基于PHP服务端图片生成缩略图的方法详解

<?php
//定义缩略图片尺寸
$picsize = array(
              '100_100'=> 1,
              '200_100'=> 1
           );
$imagepath = "../image/";
function parseurl($url){
   preg_match("/(?p<name>[\w\d]+)_w(?p<width>\d+)_h(?p<height>\d+)\.(?p<ext>\w+)/",$url,$match);
   return $match;
}
$urlarr = explode("/",$_server['request_uri']);
$imgname = $urlarr[count($urlarr)-1];
$picinfo = parseurl($imgname);
//错误尺寸
if(empty($picinfo['width']) || empty($picinfo['height']) ||
!array_key_exists($picinfo['width'].'_'.$picinfo['height'],$picsize)) die('不存在该尺寸图片');
$originalpic = $imagepath.$picinfo['name'].'/'.$picinfo['name'].'.'.$picinfo['ext'];
//原始图不存在
if(!file_exists($originalpic)) die("图片不存在！");
/**
 *等比例压缩图片
 */
switch($picinfo['ext']){
   case 'jpg':
      $orgimg = imagecreatefromjpeg($originalpic);
      break;
   default:
      break;
}
$owidth  =  imagesx($orgimg); //原始尺寸
$oheight =  imagesy($orgimg);
$tw = $picinfo['width'];
$th = $picinfo['height'];
//获取缩略图尺寸
if($owidth/$oheight > $tw/$th){
    $th = intval($tw * $oheight/$owidth);
}else{
     $tw = intval($th * $owidth/$oheight);
}
//生成背景图
$new_img = imagecreatetruecolor($picinfo['width'], $picinfo['height']);
$bgcolor = imagecolorallocate($new_img,255,255,255);
if (!@imagefilledrectangle($new_img, 0, 0, $picinfo['width']-1, $picinfo['height']-1, $bgcolor)) {
    echo "无法创建背景图";  //@todo记录日志
    exit(0);
}
if (!@imagecopyresampled($new_img, $orgimg, ($picinfo['width']-$tw)/2, ($picinfo['height']-$th)/2, 0, 0, $tw, $th, $owidth, $oheight)) {
    echo "生成图片失败";
    exit(0);
}
//生成图片
ob_start();
imagejpeg($new_img);
$_newimg = ob_get_contents();
ob_end_clean();
file_put_contents($imagepath.$picinfo['name']."/".$imgname, $_newimg);
header("content-type:image/jpeg; charset=utf-8");
imagejpeg($new_img);
?>