CssOptimizer::processFile

protected CssOptimizer::processFile($css_asset)

protected function processFile($css_asset) {
  $contents = $this->loadFile($css_asset['data'], TRUE);

  $contents = $this->clean($contents);

  // Get the parent directory of this file, relative to the Drupal root.
  $css_base_path = substr($css_asset['data'], 0, strrpos($css_asset['data'], '/'));
  // Store base path.
  $this->rewriteFileURIBasePath = $css_base_path . '/';

  // Anchor all paths in the CSS with its base URL, ignoring external and absolute paths.
  return preg_replace_callback('/url\(\s*[\'"]?(?![a-z]+:|\/+)([^\'")]+)[\'"]?\s*\)/i', array($this, 'rewriteFileURI'), $contents);
}