framework/web/AssetConverter.php
public function convert($asset, $basePath)
    {
        $pos = strrpos($asset, '.');
        if ($pos !== false) {
            $ext = substr($asset, $pos + 1);
            if (isset($this->commands[$ext])) {
                list($ext, $command) = $this->commands[$ext];
                $result = substr($asset, 0, $pos + 1) . $ext;
                if ($this->forceConvert || @filemtime("$basePath/$result") < @filemtime("$basePath/$asset")) {
                    $this->runCommand($command, $basePath, $asset, $result);
                }

                return $result;
            }
        }

        return $asset;
    }
public function convert($asset, $basePath)
    {
        $pos = strrpos($asset, '.');
        if ($pos !== false) {
            $ext = substr($asset, $pos + 1);
            if (isset($this->commands[$ext])) {
                list($ext, $command) = $this->commands[$ext];
                $result = substr($asset, 0, $pos + 1) . $ext;
                if ($this->forceConvert || @filemtime("$basePath/$result") < @filemtime("$basePath/$asset")) {
                    $this->runCommand($command, $basePath, $asset, $result);
                }

                return $result;
            }
        }

        return $asset;
    }
Converts a given asset file into a CSS or JS file.
@param string $asset the asset file path, relative to $basePath
@param string $basePath the directory the $asset is relative to.
@return string the converted asset file path, relative to $basePath.