php简单实用生成缩略图代码

$w?$resizewidth=$w:$resizewidth=400;// 生成图片的宽度
$h?$resizeheight=$h:$resizeheight=400;// 生成图片的高度
function resizeimage($im,$maxwidth,$maxheight,$name){
$width = imagesx($im);
$height = imagesy($im);
if(($maxwidth && $width > $maxwidth) || ($maxheight && $height > $maxheight)){
if($maxwidth && $width > $maxwidth){
$widthratio = $maxwidth/$width;
$resizewidth=true;
}
if($maxheight && $height > $maxheight){
$heightratio = $maxheight/$height;
$resizeheight=true;
}
if($resizewidth && $resizeheight){
if($widthratio < $heightratio){
$ratio = $widthratio;
}else{
$ratio = $heightratio;
}
}elseif($resizewidth){
$ratio = $widthratio;
}elseif($resizeheight){
$ratio = $heightratio;
}
$newwidth = $width * $ratio;
$newheight = $height * $ratio;
if(function_exists("imagecopyresampled")){
$newim = imagecreatetruecolor($newwidth, $newheight);
imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
}else{
$newim = imagecreate($newwidth, $newheight);
imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
}
imagejpeg ($newim,$name);
imagedestroy ($newim);
}else{
imagejpeg ($im,$name);
}
}

if($_files['uploadfile']['size']){
if($_files['uploadfile']['type'] == "image/pjpeg"){
$im = imagecreatefromjpeg($_files['uploadfile']['tmp_name']);
}elseif($_files['uploadfile']['type'] == "image/x-png"){
$im = imagecreatefrompng($_files['uploadfile']['tmp_name']);
}elseif($_files['uploadfile']['type'] == "image/gif"){
$im = imagecreatefromgif($_files['uploadfile']['tmp_name']);
}
if($im){
if(file_exists('bbs.jpg')){
unlink('bbs.jpg');
}
resizeimage($im,$resizewidth,$resizeheight,'bbs.jpg');
imagedestroy ($im);

}
}
//$uploadfile="www.111com.net.jpg";
?>