Improve timer ergonomics. Add tests (#923)

crates/bevy_core/src/time/timer.rs

@@ -9,8 +9,11 @@ use bevy_utils::Duration;
 /// Repeating timers will only be in the finished state on each tick `duration` is reached or exceeded, and can still be reset at any given point.
 #[derive(Clone, Debug, Default, Properties)]
 pub struct Timer {
+    /// Time elapsed on the timer. Guaranteed to be between 0.0 and `duration`, inclusive.
     pub elapsed: f32,
     pub duration: f32,
+    /// Non repeating timers will stop tracking and stay in the finished state until reset.
+    /// Repeating timers will only be in the finished state on each tick `duration` is reached or exceeded, and can still be reset at any given point.
     pub finished: bool,
     /// Will only be true on the tick `duration` is reached or exceeded.
     pub just_finished: bool,
@@ -36,16 +39,19 @@ impl Timer {
 
     /// Advances the timer by `delta` seconds.
     pub fn tick(&mut self, delta: f32) -> &Self {
-        let prev_finished = self.elapsed >= self.duration;
+        let prev_finished = self.finished;
-        if !prev_finished {
+        self.elapsed += delta;
-            self.elapsed += delta;
-        }
 
         self.finished = self.elapsed >= self.duration;
         self.just_finished = !prev_finished && self.finished;
-
+        if self.finished {
-        if self.repeating && self.finished {
+            if self.repeating {
-            self.elapsed %= self.duration;
+                // Repeating timers wrap around
+                self.elapsed %= self.duration;
+            } else {
+                // Non-repeating timers clamp to duration
+                self.elapsed = self.duration;
+            }
         }
         self
     }
@@ -55,6 +61,16 @@ impl Timer {
         self.just_finished = false;
         self.elapsed = 0.0;
     }
+
+    /// Percent timer has elapsed (goes from 0.0 to 1.0)
+    pub fn percent(&self) -> f32 {
+        self.elapsed / self.duration
+    }
+
+    /// Percent left on timer (goes from 1.0 to 0.0)
+    pub fn percent_left(&self) -> f32 {
+        (self.duration - self.elapsed) / self.duration
+    }
 }
 
 pub(crate) fn timer_system(time: Res<Time>, mut query: Query<&mut Timer>) {
@@ -62,3 +78,64 @@ pub(crate) fn timer_system(time: Res<Time>, mut query: Query<&mut Timer>) {
         timer.tick(time.delta_seconds);
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::Timer;
+
+    #[test]
+    fn test_non_repeating() {
+        let mut t = Timer::from_seconds(10.0, false);
+        // Tick once, check all attributes
+        t.tick(0.25);
+        assert_eq!(t.elapsed, 0.25);
+        assert_eq!(t.duration, 10.0);
+        assert_eq!(t.finished, false);
+        assert_eq!(t.just_finished, false);
+        assert_eq!(t.repeating, false);
+        assert_eq!(t.percent(), 0.025);
+        assert_eq!(t.percent_left(), 0.975);
+        // Tick past the end and make sure elapsed doesn't go past 0.0 and other things update
+        t.tick(500.0);
+        assert_eq!(t.elapsed, 10.0);
+        assert_eq!(t.finished, true);
+        assert_eq!(t.just_finished, true);
+        assert_eq!(t.percent(), 1.0);
+        assert_eq!(t.percent_left(), 0.0);
+        // Continuing to tick when finished should only change just_finished
+        t.tick(1.0);
+        assert_eq!(t.elapsed, 10.0);
+        assert_eq!(t.finished, true);
+        assert_eq!(t.just_finished, false);
+        assert_eq!(t.percent(), 1.0);
+        assert_eq!(t.percent_left(), 0.0);
+    }
+
+    #[test]
+    fn test_repeating() {
+        let mut t = Timer::from_seconds(2.0, true);
+        // Tick once, check all attributes
+        t.tick(0.75);
+        assert_eq!(t.elapsed, 0.75);
+        assert_eq!(t.duration, 2.0);
+        assert_eq!(t.finished, false);
+        assert_eq!(t.just_finished, false);
+        assert_eq!(t.repeating, true);
+        assert_eq!(t.percent(), 0.375);
+        assert_eq!(t.percent_left(), 0.625);
+        // Tick past the end and make sure elapsed wraps
+        t.tick(1.5);
+        assert_eq!(t.elapsed, 0.25);
+        assert_eq!(t.finished, true);
+        assert_eq!(t.just_finished, true);
+        assert_eq!(t.percent(), 0.125);
+        assert_eq!(t.percent_left(), 0.875);
+        // Continuing to tick should turn off both finished & just_finished for repeating timers
+        t.tick(1.0);
+        assert_eq!(t.elapsed, 1.25);
+        assert_eq!(t.finished, false);
+        assert_eq!(t.just_finished, false);
+        assert_eq!(t.percent(), 0.625);
+        assert_eq!(t.percent_left(), 0.375);
+    }
+}