public function getEffectParamsList($effectParams)
    {
        if ($this->_effectParamsList === null) {
            // see if the the effect defintion contains a vars key
            if (!array_key_exists('vars', $effectParams)) {
                throw new Exception("Required 'vars' key not found in effect definition array.");
            }

            foreach ($effectParams['vars'] as $item) {
                $this->_effectParamsList[] = $item['var'];
            }
        }

        return $this->_effectParamsList;
    }