Pausing the virtual clock stops event updates.

[brandon-reinhart]

Bevy version

0.14

What you did

It could be I don't understand the intent behind Time<Virtual>. I thought it was meant as a gameplay clock separate from the wall clock in Time<Real>.

There is a footgun for games that want to use Time<Virtual> but which do not use a fixed update. If you pause Time<Virtual> then the FixedUpdate schedule does not run. If the FixedUpdate schedule does not run, events do not get updated.

This is because the TimePlugin, by default, sets the event updates to happen on the next FixedUpdate.

If you use events for UI, for example, and pause your game by pausing Time<Virtual> those events will start to accumulate until read or the game is unpaused. This is unexpected.

A game that doesn't want to use the FixedUpdate, but still wants to use Time<Virtual> for gametime and pausing must do this:

    let mut event_registry = app
        .world_mut()
        .resource_mut::<bevy::ecs::event::EventRegistry>();
    event_registry.should_update = ShouldUpdateEvents::Always;

What to do?

Maybe TimePlugin should have configuration to select the event update strategy. However, I think that FixedUpdate games that pause the clock will be surprised by events accumulating? Or maybe Time<Virtual> is not intended to be used as a gameplay clock, just as pacing for FixedUpdate?

[brandon-reinhart]

It could be intended that events are not dropped, but this probably needs to be more clearly documented somewhere. It means that systems that use events and can run when the game is paused need to be structured differently to account for the possibility of old events (like effectively buffered keyboard input, etc).

[alice-i-cecile]

This is my doing; my changes to how the signalling worked must have subtly broken this use case.

[brandon-reinhart]

People can do this in the mean time:

let mut event_registry = app
        .world_mut()
        .resource_mut::<bevy::ecs::event::EventRegistry>();
    event_registry.should_update = ShouldUpdateEvents::Always;

Do that after you register TimePlugin but before you run()

[alice-i-cecile]

Because there's a workaround, I'm going to bump this to 0.15. Getting a proper fix in is quite involved, and made much more painful to backport due to a refactor in how the event code is organized.