docs: function () {
              var thisOption = this.option;
  
              return zrUtil.bind(
                  thisOption.mappingMethod === 'category'
                      ? function (value, isNormalized) {
                          !isNormalized && (value = this._normalizeData(value));
                          return doMapCategory.call(this, value);
                      }
                      : function (value, isNormalized, out) {
                          // If output rgb array
                          // which will be much faster and useful in pixel manipulation
                          var returnRGBArray = !!out;
                          !isNormalized && (value = this._normalizeData(value));
                          out = zrColor.fastLerp(value, thisOption.parsedVisual, out);
                          return returnRGBArray ? out : zrColor.stringify(out, 'rgba');
                      },
                  this
              );
          }