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));
}