PHP GD Help Please

[xface]

A friend wrote this code for me and it works in my application but the thumbnails that are displayed look stretched. I don't know how to do it but would like the images to be resized to just a width, keeping the hieght ratio intact. So like if I want my thumbs to be 133px wide, the height is adjusted automatically and the image isnt stretched. Here is the code:
[code]
function createthumbs($name,$filename,$new_w,$new_h)
{
global $extension;

if(extension_loaded("gd2") || extension_loaded("gd")) {
if($extension == "jpeg" || $extension == "jpg" || $extension == "gif" || $extension == "png"){
$system=explode(".",$name);
if($extension == "jpeg" || $extension == "jpg"){
$src_img=imagecreatefromjpeg($name);
}
if($extension == "png"){
$src_img=imagecreatefrompng($name);
}
if($extension == "gif"){
$src_img=imagecreatefromgif($name);
}
    $old_x=imageSX($src_img);
      $old_y=imageSY($src_img);
        $thumb_w=$new_w;
        $thumb_h=$new_h;
    $dst_img=ImageCreateTrueColor($thumb_w,$thumb_h);
    imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y);
if ($extension == "png"){
        imagepng($dst_img,$filename);
    } else {
        imagejpeg($dst_img,$filename);
    }
    imagedestroy($dst_img);
    imagedestroy($src_img);
}
}
}
[/code]

Any help would be greatly appreciated!
Thanks.

[EKINdesigns]

Give this a try:

[code=php:0]if(($thumb_w < $old_x)){
$aspect_ratio = $thumb_w / $old_x;
$height = round($old_y * $aspect_ratio);
$width = $old_x;
}[/code]

[xface]

[quote author=EKINdesigns link=topic=121215.msg498056#msg498056 date=1168074647]
Give this a try:

[code=php:0]if(($thumb_w < $old_x)){
$aspect_ratio = $thumb_w / $old_x;
$height = round($old_y * $aspect_ratio);
$width = $old_x;
}[/code]
[/quote]

Cool, I pasted this to my exsisting code and now I get a fat red x. LOL I been playing around with it for a half hour changing this and that with no luck. Where would this code be pasted for it to work properly in the above code?