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));
}