From 097a55948cf85aae1c9cd35503155a41e032803e Mon Sep 17 00:00:00 2001
From: Amber Kowalski <amberkowalski03@gmail.com>
Date: Sat, 28 Nov 2020 16:08:31 -0500
Subject: [PATCH] Refactor Time API and internals (#934)

Refactor Time API and internals
---
 CHANGELOG.md                                  |   9 ++
 crates/bevy_core/src/time/time.rs             | 119 ++++++++++++++++--
 .../src/frame_time_diagnostics_plugin.rs      |   4 +-
 .../src/print_diagnostics_plugin.rs           |   4 +-
 examples/2d/contributors.rs                   |   4 +-
 examples/2d/sprite_sheet.rs                   |   2 +-
 examples/3d/parenting.rs                      |   2 +-
 examples/3d/spawner.rs                        |   4 +-
 examples/3d/z_sort_debug.rs                   |   2 +-
 examples/app/plugin.rs                        |   2 +-
 examples/ecs/event.rs                         |   2 +-
 examples/ecs/hierarchy.rs                     |   8 +-
 examples/ecs/timers.rs                        |   6 +-
 examples/game/breakout.rs                     |   4 +-
 examples/tools/bevymark.rs                    |   8 +-
 examples/ui/font_atlas_debug.rs               |   2 +-
 examples/wasm/winit_wasm.rs                   |   2 +-
 examples/window/window_settings.rs            |   2 +-
 18 files changed, 146 insertions(+), 40 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 05e7dbaaebd89..9783fb107eb6b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,9 +13,18 @@ current changes on git with [previous release tags][git_tag_comparison].
 
 ### Changed
 - [Breaking changes to timer API][914]
+  - Created getters and setters rather than exposing struct members.
 - [Removed timer auto-ticking system][931]
+  - Added an example of how to tick timers manually.
+- [Breaking changes to Time API][934]
+  - Created getters to get `Time` state and made members private.
+  - Modifying `Time`'s values directly is no longer possible outside of bevy.
 ### Fixed
 
+[914]: https://github.com/bevyengine/bevy/pull/914
+[931]: https://github.com/bevyengine/bevy/pull/931
+[934]: https://github.com/bevyengine/bevy/pull/934
+
 
 ## Version 0.3.0 (2020-11-03)
 
diff --git a/crates/bevy_core/src/time/time.rs b/crates/bevy_core/src/time/time.rs
index 0baee828e2bf0..d2f32411bceef 100644
--- a/crates/bevy_core/src/time/time.rs
+++ b/crates/bevy_core/src/time/time.rs
@@ -4,19 +4,19 @@ use bevy_utils::{Duration, Instant};
 /// Tracks elapsed time since the last update and since the App has started
 #[derive(Debug)]
 pub struct Time {
-    pub delta: Duration,
-    pub instant: Option<Instant>,
-    pub delta_seconds_f64: f64,
-    pub delta_seconds: f32,
-    pub seconds_since_startup: f64,
-    pub startup: Instant,
+    delta: Duration,
+    last_update: Option<Instant>,
+    delta_seconds_f64: f64,
+    delta_seconds: f32,
+    seconds_since_startup: f64,
+    startup: Instant,
 }
 
 impl Default for Time {
     fn default() -> Time {
         Time {
             delta: Duration::from_secs(0),
-            instant: None,
+            last_update: None,
             startup: Instant::now(),
             delta_seconds_f64: 0.0,
             seconds_since_startup: 0.0,
@@ -28,15 +28,55 @@ impl Default for Time {
 impl Time {
     pub fn update(&mut self) {
         let now = Instant::now();
-        if let Some(instant) = self.instant {
-            self.delta = now - instant;
+        self.update_with_instant(now);
+    }
+
+    pub(crate) fn update_with_instant(&mut self, instant: Instant) {
+        if let Some(last_update) = self.last_update {
+            self.delta = instant - last_update;
             self.delta_seconds_f64 = self.delta.as_secs_f64();
             self.delta_seconds = self.delta.as_secs_f32();
         }
 
-        let duration_since_startup = now - self.startup;
+        let duration_since_startup = instant - self.startup;
         self.seconds_since_startup = duration_since_startup.as_secs_f64();
-        self.instant = Some(now);
+        self.last_update = Some(instant);
+    }
+
+    /// The delta between the current tick and last tick as a [`Duration`]
+    #[inline]
+    pub fn delta(&self) -> Duration {
+        self.delta
+    }
+
+    /// The delta between the current and last tick as [`f32`] seconds
+    #[inline]
+    pub fn delta_seconds(&self) -> f32 {
+        self.delta_seconds
+    }
+
+    /// The delta between the current and last tick as [`f64`] seconds
+    #[inline]
+    pub fn delta_seconds_f64(&self) -> f64 {
+        self.delta_seconds_f64
+    }
+
+    /// The time since startup in seconds
+    #[inline]
+    pub fn seconds_since_startup(&self) -> f64 {
+        self.seconds_since_startup
+    }
+
+    /// The [`Instant`] the app was started
+    #[inline]
+    pub fn startup(&self) -> Instant {
+        self.startup
+    }
+
+    /// The ['Instant'] when [`Time::update`] was last called, if it exists
+    #[inline]
+    pub fn last_update(&self) -> Option<Instant> {
+        self.last_update
     }
 
     pub fn time_since_startup(&self) -> Duration {
@@ -47,3 +87,60 @@ impl Time {
 pub(crate) fn time_system(mut time: ResMut<Time>) {
     time.update();
 }
+
+#[cfg(test)]
+mod tests {
+    use super::Time;
+    use bevy_utils::{Duration, Instant};
+
+    #[test]
+    fn update_test() {
+        let start_instant = Instant::now();
+
+        // Create a `Time` for testing
+        let mut time = Time {
+            startup: start_instant,
+            ..Default::default()
+        };
+
+        // Ensure `time` was constructed correctly
+        assert_eq!(time.delta(), Duration::from_secs(0));
+        assert_eq!(time.last_update(), None);
+        assert_eq!(time.startup(), start_instant);
+        assert_eq!(time.delta_seconds_f64(), 0.0);
+        assert_eq!(time.seconds_since_startup(), 0.0);
+        assert_eq!(time.delta_seconds(), 0.0);
+
+        // Update `time` and check results
+        let first_update_instant = Instant::now();
+
+        time.update_with_instant(first_update_instant);
+
+        assert_eq!(time.delta(), Duration::from_secs(0));
+        assert_eq!(time.last_update(), Some(first_update_instant));
+        assert_eq!(time.startup(), start_instant);
+        assert_eq!(time.delta_seconds_f64(), 0.0);
+        assert_eq!(
+            time.seconds_since_startup(),
+            (first_update_instant - start_instant).as_secs_f64()
+        );
+        assert_eq!(time.delta_seconds, 0.0);
+
+        // Update `time` again and check results
+        let second_update_instant = Instant::now();
+
+        time.update_with_instant(second_update_instant);
+
+        assert_eq!(time.delta(), second_update_instant - first_update_instant);
+        assert_eq!(time.last_update(), Some(second_update_instant));
+        assert_eq!(time.startup(), start_instant);
+        // At this point its safe to use time.delta as a valid value
+        // because it's been previously verified to be correct
+        assert_eq!(time.delta_seconds_f64(), time.delta().as_secs_f64());
+        assert_eq!(
+            time.seconds_since_startup(),
+            (second_update_instant - start_instant).as_secs_f64()
+        );
+        assert_eq!(time.delta_seconds(), time.delta().as_secs_f32());
+    }
+}
diff --git a/crates/bevy_diagnostic/src/frame_time_diagnostics_plugin.rs b/crates/bevy_diagnostic/src/frame_time_diagnostics_plugin.rs
index aaabf1b6ac700..628a37104a9f7 100644
--- a/crates/bevy_diagnostic/src/frame_time_diagnostics_plugin.rs
+++ b/crates/bevy_diagnostic/src/frame_time_diagnostics_plugin.rs
@@ -40,11 +40,11 @@ impl FrameTimeDiagnosticsPlugin {
         state.frame_count += 1.0;
         diagnostics.add_measurement(Self::FRAME_COUNT, state.frame_count);
 
-        if time.delta_seconds_f64 == 0.0 {
+        if time.delta_seconds_f64() == 0.0 {
             return;
         }
 
-        diagnostics.add_measurement(Self::FRAME_TIME, time.delta_seconds_f64);
+        diagnostics.add_measurement(Self::FRAME_TIME, time.delta_seconds_f64());
         if let Some(fps) = diagnostics
             .get(Self::FRAME_TIME)
             .and_then(|frame_time_diagnostic| {
diff --git a/crates/bevy_diagnostic/src/print_diagnostics_plugin.rs b/crates/bevy_diagnostic/src/print_diagnostics_plugin.rs
index 2d9d077a78405..9587b2290e446 100644
--- a/crates/bevy_diagnostic/src/print_diagnostics_plugin.rs
+++ b/crates/bevy_diagnostic/src/print_diagnostics_plugin.rs
@@ -66,7 +66,7 @@ impl PrintDiagnosticsPlugin {
         time: Res<Time>,
         diagnostics: Res<Diagnostics>,
     ) {
-        if state.timer.tick(time.delta_seconds).finished() {
+        if state.timer.tick(time.delta_seconds()).finished() {
             println!("Diagnostics:");
             println!("{}", "-".repeat(93));
             if let Some(ref filter) = state.filter {
@@ -86,7 +86,7 @@ impl PrintDiagnosticsPlugin {
         time: Res<Time>,
         diagnostics: Res<Diagnostics>,
     ) {
-        if state.timer.tick(time.delta_seconds).finished() {
+        if state.timer.tick(time.delta_seconds()).finished() {
             println!("Diagnostics (Debug):");
             println!("{}", "-".repeat(93));
             if let Some(ref filter) = state.filter {
diff --git a/examples/2d/contributors.rs b/examples/2d/contributors.rs
index 49889567099f7..80d13ad3dda93 100644
--- a/examples/2d/contributors.rs
+++ b/examples/2d/contributors.rs
@@ -217,7 +217,7 @@ fn deselect(
 
 /// Applies gravity to all entities with velocity
 fn velocity_system(time: Res<Time>, mut q: Query<Mut<Velocity>>) {
-    let delta = time.delta_seconds;
+    let delta = time.delta_seconds();
 
     for mut v in q.iter_mut() {
         v.translation += Vec3::new(0.0, GRAVITY * delta, 0.0);
@@ -274,7 +274,7 @@ fn collision_system(
 
 /// Apply velocity to positions and rotations.
 fn move_system(time: Res<Time>, mut q: Query<(&Velocity, Mut<Transform>)>) {
-    let delta = time.delta_seconds;
+    let delta = time.delta_seconds();
 
     for (v, mut t) in q.iter_mut() {
         t.translation += delta * v.translation;
diff --git a/examples/2d/sprite_sheet.rs b/examples/2d/sprite_sheet.rs
index 9b1b3e2c999ea..b2c7dc002b381 100644
--- a/examples/2d/sprite_sheet.rs
+++ b/examples/2d/sprite_sheet.rs
@@ -14,7 +14,7 @@ fn animate_sprite_system(
     mut query: Query<(&mut Timer, &mut TextureAtlasSprite, &Handle<TextureAtlas>)>,
 ) {
     for (mut timer, mut sprite, texture_atlas_handle) in query.iter_mut() {
-        timer.tick(time.delta_seconds);
+        timer.tick(time.delta_seconds());
         if timer.finished() {
             let texture_atlas = texture_atlases.get(texture_atlas_handle).unwrap();
             sprite.index = ((sprite.index as usize + 1) % texture_atlas.textures.len()) as u32;
diff --git a/examples/3d/parenting.rs b/examples/3d/parenting.rs
index a1125e5762df5..3df2f753c1df4 100644
--- a/examples/3d/parenting.rs
+++ b/examples/3d/parenting.rs
@@ -17,7 +17,7 @@ struct Rotator;
 /// rotates the parent, which will result in the child also rotating
 fn rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<Rotator>>) {
     for mut transform in query.iter_mut() {
-        transform.rotation *= Quat::from_rotation_x(3.0 * time.delta_seconds);
+        transform.rotation *= Quat::from_rotation_x(3.0 * time.delta_seconds());
     }
 }
 
diff --git a/examples/3d/spawner.rs b/examples/3d/spawner.rs
index 20a7552bc43df..ae5f1cba768ea 100644
--- a/examples/3d/spawner.rs
+++ b/examples/3d/spawner.rs
@@ -25,9 +25,9 @@ fn move_cubes(
 ) {
     for (mut transform, material_handle) in query.iter_mut() {
         let material = materials.get_mut(material_handle).unwrap();
-        transform.translation += Vec3::new(1.0, 0.0, 0.0) * time.delta_seconds;
+        transform.translation += Vec3::new(1.0, 0.0, 0.0) * time.delta_seconds();
         material.albedo =
-            Color::BLUE * Vec3::splat((3.0 * time.seconds_since_startup as f32).sin());
+            Color::BLUE * Vec3::splat((3.0 * time.seconds_since_startup() as f32).sin());
     }
 }
 
diff --git a/examples/3d/z_sort_debug.rs b/examples/3d/z_sort_debug.rs
index 73cc3c4ea5ec6..7b590579ccaf6 100644
--- a/examples/3d/z_sort_debug.rs
+++ b/examples/3d/z_sort_debug.rs
@@ -21,7 +21,7 @@ struct Rotator;
 /// rotates the parent, which will result in the child also rotating
 fn rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<Rotator>>) {
     for mut transform in query.iter_mut() {
-        transform.rotation *= Quat::from_rotation_x(3.0 * time.delta_seconds);
+        transform.rotation *= Quat::from_rotation_x(3.0 * time.delta_seconds());
     }
 }
 
diff --git a/examples/app/plugin.rs b/examples/app/plugin.rs
index d11b54f5d58a3..a220755c191f6 100644
--- a/examples/app/plugin.rs
+++ b/examples/app/plugin.rs
@@ -38,7 +38,7 @@ struct PrintMessageState {
 }
 
 fn print_message_system(mut state: ResMut<PrintMessageState>, time: Res<Time>) {
-    if state.timer.tick(time.delta_seconds).finished() {
+    if state.timer.tick(time.delta_seconds()).finished() {
         println!("{}", state.message);
     }
 }
diff --git a/examples/ecs/event.rs b/examples/ecs/event.rs
index c1ec889165dce..33cc3230dd513 100644
--- a/examples/ecs/event.rs
+++ b/examples/ecs/event.rs
@@ -34,7 +34,7 @@ fn event_trigger_system(
     mut state: ResMut<EventTriggerState>,
     mut my_events: ResMut<Events<MyEvent>>,
 ) {
-    if state.event_timer.tick(time.delta_seconds).finished() {
+    if state.event_timer.tick(time.delta_seconds()).finished() {
         my_events.send(MyEvent {
             message: "MyEvent just happened!".to_string(),
         });
diff --git a/examples/ecs/hierarchy.rs b/examples/ecs/hierarchy.rs
index 03fe54830f170..ed7a7c5242359 100644
--- a/examples/ecs/hierarchy.rs
+++ b/examples/ecs/hierarchy.rs
@@ -97,24 +97,24 @@ fn rotate(
     let angle = std::f32::consts::PI / 2.0;
     for (parent, children) in parents_query.iter_mut() {
         if let Ok(mut transform) = transform_query.get_mut(parent) {
-            transform.rotate(Quat::from_rotation_z(-angle * time.delta_seconds));
+            transform.rotate(Quat::from_rotation_z(-angle * time.delta_seconds()));
         }
 
         // To iterate through the entities children, just treat the Children component as a Vec
         // Alternatively, you could query entities that have a Parent component
         for child in children.iter() {
             if let Ok(mut transform) = transform_query.get_mut(*child) {
-                transform.rotate(Quat::from_rotation_z(angle * 2.0 * time.delta_seconds));
+                transform.rotate(Quat::from_rotation_z(angle * 2.0 * time.delta_seconds()));
             }
         }
 
         // To demonstrate removing children, we'll start to remove the children after a couple of seconds
-        if time.seconds_since_startup >= 2.0 && children.len() == 3 {
+        if time.seconds_since_startup() >= 2.0 && children.len() == 3 {
             let child = children.last().copied().unwrap();
             commands.despawn(child);
         }
 
-        if time.seconds_since_startup >= 4.0 {
+        if time.seconds_since_startup() >= 4.0 {
             // This will remove the entity from its parent's list of children, as well as despawn
             // any children the entity has.
             commands.despawn_recursive(parent);
diff --git a/examples/ecs/timers.rs b/examples/ecs/timers.rs
index 22ffff1e6be4d..14b17e27ebf69 100644
--- a/examples/ecs/timers.rs
+++ b/examples/ecs/timers.rs
@@ -39,7 +39,7 @@ fn setup_system(commands: &mut Commands) {
 /// using bevy's `Time` resource to get the delta between each update.
 fn timer_system(time: Res<Time>, mut query: Query<&mut Timer>) {
     for mut timer in query.iter_mut() {
-        if timer.tick(time.delta_seconds).just_finished() {
+        if timer.tick(time.delta_seconds()).just_finished() {
             info!("Entity timer just finished")
         }
     }
@@ -48,14 +48,14 @@ fn timer_system(time: Res<Time>, mut query: Query<&mut Timer>) {
 /// This system controls ticking the timer within the countdown resource and
 /// handling its state.
 fn countdown_system(time: Res<Time>, mut countdown: ResMut<Countdown>) {
-    countdown.main_timer.tick(time.delta_seconds);
+    countdown.main_timer.tick(time.delta_seconds());
 
     // The API encourages this kind of timer state checking (if you're only checking for one value)
     // Additionally, `finished()` would accomplish the same thing as `just_finished` due to the timer
     // being repeating, however this makes more sense visually.
     if countdown
         .percent_trigger
-        .tick(time.delta_seconds)
+        .tick(time.delta_seconds())
         .just_finished()
     {
         if !countdown.main_timer.finished() {
diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 6fb27c6e11fef..9b4795ba9ad24 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -174,7 +174,7 @@ fn paddle_movement_system(
 
         let translation = &mut transform.translation;
         // move the paddle horizontally
-        translation.x += time.delta_seconds * direction * paddle.speed;
+        translation.x += time.delta_seconds() * direction * paddle.speed;
         // bound the paddle within the walls
         translation.x = translation.x.min(380.0).max(-380.0);
     }
@@ -182,7 +182,7 @@ fn paddle_movement_system(
 
 fn ball_movement_system(time: Res<Time>, mut ball_query: Query<(&Ball, &mut Transform)>) {
     // clamp the timestep to stop the ball from escaping when the game starts
-    let delta_seconds = f32::min(0.2, time.delta_seconds);
+    let delta_seconds = f32::min(0.2, time.delta_seconds());
 
     for (ball, mut transform) in ball_query.iter_mut() {
         transform.translation += ball.velocity * delta_seconds;
diff --git a/examples/tools/bevymark.rs b/examples/tools/bevymark.rs
index da9dab64b8938..8685286a5a6b7 100644
--- a/examples/tools/bevymark.rs
+++ b/examples/tools/bevymark.rs
@@ -84,7 +84,7 @@ fn mouse_handler(
     mut counter: ResMut<BevyCounter>,
 ) {
     if mouse_button_input.pressed(MouseButton::Left) {
-        let spawn_count = (BIRDS_PER_SECOND as f32 * time.delta_seconds) as u128;
+        let spawn_count = (BIRDS_PER_SECOND as f32 * time.delta_seconds()) as u128;
         let bird_x = (window.width as i32 / -2) as f32 + HALF_BIRD_SIZE;
         let bird_y = (window.height / 2) as f32 - HALF_BIRD_SIZE;
 
@@ -118,9 +118,9 @@ fn mouse_handler(
 
 fn movement_system(time: Res<Time>, mut bird_query: Query<(&mut Bird, &mut Transform)>) {
     for (mut bird, mut transform) in bird_query.iter_mut() {
-        transform.translation.x += bird.velocity.x * time.delta_seconds;
-        transform.translation.y += bird.velocity.y * time.delta_seconds;
-        bird.velocity.y += GRAVITY * time.delta_seconds;
+        transform.translation.x += bird.velocity.x * time.delta_seconds();
+        transform.translation.y += bird.velocity.y * time.delta_seconds();
+        bird.velocity.y += GRAVITY * time.delta_seconds();
     }
 }
 
diff --git a/examples/ui/font_atlas_debug.rs b/examples/ui/font_atlas_debug.rs
index d5694d1bcb129..3b8b6edf055cc 100644
--- a/examples/ui/font_atlas_debug.rs
+++ b/examples/ui/font_atlas_debug.rs
@@ -62,7 +62,7 @@ fn atlas_render_system(
 }
 
 fn text_update_system(mut state: ResMut<State>, time: Res<Time>, mut query: Query<&mut Text>) {
-    if state.timer.tick(time.delta_seconds).finished() {
+    if state.timer.tick(time.delta_seconds()).finished() {
         for mut text in query.iter_mut() {
             let c = rand::random::<u8>() as char;
             if !text.value.contains(c) {
diff --git a/examples/wasm/winit_wasm.rs b/examples/wasm/winit_wasm.rs
index cc63adc23438e..c2c3ce8cd0086 100644
--- a/examples/wasm/winit_wasm.rs
+++ b/examples/wasm/winit_wasm.rs
@@ -34,7 +34,7 @@ fn counter(mut state: Local<CounterState>, time: Res<Time>) {
             "tick {} @ {:?} [Δ{}]",
             state.count,
             time.time_since_startup(),
-            time.delta_seconds
+            time.delta_seconds()
         );
     }
     state.count += 1;
diff --git a/examples/window/window_settings.rs b/examples/window/window_settings.rs
index 5e35f0df2d811..17fefd6f7b52f 100644
--- a/examples/window/window_settings.rs
+++ b/examples/window/window_settings.rs
@@ -22,7 +22,7 @@ fn change_title(time: Res<Time>, mut windows: ResMut<Windows>) {
     let window = windows.get_primary_mut().unwrap();
     window.set_title(format!(
         "Seconds since startup: {}",
-        time.seconds_since_startup.round()
+        time.seconds_since_startup().round()
     ));
 }