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time.rs
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time.rs
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//! An example that illustrates how Time is handled in ECS.
use bevy::prelude::*;
use std::io::{self, BufRead};
use std::time::Duration;
fn banner() {
println!("This example is meant to intuitively demonstrate how Time works in Bevy.");
println!();
println!("Time will be printed in three different schedules in the app:");
println!("- PreUpdate: real time is printed");
println!("- FixedUpdate: fixed time step time is printed, may be run zero or multiple times");
println!("- Update: virtual game time is printed");
println!();
println!("Max delta time is set to 5 seconds. Fixed timestep is set to 1 second.");
println!();
}
fn help() {
println!("The app reads commands line-by-line from standard input.");
println!();
println!("Commands:");
println!(" empty line: Run app.update() once on the Bevy App");
println!(" q: Quit the app.");
println!(" f: Set speed to fast, 2x");
println!(" n: Set speed to normal, 1x");
println!(" s: Set speed to slow, 0.5x");
println!(" p: Pause");
println!(" u: Unpause");
}
fn runner(mut app: App) {
banner();
help();
let stdin = io::stdin();
for line in stdin.lock().lines() {
if let Err(err) = line {
println!("read err: {:#}", err);
break;
}
match line.unwrap().as_str() {
"" => {
app.update();
}
"f" => {
println!("FAST: setting relative speed to 2x");
app.world
.resource_mut::<Time<Virtual>>()
.set_relative_speed(2.0);
}
"n" => {
println!("NORMAL: setting relative speed to 1x");
app.world
.resource_mut::<Time<Virtual>>()
.set_relative_speed(1.0);
}
"s" => {
println!("SLOW: setting relative speed to 0.5x");
app.world
.resource_mut::<Time<Virtual>>()
.set_relative_speed(0.5);
}
"p" => {
println!("PAUSE: pausing virtual clock");
app.world.resource_mut::<Time<Virtual>>().pause();
}
"u" => {
println!("UNPAUSE: resuming virtual clock");
app.world.resource_mut::<Time<Virtual>>().unpause();
}
"q" => {
println!("QUITTING!");
break;
}
_ => {
help();
}
}
}
}
fn print_real_time(time: Res<Time<Real>>) {
println!(
"PreUpdate: this is real time clock, delta is {:?} and elapsed is {:?}",
time.delta(),
time.elapsed()
);
}
fn print_fixed_time(time: Res<Time>) {
println!(
"FixedUpdate: this is generic time clock inside fixed, delta is {:?} and elapsed is {:?}",
time.delta(),
time.elapsed()
);
}
fn print_time(time: Res<Time>) {
println!(
"Update: this is generic time clock, delta is {:?} and elapsed is {:?}",
time.delta(),
time.elapsed()
);
}
fn main() {
App::new()
.add_plugins(MinimalPlugins)
.insert_resource(Time::<Virtual>::from_max_delta(Duration::from_secs(5)))
.insert_resource(Time::<Fixed>::from_duration(Duration::from_secs(1)))
.add_systems(PreUpdate, print_real_time)
.add_systems(FixedUpdate, print_fixed_time)
.add_systems(Update, print_time)
.set_runner(runner)
.run();
}