Does Flutter render un-seenable content?

I have two containers each containing their own stateful widgets, overlapping each other in a stack.

Both stateful widgets in the containers may be updated async anytime.

Container(
  height: double.infinity,
  width: double.infinity,
  child: Stack(
    children: [
      Container(
        height: double.infinity,
        width: double.infinity,
        color: Colors.red,
        child: <some stateful widget 1>,
      ), //container 1
      Container(
        height: double.infinity,
        width: double.infinity,
        color: Colors.green,
        child: <some stateful widget 2>,
      ), //container 2
    ),
  ),
);

I want to use an animation controller to control the opacities of container 1 and container 2 such that container 1 fades out (opacity from 1.0 to 0.0) and container 2 then fades in (opacity from 0.0 to 1.0).

I have 2 questions:

  1. I would like to confirm if that there is none, or negligible rendering cost if setState is called for container 2 while container 2 opacity is 0

  2. Supposing that container 1 and container 2 overlaps fully, container 1 on top and container 2 bottom, will setState cause unnecessary rendering of container 2 when it's called?