From 9a3d5b4a98fef6366af5251e375f18e5ea569645 Mon Sep 17 00:00:00 2001
From: Mike Hsu <mike.hsu@gmail.com>
Date: Mon, 1 Mar 2021 21:55:11 -0800
Subject: [PATCH 1/4] change to a fixed timestep

---
 examples/game/breakout.rs | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 23169838dc33b..6c3882334e7c2 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -1,23 +1,35 @@
 use bevy::{
+    core::{FixedTimestep},
     prelude::*,
     render::pass::ClearColor,
     sprite::collide_aabb::{collide, Collision},
 };
 
 /// An implementation of the classic game "Breakout"
+const TIME_STEP: f32 = 1.0 / 60.0;
 fn main() {
     App::build()
         .add_plugins(DefaultPlugins)
         .insert_resource(Scoreboard { score: 0 })
         .insert_resource(ClearColor(Color::rgb(0.9, 0.9, 0.9)))
         .add_startup_system(setup.system())
-        .add_system(paddle_movement_system.system())
-        .add_system(ball_collision_system.system())
-        .add_system(ball_movement_system.system())
+        .add_stage(
+            FixedUpdateStage,
+            SystemStage::parallel()
+                .with_run_criteria(
+                    FixedTimestep::step(TIME_STEP as f64)
+                )
+                .with_system(paddle_movement_system.system())
+                .with_system(ball_collision_system.system())
+                .with_system(ball_movement_system.system()),
+        )
         .add_system(scoreboard_system.system())
         .run();
 }
 
+#[derive(Debug, Hash, PartialEq, Eq, Clone, StageLabel)]
+struct FixedUpdateStage;
+
 struct Paddle {
     speed: f32,
 }
@@ -175,7 +187,6 @@ fn setup(
 }
 
 fn paddle_movement_system(
-    time: Res<Time>,
     keyboard_input: Res<Input<KeyCode>>,
     mut query: Query<(&Paddle, &mut Transform)>,
 ) {
@@ -191,18 +202,15 @@ fn paddle_movement_system(
 
         let translation = &mut transform.translation;
         // move the paddle horizontally
-        translation.x += time.delta_seconds() * direction * paddle.speed;
+        translation.x += direction * paddle.speed;
         // bound the paddle within the walls
         translation.x = translation.x.min(380.0).max(-380.0);
     }
 }
 
-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());
-
+fn ball_movement_system(mut ball_query: Query<(&Ball, &mut Transform)>) {
     if let Ok((ball, mut transform)) = ball_query.single_mut() {
-        transform.translation += ball.velocity * delta_seconds;
+        transform.translation += ball.velocity;
     }
 }
 

From fc32a4d549a3c14e3dd7c662cb16446077198736 Mon Sep 17 00:00:00 2001
From: Mike Hsu <mike.hsu@gmail.com>
Date: Mon, 15 Mar 2021 16:42:18 -0700
Subject: [PATCH 2/4] make physics systems dependent on TIME_STEP

---
 examples/game/breakout.rs | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 6c3882334e7c2..08cfccb44800d 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -16,9 +16,7 @@ fn main() {
         .add_stage(
             FixedUpdateStage,
             SystemStage::parallel()
-                .with_run_criteria(
-                    FixedTimestep::step(TIME_STEP as f64)
-                )
+                .with_run_criteria(FixedTimestep::step(TIME_STEP as f64))
                 .with_system(paddle_movement_system.system())
                 .with_system(ball_collision_system.system())
                 .with_system(ball_movement_system.system()),
@@ -202,7 +200,7 @@ fn paddle_movement_system(
 
         let translation = &mut transform.translation;
         // move the paddle horizontally
-        translation.x += direction * paddle.speed;
+        translation.x += direction * paddle.speed * TIME_STEP;
         // bound the paddle within the walls
         translation.x = translation.x.min(380.0).max(-380.0);
     }
@@ -210,7 +208,7 @@ fn paddle_movement_system(
 
 fn ball_movement_system(mut ball_query: Query<(&Ball, &mut Transform)>) {
     if let Ok((ball, mut transform)) = ball_query.single_mut() {
-        transform.translation += ball.velocity;
+        transform.translation += ball.velocity * TIME_STEP;
     }
 }
 

From 19a1863c213cb12a9bf21a9f99c3d2bb22678781 Mon Sep 17 00:00:00 2001
From: Mike Hsu <mike.hsu@gmail.com>
Date: Mon, 5 Apr 2021 10:33:58 -0700
Subject: [PATCH 3/4] run cargo fmt

---
 examples/game/breakout.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 08cfccb44800d..2dd3d0cf45ce5 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -1,5 +1,5 @@
 use bevy::{
-    core::{FixedTimestep},
+    core::FixedTimestep,
     prelude::*,
     render::pass::ClearColor,
     sprite::collide_aabb::{collide, Collision},

From e612600ffcfc198f5229ecfa05be532305253a35 Mon Sep 17 00:00:00 2001
From: Carter Anderson <mcanders1@gmail.com>
Date: Mon, 12 Apr 2021 12:24:54 -0700
Subject: [PATCH 4/4] use system set instead of stage

---
 examples/game/breakout.rs | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 2dd3d0cf45ce5..5fc2ccf143efa 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -13,9 +13,8 @@ fn main() {
         .insert_resource(Scoreboard { score: 0 })
         .insert_resource(ClearColor(Color::rgb(0.9, 0.9, 0.9)))
         .add_startup_system(setup.system())
-        .add_stage(
-            FixedUpdateStage,
-            SystemStage::parallel()
+        .add_system_set(
+            SystemSet::new()
                 .with_run_criteria(FixedTimestep::step(TIME_STEP as f64))
                 .with_system(paddle_movement_system.system())
                 .with_system(ball_collision_system.system())
@@ -25,9 +24,6 @@ fn main() {
         .run();
 }
 
-#[derive(Debug, Hash, PartialEq, Eq, Clone, StageLabel)]
-struct FixedUpdateStage;
-
 struct Paddle {
     speed: f32,
 }