CThemeManager

public function getBasePath()
{
    if($this->_basePath===null)
        $this->setBasePath(dirname(Yii::app()->getRequest()->getScriptFile()).DIRECTORY_SEPARATOR.self::DEFAULT_BASEPATH);
    return $this->_basePath;
}

public function getBaseUrl()
{
    if($this->_baseUrl===null)
        $this->_baseUrl=Yii::app()->getBaseUrl().'/'.self::DEFAULT_BASEPATH;
    return $this->_baseUrl;
}

public function getTheme($name)
{
    $themePath=$this->getBasePath().DIRECTORY_SEPARATOR.$name;
    if(is_dir($themePath))
    {
        $class=Yii::import($this->themeClass, true);
        return new $class($name,$themePath,$this->getBaseUrl().'/'.$name);
    }
    else
        return null;
}

public function getThemeNames()
{
    static $themes;
    if($themes===null)
    {
        $themes=array();
        $basePath=$this->getBasePath();
        $folder=@opendir($basePath);
        while(($file=@readdir($folder))!==false)
        {
            if($file!=='.' && $file!=='..' && $file!=='.svn' && $file!=='.gitignore' && is_dir($basePath.DIRECTORY_SEPARATOR.$file))
                $themes[]=$file;
        }
        closedir($folder);
        sort($themes);
    }
    return $themes;
}

public function setBasePath($value)
{
    $this->_basePath=realpath($value);
    if($this->_basePath===false || !is_dir($this->_basePath))
        throw new CException(Yii::t('yii','Theme directory "{directory}" does not exist.',array('{directory}'=>$value)));
}

public function setBaseUrl($value)
{
    $this->_baseUrl=rtrim($value,'/');
}