Schedule V2

Cargo.toml

@@ -193,10 +193,18 @@ path = "examples/diagnostics/print_diagnostics.rs"
 name = "event"
 path = "examples/ecs/event.rs"
 
+[[example]]
+name = "fixed_timestep"
+path = "examples/ecs/fixed_timestep.rs"
+
 [[example]]
 name = "startup_system"
 path = "examples/ecs/startup_system.rs"
 
+[[example]]
+name = "state"
+path = "examples/ecs/state.rs"
+
 [[example]]
 name = "system_chaining"
 path = "examples/ecs/system_chaining.rs"

crates/bevy_app/src/app.rs

@@ -1,5 +1,5 @@
 use crate::app_builder::AppBuilder;
-use bevy_ecs::{ParallelExecutor, Resources, Schedule, World};
+use bevy_ecs::{Resources, Schedule, Stage, World};
 #[cfg(feature = "trace")]
 use bevy_utils::tracing::info_span;
 
@@ -30,9 +30,6 @@ pub struct App {
     pub resources: Resources,
     pub runner: Box<dyn Fn(App)>,
     pub schedule: Schedule,
-    pub executor: ParallelExecutor,
-    pub startup_schedule: Schedule,
-    pub startup_executor: ParallelExecutor,
 }
 
 impl Default for App {
@@ -41,16 +38,12 @@ impl Default for App {
             world: Default::default(),
             resources: Default::default(),
             schedule: Default::default(),
-            executor: Default::default(),
-            startup_schedule: Default::default(),
-            startup_executor: ParallelExecutor::without_tracker_clears(),
             runner: Box::new(run_once),
         }
     }
 }
 
 fn run_once(mut app: App) {
-    app.initialize();
     app.update();
 }
 
@@ -60,35 +53,15 @@ impl App {
     }
 
     pub fn update(&mut self) {
-        self.schedule
-            .initialize(&mut self.world, &mut self.resources);
-        self.executor
-            .run(&mut self.schedule, &mut self.world, &mut self.resources);
-    }
-
-    pub fn initialize(&mut self) {
-        #[cfg(feature = "trace")]
-        let startup_schedule_span = info_span!("startup_schedule");
-        #[cfg(feature = "trace")]
-        let _startup_schedule_guard = startup_schedule_span.enter();
-        self.startup_schedule
-            .initialize(&mut self.world, &mut self.resources);
-        self.startup_executor.initialize(&mut self.resources);
-        self.startup_executor.run(
-            &mut self.startup_schedule,
-            &mut self.world,
-            &mut self.resources,
-        );
+        self.schedule.run(&mut self.world, &mut self.resources);
     }
 
     pub fn run(mut self) {
         #[cfg(feature = "trace")]
-        let bevy_app_run_span = info_span!("bevy_app_run");
+        let bevy_app_run_span = info_span!("bevy_app");
         #[cfg(feature = "trace")]
         let _bevy_app_run_guard = bevy_app_run_span.enter();
 
-        self.executor.initialize(&mut self.resources);
-
         let runner = std::mem::replace(&mut self.runner, Box::new(run_once));
         (runner)(self);
     }

crates/bevy_app/src/app_builder.rs

@@ -1,10 +1,15 @@
+use std::any::Any;
+
 use crate::{
     app::{App, AppExit},
     event::Events,
     plugin::Plugin,
     stage, startup_stage, PluginGroup, PluginGroupBuilder,
 };
-use bevy_ecs::{FromResources, IntoSystem, Resources, System, World};
+use bevy_ecs::{
+    clear_trackers_system, FromResources, IntoStage, IntoSystem, Resource, Resources, RunOnce,
+    Schedule, Stage, State, StateStage, System, SystemStage, World,
+};
 use bevy_utils::tracing::debug;
 
 /// Configure [App]s using the builder pattern
@@ -18,8 +23,10 @@ impl Default for AppBuilder {
             app: App::default(),
         };
 
-        app_builder.add_default_stages();
-        app_builder.add_event::<AppExit>();
+        app_builder
+            .add_default_stages()
+            .add_event::<AppExit>()
+            .add_system_to_stage(stage::LAST, clear_trackers_system);
         app_builder
     }
 }
@@ -49,55 +56,88 @@ impl AppBuilder {
         self
     }
 
-    pub fn add_stage(&mut self, stage_name: &'static str) -> &mut Self {
-        self.app.schedule.add_stage(stage_name);
+    pub fn add_stage<Params, S: IntoStage<Params>>(
+        &mut self,
+        name: &'static str,
+        stage: S,
+    ) -> &mut Self {
+        self.app.schedule.add_stage(name, stage);
         self
     }
 
-    pub fn add_stage_after(&mut self, target: &'static str, stage_name: &'static str) -> &mut Self {
-        self.app.schedule.add_stage_after(target, stage_name);
+    pub fn add_stage_after<Params, S: IntoStage<Params>>(
+        &mut self,
+        target: &'static str,
+        name: &'static str,
+        stage: S,
+    ) -> &mut Self {
+        self.app.schedule.add_stage_after(target, name, stage);
         self
     }
 
-    pub fn add_stage_before(
+    pub fn add_stage_before<Params, S: IntoStage<Params>>(
         &mut self,
         target: &'static str,
-        stage_name: &'static str,
+        name: &'static str,
+        stage: S,
     ) -> &mut Self {
-        self.app.schedule.add_stage_before(target, stage_name);
+        self.app.schedule.add_stage_before(target, name, stage);
         self
     }
 
-    pub fn add_startup_stage(&mut self, stage_name: &'static str) -> &mut Self {
-        self.app.startup_schedule.add_stage(stage_name);
+    pub fn add_startup_stage<Params, S: IntoStage<Params>>(
+        &mut self,
+        name: &'static str,
+        stage: S,
+    ) -> &mut Self {
+        self.app
+            .schedule
+            .stage(stage::STARTUP, |schedule: &mut Schedule| {
+                schedule.add_stage(name, stage)
+            });
         self
     }
 
-    pub fn add_startup_stage_after(
+    pub fn add_startup_stage_after<Params, S: IntoStage<Params>>(
         &mut self,
         target: &'static str,
-        stage_name: &'static str,
+        name: &'static str,
+        stage: S,
     ) -> &mut Self {
         self.app
-            .startup_schedule
-            .add_stage_after(target, stage_name);
+            .schedule
+            .stage(stage::STARTUP, |schedule: &mut Schedule| {
+                schedule.add_stage_after(target, name, stage)
+            });
         self
     }
 
-    pub fn add_startup_stage_before(
+    pub fn add_startup_stage_before<Params, S: IntoStage<Params>>(
         &mut self,
         target: &'static str,
-        stage_name: &'static str,
+        name: &'static str,
+        stage: S,
     ) -> &mut Self {
         self.app
-            .startup_schedule
-            .add_stage_before(target, stage_name);
+            .schedule
+            .stage(stage::STARTUP, |schedule: &mut Schedule| {
+                schedule.add_stage_before(target, name, stage)
+            });
+        self
+    }
+
+    pub fn stage<T: Stage, F: FnOnce(&mut T) -> &mut T>(
+        &mut self,
+        name: &str,
+        func: F,
+    ) -> &mut Self {
+        self.app.schedule.stage(name, func);
         self
     }
 
     pub fn add_system<S, Params, IntoS>(&mut self, system: IntoS) -> &mut Self
     where
-        S: System<Input = (), Output = ()>,
+        S: System<In = (), Out = ()>,
         IntoS: IntoSystem<Params, S>,
     {
         self.add_system_to_stage(stage::UPDATE, system)
@@ -109,37 +149,41 @@ impl AppBuilder {
         system: IntoS,
     ) -> &mut Self
     where
-        S: System<Input = (), Output = ()>,
+        S: System<In = (), Out = ()>,
         IntoS: IntoSystem<Params, S>,
     {
         self.app
-            .startup_schedule
-            .add_system_to_stage(stage_name, system);
+            .schedule
+            .stage(stage::STARTUP, |schedule: &mut Schedule| {
+                schedule.add_system_to_stage(stage_name, system)
+            });
         self
     }
 
     pub fn add_startup_system<S, Params, IntoS>(&mut self, system: IntoS) -> &mut Self
     where
-        S: System<Input = (), Output = ()>,
+        S: System<In = (), Out = ()>,
         IntoS: IntoSystem<Params, S>,
     {
-        self.app
-            .startup_schedule
-            .add_system_to_stage(startup_stage::STARTUP, system);
-        self
+        self.add_startup_system_to_stage(startup_stage::STARTUP, system)
     }
 
     pub fn add_default_stages(&mut self) -> &mut Self {
-        self.add_startup_stage(startup_stage::PRE_STARTUP)
-            .add_startup_stage(startup_stage::STARTUP)
-            .add_startup_stage(startup_stage::POST_STARTUP)
-            .add_stage(stage::FIRST)
-            .add_stage(stage::PRE_EVENT)
-            .add_stage(stage::EVENT)
-            .add_stage(stage::PRE_UPDATE)
-            .add_stage(stage::UPDATE)
-            .add_stage(stage::POST_UPDATE)
-            .add_stage(stage::LAST)
+        self.add_stage(
+            stage::STARTUP,
+            Schedule::default()
+                .with_run_criteria(RunOnce::default())
+                .with_stage(startup_stage::PRE_STARTUP, SystemStage::parallel())
+                .with_stage(startup_stage::STARTUP, SystemStage::parallel())
+                .with_stage(startup_stage::POST_STARTUP, SystemStage::parallel()),
+        )
+        .add_stage(stage::FIRST, SystemStage::parallel())
+        .add_stage(stage::PRE_EVENT, SystemStage::parallel())
+        .add_stage(stage::EVENT, SystemStage::parallel())
+        .add_stage(stage::PRE_UPDATE, SystemStage::parallel())
+        .add_stage(stage::UPDATE, SystemStage::parallel())
+        .add_stage(stage::POST_UPDATE, SystemStage::parallel())
+        .add_stage(stage::LAST, SystemStage::parallel())
     }
 
     pub fn add_system_to_stage<S, Params, IntoS>(
@@ -148,28 +192,13 @@ impl AppBuilder {
         system: IntoS,
     ) -> &mut Self
     where
-        S: System<Input = (), Output = ()>,
+        S: System<In = (), Out = ()>,
         IntoS: IntoSystem<Params, S>,
     {
         self.app.schedule.add_system_to_stage(stage_name, system);
         self
     }
 
-    pub fn add_system_to_stage_front<S, Params, IntoS>(
-        &mut self,
-        stage_name: &'static str,
-        system: IntoS,
-    ) -> &mut Self
-    where
-        S: System<Input = (), Output = ()>,
-        IntoS: IntoSystem<Params, S>,
-    {
-        self.app
-            .schedule
-            .add_system_to_stage_front(stage_name, system.system());
-        self
-    }
-
     pub fn add_event<T>(&mut self) -> &mut Self
     where
         T: Send + Sync + 'static,
@@ -178,6 +207,53 @@ impl AppBuilder {
             .add_system_to_stage(stage::EVENT, Events::<T>::update_system)
     }
 
+    pub fn state_stage_name<T: Any>() -> String {
+        format!("state({})", std::any::type_name::<T>())
+    }
+
+    pub fn add_state<T: Clone + Resource>(&mut self, initial: T) -> &mut Self {
+        self.add_resource(State::new(initial));
+        self.app.schedule.add_stage_after(
+            stage::UPDATE,
+            &Self::state_stage_name::<T>(),
+            StateStage::<T>::default(),
+        );
+        self
+    }
+
+    pub fn on_state_enter<T: Clone + Resource, Params, S: IntoStage<Params>>(
+        &mut self,
+        value: T,
+        stage: S,
+    ) -> &mut Self {
+        self.stage(
+            &Self::state_stage_name::<T>(),
+            |state_stage: &mut StateStage<T>| state_stage.on_state_enter(value, stage),
+        )
+    }
+
+    pub fn on_state_update<T: Clone + Resource, Params, S: IntoStage<Params>>(
+        &mut self,
+        value: T,
+        stage: S,
+    ) -> &mut Self {
+        self.stage(
+            &Self::state_stage_name::<T>(),
+            |state_stage: &mut StateStage<T>| state_stage.on_state_update(value, stage),
+        )
+    }
+
+    pub fn on_state_exit<T: Clone + Resource, Params, S: IntoStage<Params>>(
+        &mut self,
+        value: T,
+        stage: S,
+    ) -> &mut Self {
+        self.stage(
+            &Self::state_stage_name::<T>(),
+            |state_stage: &mut StateStage<T>| state_stage.on_state_exit(value, stage),
+        )
+    }
+
     /// Adds a resource to the current [App] and overwrites any resource previously added of the same type.
     pub fn add_resource<T>(&mut self, resource: T) -> &mut Self
     where

crates/bevy_app/src/schedule_runner.rs

@@ -56,8 +56,6 @@ impl Plugin for ScheduleRunnerPlugin {
             .get_or_insert_with(ScheduleRunnerSettings::default)
             .to_owned();
         app.set_runner(move |mut app: App| {
-            app.initialize();
-
             let mut app_exit_event_reader = EventReader::<AppExit>::default();
             match settings.run_mode {
                 RunMode::Once => {

crates/bevy_app/src/stage.rs

@@ -1,11 +1,14 @@
+/// Name of the app stage that runs once at the beginning of the app
+pub const STARTUP: &str = "startup";
+
 /// Name of app stage that runs before all other app stages
 pub const FIRST: &str = "first";
 
 /// Name of app stage that runs before EVENT
-pub const PRE_EVENT: &str = "pre_events";
+pub const PRE_EVENT: &str = "pre_event";
 
 /// Name of app stage that updates events. Runs before UPDATE
-pub const EVENT: &str = "events";
+pub const EVENT: &str = "event";
 
 /// Name of app stage responsible for performing setup before an update. Runs before UPDATE.
 pub const PRE_UPDATE: &str = "pre_update";