684f07595f
# Objective Complete the first part of the migration detailed in bevyengine/rfcs#45. ## Solution Add all the new stuff. ### TODO - [x] Impl tuple methods. - [x] Impl chaining. - [x] Port ambiguity detection. - [x] Write docs. - [x] ~~Write more tests.~~(will do later) - [ ] Write changelog and examples here? - [x] ~~Replace `petgraph`.~~ (will do later) Co-authored-by: james7132 <contact@jamessliu.com> Co-authored-by: Michael Hsu <mike.hsu@gmail.com> Co-authored-by: Mike Hsu <mike.hsu@gmail.com>
65 lines
2.5 KiB
Rust
65 lines
2.5 KiB
Rust
use std::fmt::Debug;
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use std::hash::Hash;
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use std::mem;
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use crate as bevy_ecs;
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use crate::schedule_v3::{ScheduleLabel, SystemSet, WorldExt};
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use crate::system::Resource;
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use crate::world::World;
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/// Types that can define states in a finite-state machine.
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pub trait States: 'static + Send + Sync + Clone + PartialEq + Eq + Hash + Debug {
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type Iter: Iterator<Item = Self>;
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/// Returns an iterator over all the state variants.
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fn states() -> Self::Iter;
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}
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/// The label of a [`Schedule`](super::Schedule) that runs whenever [`State<S>`]
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/// enters this state.
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#[derive(ScheduleLabel, Clone, Debug, PartialEq, Eq, Hash)]
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pub struct OnEnter<S: States>(pub S);
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/// The label of a [`Schedule`](super::Schedule) that runs whenever [`State<S>`]
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/// exits this state.
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#[derive(ScheduleLabel, Clone, Debug, PartialEq, Eq, Hash)]
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pub struct OnExit<S: States>(pub S);
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/// A [`SystemSet`] that will run within \<insert-`bevy_core`-set-name\> when this state is active.
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///
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/// This is provided for convenience. A more general [`state_equals`](super::state_equals)
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/// [condition](super::Condition) also exists for systems that need to run elsewhere.
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#[derive(SystemSet, Clone, Debug, PartialEq, Eq, Hash)]
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pub struct OnUpdate<S: States>(pub S);
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/// A finite-state machine whose transitions have associated schedules
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/// ([`OnEnter(state)`] and [`OnExit(state)`]).
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///
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/// The current state value can be accessed through this resource. To *change* the state,
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/// queue a transition in the [`NextState<S>`] resource, and it will be applied by the next
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/// [`apply_state_transition::<S>`] system.
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#[derive(Resource)]
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pub struct State<S: States>(pub S);
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/// The next state of [`State<S>`].
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///
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/// To queue a transition, just set the contained value to `Some(next_state)`.
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#[derive(Resource)]
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pub struct NextState<S: States>(pub Option<S>);
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/// If a new state is queued in [`NextState<S>`], this system:
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/// - Takes the new state value from [`NextState<S>`] and updates [`State<S>`].
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/// - Runs the [`OnExit(exited_state)`] schedule.
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/// - Runs the [`OnEnter(entered_state)`] schedule.
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pub fn apply_state_transition<S: States>(world: &mut World) {
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if world.resource::<NextState<S>>().0.is_some() {
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let entered_state = world.resource_mut::<NextState<S>>().0.take().unwrap();
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let exited_state = mem::replace(
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&mut world.resource_mut::<State<S>>().0,
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entered_state.clone(),
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);
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world.run_schedule(OnExit(exited_state));
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world.run_schedule(OnEnter(entered_state));
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}
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}
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