private void maybeOnImageShownImmediately() {
    if (!mOnFadeListenerShowImmediately) {
      return;
    }

    if (mTransitionState == TRANSITION_NONE && mIsLayerOn[mActualImageLayer]) {
      if (mOnFadeListener != null) {
        mOnFadeListener.onShownImmediately();
      }
      mOnFadeListenerShowImmediately = false;
    }
  }
Updates the current alphas based on the ratio of the elapsed time and duration.

@param ratio
@return whether the all layers have reached their target opacity
drawee/src/main/java/com/facebook/drawee/drawable/FadeDrawable.java