change breakout to use FixedTime::period (#8076)

examples/games/breakout.rs

@@ -6,9 +6,6 @@ use bevy::{
     sprite::MaterialMesh2dBundle,
 };
 
-// Defines the amount of time that should elapse between each physics step.
-const TIME_STEP: f32 = 1.0 / 60.0;
-
 // These constants are defined in `Transform` units.
 // Using the default 2D camera they correspond 1:1 with screen pixels.
 const PADDLE_SIZE: Vec3 = Vec3::new(120.0, 20.0, 0.0);
@@ -70,7 +67,7 @@ fn main() {
                 .in_schedule(CoreSchedule::FixedUpdate),
         )
         // Configure how frequently our gameplay systems are run
-        .insert_resource(FixedTime::new_from_secs(TIME_STEP))
+        .insert_resource(FixedTime::new_from_secs(1.0 / 60.0))
         .add_system(update_scoreboard)
         .add_system(bevy::window::close_on_esc)
         .run();
@@ -315,6 +312,7 @@ fn setup(
 fn move_paddle(
     keyboard_input: Res<Input<KeyCode>>,
     mut query: Query<&mut Transform, With<Paddle>>,
+    time_step: Res<FixedTime>,
 ) {
     let mut paddle_transform = query.single_mut();
     let mut direction = 0.0;
@@ -328,7 +326,8 @@ fn move_paddle(
     }
 
     // Calculate the new horizontal paddle position based on player input
-    let new_paddle_position = paddle_transform.translation.x + direction * PADDLE_SPEED * TIME_STEP;
+    let new_paddle_position =
+        paddle_transform.translation.x + direction * PADDLE_SPEED * time_step.period.as_secs_f32();
 
     // Update the paddle position,
     // making sure it doesn't cause the paddle to leave the arena
@@ -338,10 +337,10 @@ fn move_paddle(
     paddle_transform.translation.x = new_paddle_position.clamp(left_bound, right_bound);
 }
 
-fn apply_velocity(mut query: Query<(&mut Transform, &Velocity)>) {
+fn apply_velocity(mut query: Query<(&mut Transform, &Velocity)>, time_step: Res<FixedTime>) {
     for (mut transform, velocity) in &mut query {
-        transform.translation.x += velocity.x * TIME_STEP;
-        transform.translation.y += velocity.y * TIME_STEP;
+        transform.translation.x += velocity.x * time_step.period.as_secs_f32();
+        transform.translation.y += velocity.y * time_step.period.as_secs_f32();
     }
 }