PHP实现圆角图片

工作中用到，自己写了一个，分享给有需要的人，前面是类定义，后面2行是调用。
优点：
不需要外部图片
支持PNG透明
可自定义圆角半径
不足：
只能指定一种透明色
 <?php
class RoundedCorner {
private $_r;
private $_g;
private $_b;
private $_image_path;
private $_radius;

function __construct($image_path, $radius, $r = 255, $g = 0, $b = 0) {
$this->_image_path = $image_path;
$this->_radius = $radius;
$this->_r = (int)$r;
$this->_g = (int)$g;
$this->_b = (int)$b;
}

private function _get_lt_rounder_corner() {
$radius = $this->_radius;
$img = imagecreatetruecolor($radius, $radius);
$bgcolor = imagecolorallocate($img, $this->_r, $this->_g, $this->_b);
$fgcolor = imagecolorallocate($img, 0, 0, 0);
imagefill($img, 0, 0, $bgcolor);
imagefilledarc($img, $radius, $radius, $radius*2, $radius*2, 180, 270, $fgcolor, IMG_ARC_PIE);
imagecolortransparent($img, $fgcolor);
return $img;
}

private function _load_source_image() {
$ext = substr($this->_image_path, strrpos($this->_image_path, '.'));
if (empty($ext)) {
return false;
}
switch(strtolower($ext)) {
case '.jpg':
$img = @imagecreatefromjpeg($this->_image_path);
break;
case '.gif':
$img = @imagecreatefromgif($this->_image_path);
break;
case '.png':
$img = @imagecreatefrompng($this->_image_path);
break;
default:
return false;
}
return $img;

}

public function round_it() {
// load the source image
$src_image = $this->_load_source_image();
if ($src_image === false) {
die('Sorry, can\'t load the image');
}
$image_width = imagesx($src_image);
$image_height = imagesy($src_image);

// create a new image, with src_width, src_height, and fill it with transparent color
$image = imagecreatetruecolor($image_width, $image_height);
$trans_color = imagecolorallocate($image, $this->_r, $this->_g, $this->_b