Timer::just_finished() returns true forever when paused during finish tick

[Madadog]

Bevy version

0.6.1

Operating system & version

Ubuntu 20.04

The problem

The description of Timer::just_finished() claims it "returns true only on the tick the timer reached its duration", but pausing during that tick causes it to return true indefinitely. This causes inconsistent behaviour as it means pausing a timer will occasionally make Timer::just_finished() return true every frame, usually resulting in a massive speedup for anything the method is being used for: periodic entity spawning, advancing an animation, or printing info to the console.

It's possible this isn't actually a bug, but at the very least it leads to unintuitive behaviour which should be correctly indicated in the method's description.

Minimal example:

use bevy::prelude::*;
use std::time::Duration;

fn main() {
    // consistent for both repeating and non-repeating timers
    let mut timer = Timer::from_seconds(1.0, false);

    // finish timer
    timer.tick(Duration::from_secs_f32(1.0));
    assert!(timer.just_finished());
    
    // pause timer while just_finished()
    timer.pause();

    // timer is now just_finished() forever
    for _ in 0..100 {
        timer.tick(Duration::from_secs_f32(0.5));
        assert!(timer.just_finished());
    }
}

How was this found?

What you did

Used a timer to advance an animation when timer.just_finished() == true. Paused the timer.

What you expected to happen

The animation would stop.

What actually happened

The animation would stop unless it was paused on the tick timer.just_finished() == true. If this happened, the animation would speed up to the screen's refresh rate. Unpausing the animation would slow it back down.

Solutions you have considered

• Make tick() reset times_finished to 0 when paused
  • In general, ticking a paused timer is supposed to do nothing.
  • Need to consider what exactly times_finished means while paused / if anything relies on it not changing.

[Protowalker]

@alice-i-cecile this has since been fixed. Good to close?