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logs.rs
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logs.rs
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//! This example illustrates how to use logs in bevy.
use bevy::{log::once, prelude::*};
fn main() {
App::new()
.add_plugins(DefaultPlugins.set(bevy::log::LogPlugin {
// Uncomment this to override the default log settings:
// level: bevy::log::Level::TRACE,
// filter: "wgpu=warn,bevy_ecs=info".to_string(),
..default()
}))
.add_systems(Startup, setup)
.add_systems(Update, log_system)
.add_systems(Update, log_once_system)
.add_systems(Update, panic_on_p)
.run();
}
fn setup(mut commands: Commands) {
commands.spawn(Camera2d);
commands.spawn((
Text::new("Press P to panic"),
Node {
position_type: PositionType::Absolute,
top: Val::Px(12.0),
left: Val::Px(12.0),
..default()
},
));
}
fn panic_on_p(keys: Res<ButtonInput<KeyCode>>) {
if keys.just_pressed(KeyCode::KeyP) {
panic!("P pressed, panicking");
}
}
fn log_system() {
// here is how you write new logs at each "log level" (in "least important" to "most important"
// order)
trace!("very noisy");
debug!("helpful for debugging");
info!("helpful information that is worth printing by default");
warn!("something bad happened that isn't a failure, but thats worth calling out");
error!("something failed");
// by default, trace and debug logs are ignored because they are "noisy"
// you can control what level is logged by setting up the LogPlugin
// alternatively you can set the log level via the RUST_LOG=LEVEL environment variable
// ex: RUST_LOG=trace, RUST_LOG=info,bevy_ecs=warn
// the format used here is super flexible. check out this documentation for more info:
// https://docs.rs/tracing-subscriber/*/tracing_subscriber/filter/struct.EnvFilter.html
}
fn log_once_system() {
// The 'once' variants of each log level are useful when a system is called every frame,
// but we still wish to inform the user only once. In other words, use these to prevent spam :)
trace_once!("one time noisy message");
debug_once!("one time debug message");
info_once!("some info which is printed only once");
warn_once!("some warning we wish to call out only once");
error_once!("some error we wish to report only once");
for i in 0..10 {
info_once!("logs once per call site, so this works just fine: {}", i);
}
// you can also use the `once!` macro directly,
// in situations where you want to do something expensive only once
// within the context of a continuous system.
once!({
info!("doing expensive things");
let mut a: u64 = 0;
for i in 0..100000000 {
a += i;
}
info!("result of some expensive one time calculation: {}", a);
});
}