php给一张图片加上水印效果

 <?php
 /**
   * 功能：给一张图片加上水印效果
   *           $i  要加水印效果的图片
   *           $t  水印文字
   *           $size 文字大小
   *           $pos 水印的位置
   *            $color 文字的颜色
   *           $flag 是布尔值，主要用来区分是不是原图上加水印
   *           $type 如果$flag等于false 则新图上加上水印 新文件名为 原名_txt.jpg
   */
 function txt($i,$t='版权所有',$size=25,$pos=5,$color='rand',$flag=true,$type='_txt'){
     $img = imagecreatefromjpeg($i);
     $w = imagesx($img);
     $h = imagesy($img);
     $font = dirname(__FILE__).'/font/ls.ttf';
     $ps = imagettfbbox($size,0,$font,$t);
     $tw = $ps[4];
     $th = abs($ps[5]);
     switch($pos){
         case 1:break;
         case 2:break;
         case 3:break;
         case 4:break;
         case 5:$x=($w-$tw)/2;$y=($h-$th)/2+$th;break;
         case 6:break;
         case 7:break;
         case 8:break;
         case 9:break;
         default:break;
     }
     $c = getcolor($img,$color);
     imagettftext($img,$size,0,$x,$y,$c,$font,$t);
     if($flag){
         imagejpeg($img,$i);
     }else{
         $ext = ext($i);
         $ppp = rtrim($i,'.'.$ext);
         $ppp = $ppp.$type.'.'.$ext;
         imagejpeg($img,$ppp);
     }
 }

 function getcolor($i,$c='rand',$a=50){
     $cc = '';
     switch($c){
         case 'white':$cc=imagecolorallocatealpha($i,255,255,255,$a);break;
         case 'black':$cc=imagecolorallocatealpha($i,0,0,0,$a);break;
         case 'red':$cc=imagecolorallocatealpha($i,255,0,0,$a);break;
         case 'green':$cc=imagecolorallocatealpha($i,0,255,0,$a);break;
         case 'blue':$cc=imagecolorallocatealpha($i,0,0,255,$a);break;
         case 'orange':$cc=imagecolorallocatealpha($i,0xff,0x66,0x33,$a);break;
         case 'yellow':$cc=imagecolorallocatealpha($i,255,255,0,$a);break;
         case 'rand':$cc=imagecolorallocatealpha($i,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255),$a);break;
         default:
             $cs = substr($c,1);
             $ok = str_split($cs,2);
             $cc = imagecolorallocatealpha($i,hexdec($ok[0]),hexdec($ok[1]),hexdec($ok[2]),$a);
         break;
     }
     return $cc;
 }

 /**
  * 功能是：返回扩展名
  */

 function ext($f){
     $exts = explode('.',$f);
     return end($exts);
 }

 /**
   *  功能是：返回文件名，不含扩展名
   */
 function name($f){
     $s = explode('/',$f);
     $fn = end($s);
     return rtrim($fn,'.'.ext($f));
 }