onScaleUpdate method
Implementation
void onScaleUpdate(double rotation, double scale) {
if (_rotationState == RotationState.uninitialized &&
rotation.abs() > rotationDeadzone) {
_rotationState = RotationState.enabled;
}
if (_rotationState == RotationState.uninitialized &&
(scale - 1.0).abs() > scaleDeadzone) {
_rotationState = RotationState.disabled;
}
}