function setStop(value, valueState) {
            stops.push({
                value: value,
                color: getColorVisual(value, valueState)
            });
        }
@param {module:echarts/component/visualMap/VisualMapModel} visualMapModel\
@param {module:echarts/ExtensionAPI} api
@param {Array.<number>} itemSize always [short, long]
@return {string} 'left' or 'right' or 'top' or 'bottom'