docs: public void setOpacity(int opacity) {
  		mBarPointerPosition = Math.round((mOpacToPosFactor * opacity))
  				+ mBarPointerHaloRadius;
  		calculateColor(mBarPointerPosition);
  		mBarPointerPaint.setColor(mColor);
  		if (mPicker != null) {
  			mPicker.setNewCenterColor(mColor);
  		}
  		invalidate();
  	}