php创建缩略图程序

function Thumb_IM($thumbwidth, $thumbheight, $preview = 0) {
  global $thumbstatus, $imageimpath, $thumbquality;
  if($thumbstatus) {
   list($img_w, $img_h) = $this->attachinfo;
   $targetfile = !$preview ? ($thumbstatus == 1 || $thumbstatus == 3 ? $this->targetfile.'.thumb.jpg' : $this->targetfile) : DISCUZ_ROOT.'./forumdata/watermark_temp.jpg';
   if(!$this->animatedgif && ($img_w >= $thumbwidth || $img_h >= $thumbheight)) {
    if($thumbstatus != 3) {
     $exec_str = $imageimpath.'/convert -quality '.intval($thumbquality).' -geometry '.$thumbwidth.'x'.$thumbheight.' '.$this->targetfile.' '.$targetfile;
     @exec($exec_str, $output, $return);
     if(empty($return) && empty($output)) {
      $this->attach['thumb'] = $thumbstatus == 1 ? 1 : 0;
     }
    } else {
     $imgratio = $img_w / $img_h;
     $thumbratio = $thumbwidth / $thumbheight;
     if($imgratio >= 1 && $imgratio >= $thumbratio || $imgratio < 1 && $imgratio > $thumbratio) {
      $cuty = $img_h;
      $cutx = $cuty * $thumbratio;
     } elseif($imgratio >= 1 && $imgratio <= $thumbratio || $imgratio < 1 && $imgratio < $thumbratio) {
      $cutx = $img_w;
      $cuty = $cutx / $thumbratio;
     }
     $exec_str = $imageimpath.'/convert -crop '.$cutx.'x'.$cuty.'+0+0  '.$this->targetfile.' '.$targetfile;
     @exec($exec_str, $output, $return);
     $exec_str = $imageimpath.'/convert -quality '.intval($thumbquality).' -geometry '.$thumbwidth.'x'.$thumbheight.' '.$targetfile.' '.$targetfile;
     @exec($exec_str, $output, $return);
     if(empty($return) && empty($output)) {
      $this->attach['thumb'] = $thumbstatus == 1 || $thumbstatus == 3 ? 1 : 0;
     }
    }
             }
  }
 }