Using Assetic's Css Rewriter outside of Symfony - assetic

Question

Let me start by saying I have absolutely no idea what I should be doing because the documentation and available information on Assetic is either limited or Symfony oriented.
Here is my folder structure.
Assetic
+ assets
+ css
+ example.css
+ docs
+ src
+ tests
+ vendor
+ index.php
+ styles.php
Now, I have the following test code. Basically I cloned a clean copy of Assetic and ran composer install. Then I create an index.php file which simply links to my styles.php file with HTMLs <link> tag.
Here is my styles.php
<?php
require 'vendor/autoload.php';
$assetPath = __DIR__.'/assets/css/example.css';
$assetBasePath = __DIR__.'/assets/css';
$asset = new Assetic\Asset\FileAsset($assetPath, array(), $assetBasePath, 'example.css');
header('Content-Type: text/css');
$asset->setTargetPath(__DIR__);
echo $asset->dump(new Assetic\Filter\CssRewriteFilter);
Here is my example.css stylesheet.
body {
background-image: url('../img/background.png');
}
When I load up the styles.php in my browser I get the following output.
url('../img/background.png');
That's the same as the actual CSS. If I use the CSS URI Rewriter from Mr. Clay I get the expected output.
url('/Assetic/assets/img/background.png');
So what am I doing wrong with Assetic? I have no idea what paths I should be passing in and to where.
Thanks.

Answer 1

Just a pretty hard time with it, but finally (after reading the doc. of webassets, python library on which assetic is based) I won over the lack of documentation.
Here you go
<?php
require 'vendor/autoload.php';
$assetPath = __DIR__.'/assets/css/example.css';
$asset = new Assetic\Asset\FileAsset($assetPath, array(new Assetic\Filter\CssRewriteFilter), dirname($assetPath), '/assets/css');
// I assume the 'assets' directory is at the root of your website
header('Content-Type: text/css');
$asset->setTargetPath('/path/to/dumped/asset');
// As above, it's the path to the generated asset from your http root
echo $asset->dump();
I'm not sure to be very clear, so ask if you didn't understand something.