Pass URL to form

Hi,

I found this code snippet here http://www.gravityhelp.com/forums/topic/use-postpage-title-for-subject.

1- Add the Post Title field to your form
a- Allow it to be populated dynamically (advanced tab)
b- Type "posttitle" in the "parameter name" text field

2- Add the following code snippet to your template's functions.php file

[php]
add_filter('gform_field_value_posttitle', 'populate_post_title');
function populate_post_title(){
global $post;
return $post->post_title;
}

It works great, but I dont know how to get the post URL instead of post title. Can somewho I do that?