php将图片切成圆角

public function test($url,$path='./uploads/maphead/',$uid){  
        $w = 30;  $h=30; // original size  
        $original_path= $url;
        //$urltime=uniqid();
        $dest_path = $path.$uid.'.png';  
        $headurl=$uid.'.png';
        $src = imagecreatefromstring(file_get_contents($original_path));  
        $newpic = imagecreatetruecolor($w,$h);  
        imagealphablending($newpic,false);  
        $transparent = imagecolorallocatealpha($newpic, 0, 0, 0, 130);  
        $r=$w/2;  
        for($x=0;$x<$w;$x++)  
            for($y=0;$y<$h;$y++){  
                $c = imagecolorat($src,$x,$y);  
                $_x = $x - $w/2;  
                $_y = $y - $h/2;  
                if((($_x*$_x) + ($_y*$_y)) < ($r*$r)){  
                    imagesetpixel($newpic,$x,$y,$c);  
                }else{  
                    imagesetpixel($newpic,$x,$y,$transparent);  
                }  
            }  
        imagesavealpha($newpic, true);  
        imagepng($newpic, $dest_path);  
        imagedestroy($newpic);  
        imagedestroy($src);
}