docs/bevy/examples/time/time.rs 3.6 K · 121 lines · raw · history

1 //! An example that illustrates how Time is handled in ECS.
2
3 use bevy::{app::AppExit, prelude::*};
4
5 use std::{
6 io::{self, BufRead},
7 time::Duration,
8 };
9
10 fn banner() {
11 println!("This example is meant to intuitively demonstrate how Time works in Bevy.");
12 println!();
13 println!("Time will be printed in three different schedules in the app:");
14 println!("- PreUpdate: real time is printed");
15 println!("- FixedUpdate: fixed time step time is printed, may be run zero or multiple times");
16 println!("- Update: virtual game time is printed");
17 println!();
18 println!("Max delta time is set to 5 seconds. Fixed timestep is set to 1 second.");
19 println!();
20 }
21
22 fn help() {
23 println!("The app reads commands line-by-line from standard input.");
24 println!();
25 println!("Commands:");
26 println!(" empty line: Run app.update() once on the Bevy App");
27 println!(" q: Quit the app.");
28 println!(" f: Set speed to fast, 2x");
29 println!(" n: Set speed to normal, 1x");
30 println!(" s: Set speed to slow, 0.5x");
31 println!(" p: Pause");
32 println!(" u: Unpause");
33 }
34
35 fn runner(mut app: App) -> AppExit {
36 banner();
37 help();
38 let stdin = io::stdin();
39 for line in stdin.lock().lines() {
40 if let Err(err) = line {
41 println!("read err: {err:#}");
42 break;
43 }
44 match line.unwrap().as_str() {
45 "" => {
46 app.update();
47 }
48 "f" => {
49 println!("FAST: setting relative speed to 2x");
50 app.world_mut()
51 .resource_mut::<Time<Virtual>>()
52 .set_relative_speed(2.0);
53 }
54 "n" => {
55 println!("NORMAL: setting relative speed to 1x");
56 app.world_mut()
57 .resource_mut::<Time<Virtual>>()
58 .set_relative_speed(1.0);
59 }
60 "s" => {
61 println!("SLOW: setting relative speed to 0.5x");
62 app.world_mut()
63 .resource_mut::<Time<Virtual>>()
64 .set_relative_speed(0.5);
65 }
66 "p" => {
67 println!("PAUSE: pausing virtual clock");
68 app.world_mut().resource_mut::<Time<Virtual>>().pause();
69 }
70 "u" => {
71 println!("UNPAUSE: resuming virtual clock");
72 app.world_mut().resource_mut::<Time<Virtual>>().unpause();
73 }
74 "q" => {
75 println!("QUITTING!");
76 break;
77 }
78 _ => {
79 help();
80 }
81 }
82 }
83
84 AppExit::Success
85 }
86
87 fn print_real_time(time: Res<Time<Real>>) {
88 println!(
89 "PreUpdate: this is real time clock, delta is {:?} and elapsed is {:?}",
90 time.delta(),
91 time.elapsed()
92 );
93 }
94
95 fn print_fixed_time(time: Res<Time>) {
96 println!(
97 "FixedUpdate: this is generic time clock inside fixed, delta is {:?} and elapsed is {:?}",
98 time.delta(),
99 time.elapsed()
100 );
101 }
102
103 fn print_time(time: Res<Time>) {
104 println!(
105 "Update: this is generic time clock, delta is {:?} and elapsed is {:?}",
106 time.delta(),
107 time.elapsed()
108 );
109 }
110
111 fn main() {
112 App::new()
113 .add_plugins(MinimalPlugins)
114 .insert_resource(Time::<Virtual>::from_max_delta(Duration::from_secs(5)))
115 .insert_resource(Time::<Fixed>::from_duration(Duration::from_secs(1)))
116 .add_systems(PreUpdate, print_real_time)
117 .add_systems(FixedUpdate, print_fixed_time)
118 .add_systems(Update, print_time)
119 .set_runner(runner)
120 .run();
121 }