Migrating stacked states to bevy 0.10

[chrishulbert]

Hi, My code followed an example that used stacked states to create a fade-to-black-then-fade-in transition effect between states: It would push a 'fading' state which would allow the old state to remain visible however it would not receive user input during the fade, and replace the whole stack with the new state after it reached the black in the middle of the transition.

Now that we cannot push states however, i'm not sure how to implement this neatly, any suggestions?

Here's my 0.9 code: https://github.com/chrishulbert/rusty-lemmings/blob/9e34441e2103d2aedb8cad5c4681f075dfe963a3/src/fadeout.rs#L53

Here's my 0.10 version so far: https://github.com/chrishulbert/rusty-lemmings/blob/master/src/fadeout.rs

The problem is that my 0.10 version still allows interaction with the old screen. It'd be nice to disable the old screens without having to update every screen of my app to have a flag whereby it ignores user input after initiating a fade.

Any suggestions hugely appreciated, thanks for the great work :)

[chrishulbert]

So the way i implemented this was to create an 'is transitioning' resource, set to true at the start, and false at the end of the transition. Then I created a 'run condition' system like so:

// To be used as a run condition using 'run_if' for any interaction system you want disabled
// while transitioning.
pub fn screen_fade_is_not_transitioning(is_transitioning: Res<ScreenFadeIsTransitioning>) -> bool {
    !is_transitioning.0
}

And finally, in all the screens that used transitions, i added a run_if to the applicable systems that I did not want to run during transition, eg the mouse input ones, like this:

        app.add_systems((
            button_system.run_if(screen_fade_is_not_transitioning),
        ).in_set(OnUpdate(GameState::LevelPreview)));

This is a lot more code than it was in bevy 0.9, i wonder if there's a better way? I guess it doesn't matter much. And probably worth it to simplify bevy and get rid of the stacked states - they were super complex, i understand the motivation to remove them :)