrc = file_get_contents("http://127.0.0.1/5307754.jpg"); 
////$imgsrc = imagecreatefromstring($strimgsrc); 
$imgsrc = imagecreatefromjpeg("5307754.jpg"); 
$imgsrcw = imagesx($imgsrc); 
$imgsrch = imagesy($imgsrc); 
$width = 30; 
$x1 = 2; 
$x2 = $imgsrcw - $x1 - 20; 
$y1 = ($imgsrch - $width) - 2; 
$y2 = $y1 + $width; 
$steps = $x2 - $x1; 
for($i = 0; $i < $steps; $i ++) 
{ 
$alphax = round($i/($steps/127))+60; 
if($alphax >= 128) 
$alphax = 127; 
$alpha = imagecolorallocatealpha($imgsrc, 255, 255, 255, $alphax); 
imagefilledrectangle($imgsrc, ($i+$x1), $y1, ($i+$x1+1), $y2, $alpha); 
} 
header('content-type: image/jpeg'); 
imagejpeg($imgsrc); 
imagedestroy($imgsrc); 
?>