setGradientMapTransitionPhase(phase) {
    if (this._gradientMapTransitionPhase != phase) {
      this._gradientMapTransitionPhase = phase;
      this._gradientMapDirty = true;
    }
  }
Sets the 0.0 to 1.0 amount of the gradient color map from/to transition.
@param     {Number}     phase   Value of 0.0 to 1.0 of the period / phase of the transition from one to other color map.