code: public void fadeUpToLayer(int index) {
      mTransitionState = TRANSITION_STARTING;
      Arrays.fill(mIsLayerOn, 0, index + 1, true);
      Arrays.fill(mIsLayerOn, index + 1, mLayers.length, false);
      invalidateSelf();
    }
docs: Starts fading up to the specified layer.
  <p>
  Layers up to the specified layer inclusive will fade in, other layers will fade out.
  @param index the index of the layer to fade up to.