bool offstage

Whether this route is currently offstage.

On the first frame of a route's entrance transition, the route is built Offstage using an animation progress of 1.0. The route is invisible and non-interactive, but each widget has its final size and position. This mechanism lets the HeroController determine the final local of any hero widgets being animated as part of the transition.

Source 

bool get offstage => _offstage;
void offstage=(bool value)

Source 

set offstage (bool value) {
  if (_offstage == value)
    return;
  setState(() {
    _offstage = value;
  });
  _animationProxy.parent = _offstage ? kAlwaysCompleteAnimation : super.animation;
  _forwardAnimationProxy.parent = _offstage ? kAlwaysDismissedAnimation : super.forwardAnimation;
}