93 lines
3.6 KiB
Rust
93 lines
3.6 KiB
Rust
use bevy_utils::tracing::warn;
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use crate::{
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archetype::{Archetype, ArchetypeComponentId},
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component::ComponentId,
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query::Access,
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world::World,
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};
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use std::borrow::Cow;
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/// A [`System`] identifier.
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#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
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pub struct SystemId(pub usize);
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impl SystemId {
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/// Creates a new random `SystemId`.
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#[allow(clippy::new_without_default)]
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pub fn new() -> Self {
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SystemId(rand::random::<usize>())
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}
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}
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/// An ECS system that can be added to a [Schedule](crate::schedule::Schedule)
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///
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/// Systems are functions with all arguments implementing [SystemParam](crate::system::SystemParam).
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///
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/// Systems are added to an application using `AppBuilder::add_system(my_system.system())`
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/// or similar methods, and will generally run once per pass of the main loop.
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///
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/// Systems are executed in parallel, in opportunistic order; data access is managed automatically.
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/// It's possible to specify explicit execution order between specific systems,
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/// see [SystemDescriptor](crate::schedule::SystemDescriptor).
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pub trait System: Send + Sync + 'static {
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/// The system's input. See [`In`](crate::system::In) for
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/// [`FunctionSystem`](crate::system::FunctionSystem)s.
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type In;
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/// The system's output.
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type Out;
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/// Returns the system's name.
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fn name(&self) -> Cow<'static, str>;
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/// Returns the system's [`SystemId`].
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fn id(&self) -> SystemId;
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/// Register a new archetype for this system.
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fn new_archetype(&mut self, archetype: &Archetype);
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/// Returns the system's component [`Access`].
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fn component_access(&self) -> &Access<ComponentId>;
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/// Returns the system's archetype component [`Access`].
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fn archetype_component_access(&self) -> &Access<ArchetypeComponentId>;
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/// Returns true if the system is [`Send`].
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fn is_send(&self) -> bool;
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/// Runs the system with the given input in the world. Unlike [`System::run`], this function
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/// takes a shared reference to [`World`] and may therefore break Rust's aliasing rules, making
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/// it unsafe to call.
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///
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/// # Safety
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///
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/// This might access world and resources in an unsafe manner. This should only be called in one
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/// of the following contexts:
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/// 1. This system is the only system running on the given world across all threads.
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/// 2. This system only runs in parallel with other systems that do not conflict with the
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/// [`System::archetype_component_access()`].
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unsafe fn run_unsafe(&mut self, input: Self::In, world: &World) -> Self::Out;
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/// Runs the system with the given input in the world.
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fn run(&mut self, input: Self::In, world: &mut World) -> Self::Out {
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// SAFE: world and resources are exclusively borrowed
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unsafe { self.run_unsafe(input, world) }
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}
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fn apply_buffers(&mut self, world: &mut World);
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/// Initialize the system.
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fn initialize(&mut self, _world: &mut World);
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fn check_change_tick(&mut self, change_tick: u32);
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}
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/// A convenience type alias for a boxed [`System`] trait object.
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pub type BoxedSystem<In = (), Out = ()> = Box<dyn System<In = In, Out = Out>>;
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pub(crate) fn check_system_change_tick(
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last_change_tick: &mut u32,
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change_tick: u32,
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system_name: &str,
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) {
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let tick_delta = change_tick.wrapping_sub(*last_change_tick);
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const MAX_DELTA: u32 = (u32::MAX / 4) * 3;
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// Clamp to max delta
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if tick_delta > MAX_DELTA {
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warn!(
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"Too many intervening systems have run since the last time System '{}' was last run; it may fail to detect changes.",
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system_name
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);
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*last_change_tick = change_tick.wrapping_sub(MAX_DELTA);
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}
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}
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