PHP自定义图片缩放函数实现等比例不失真缩放的方法

function resizeimage($im,$maxwidth,$maxheight,$name,$filetype)
{
  $pic_width = imagesx($im);
  $pic_height = imagesy($im);

  if(($maxwidth && $pic_width > $maxwidth) || ($maxheight && $pic_height > $maxheight))
  {
    if($maxwidth && $pic_width>$maxwidth)
    {
      $widthratio = $maxwidth/$pic_width;
      $resizewidth_tag = true;
    }

    if($maxheight && $pic_height>$maxheight)
    {
      $heightratio = $maxheight/$pic_height;
      $resizeheight_tag = true;
    }

    if($resizewidth_tag && $resizeheight_tag)
    {
      if($widthratio<$heightratio)
        $ratio = $widthratio;
      else
        $ratio = $heightratio;
    }

    if($resizewidth_tag && !$resizeheight_tag)
      $ratio = $widthratio;
    if($resizeheight_tag && !$resizewidth_tag)
      $ratio = $heightratio;

    $newwidth = $pic_width * $ratio;
    $newheight = $pic_height * $ratio;

    if(function_exists("imagecopyresampled"))
    {
      $newim = imagecreatetruecolor($newwidth,$newheight);
      imagecopyresampled($newim,$im,0,0,0,0,$newwidth,$newheight,$pic_width,$pic_height);
    }
    else
    {
      $newim = imagecreate($newwidth,$newheight);
      imagecopyresized($newim,$im,0,0,0,0,$newwidth,$newheight,$pic_width,$pic_height);
    }

    $name = $name.$filetype;
    imagejpeg($newim,$name);
    imagedestroy($newim);
  }
  else
  {
    $name = $name.$filetype;
    imagejpeg($im,$name);
  }
}