Add new example to explore time

Cargo.toml

@@ -1231,6 +1231,16 @@ description = "Illustrates creating custom system parameters with `SystemParam`"
 category = "ECS (Entity Component System)"
 wasm = false
 
+[[example]]
+name = "time"
+path = "examples/ecs/time.rs"
+
+[package.metadata.example.time]
+name = "Time handling"
+description = "Explains how Time is handled in ECS"
+category = "ECS (Entity Component System)"
+wasm = false
+
 [[example]]
 name = "timers"
 path = "examples/ecs/timers.rs"

examples/README.md

@@ -227,6 +227,7 @@ Example | Description
 [System Closure](../examples/ecs/system_closure.rs) | Show how to use closures as systems, and how to configure `Local` variables by capturing external state
 [System Parameter](../examples/ecs/system_param.rs) | Illustrates creating custom system parameters with `SystemParam`
 [System Piping](../examples/ecs/system_piping.rs) | Pipe the output of one system into a second, allowing you to handle any errors gracefully
+[Time handling](../examples/ecs/time.rs) | Explains how Time is handled in ECS
 [Timers](../examples/ecs/timers.rs) | Illustrates ticking `Timer` resources inside systems and handling their state
 
 ## Games

examples/ecs/time.rs

@@ -0,0 +1,115 @@
+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!(" n: 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();
+}