@Override
public void onScale(GestureHandler.ScaleEvent event) {
float scaleFactorDelta = event.getScaleFactorDelta();
float scalePointX = event.getScalePointX();
float scalePointY = event.getScalePointY();
// updates ImageViewer and ViewController on scale event
updateUiAndTvScale(scaleFactorDelta, scalePointX, scalePointY);
}
