custom_schedule/
custom_schedule.rs

1//! Demonstrates how to add custom schedules that run in Bevy's `Main` schedule, ordered relative to Bevy's built-in
2//! schedules such as `Update` or `Last`.
3
4use bevy::{
5    app::MainScheduleOrder,
6    ecs::schedule::{ExecutorKind, ScheduleLabel},
7    prelude::*,
8};
9
10#[derive(ScheduleLabel, Debug, Hash, PartialEq, Eq, Clone)]
11struct SingleThreadedUpdate;
12
13#[derive(ScheduleLabel, Debug, Hash, PartialEq, Eq, Clone)]
14struct CustomStartup;
15
16fn main() {
17    let mut app = App::new();
18
19    // Create a new [`Schedule`]. For demonstration purposes, we configure it to use a single threaded executor so that
20    // systems in this schedule are never run in parallel. However, this is not a requirement for custom schedules in
21    // general.
22    let mut custom_update_schedule = Schedule::new(SingleThreadedUpdate);
23    custom_update_schedule.set_executor_kind(ExecutorKind::SingleThreaded);
24
25    // Adding the schedule to the app does not automatically run the schedule. This merely registers the schedule so
26    // that systems can look it up using the `Schedules` resource.
27    app.add_schedule(custom_update_schedule);
28
29    // Bevy `App`s have a `main_schedule_label` field that configures which schedule is run by the App's `runner`.
30    // By default, this is `Main`. The `Main` schedule is responsible for running Bevy's main schedules such as
31    // `Update`, `Startup` or `Last`.
32    //
33    // We can configure the `Main` schedule to run our custom update schedule relative to the existing ones by modifying
34    // the `MainScheduleOrder` resource.
35    //
36    // Note that we modify `MainScheduleOrder` directly in `main` and not in a startup system. The reason for this is
37    // that the `MainScheduleOrder` cannot be modified from systems that are run as part of the `Main` schedule.
38    let mut main_schedule_order = app.world_mut().resource_mut::<MainScheduleOrder>();
39    main_schedule_order.insert_after(Update, SingleThreadedUpdate);
40
41    // Adding a custom startup schedule works similarly, but needs to use `insert_startup_after`
42    // instead of `insert_after`.
43    app.add_schedule(Schedule::new(CustomStartup));
44
45    let mut main_schedule_order = app.world_mut().resource_mut::<MainScheduleOrder>();
46    main_schedule_order.insert_startup_after(PreStartup, CustomStartup);
47
48    app.add_systems(SingleThreadedUpdate, single_threaded_update_system)
49        .add_systems(CustomStartup, custom_startup_system)
50        .add_systems(PreStartup, pre_startup_system)
51        .add_systems(Startup, startup_system)
52        .add_systems(First, first_system)
53        .add_systems(Update, update_system)
54        .add_systems(Last, last_system)
55        .run();
56}
57
58fn pre_startup_system() {
59    println!("Pre Startup");
60}
61
62fn startup_system() {
63    println!("Startup");
64}
65
66fn custom_startup_system() {
67    println!("Custom Startup");
68}
69
70fn first_system() {
71    println!("First");
72}
73
74fn update_system() {
75    println!("Update");
76}
77
78fn single_threaded_update_system() {
79    println!("Single Threaded Update");
80}
81
82fn last_system() {
83    println!("Last");
84}
custom_schedule/custom_schedule.rs

custom_schedule/
custom_schedule.rs
