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//! Extension system utilities.
//!
//! This modules contains an extension trait for the System trait which adds useful transformation
//! functions.
use crate::{
ecs::prelude::{Read, System, World},
shred::{RunningTime, SystemData},
};
#[cfg(feature = "profiler")]
use thread_profiler::profile_scope;
/// Extension functionality associated systems.
pub trait SystemExt {
/// Make a system pausable by tying it to a specific value of a resource.
///
/// When the value of the resource differs from `value` the system is considered "paused",
/// and the `run` method of the pausable system will not be called.
///
/// # Notes
///
/// Special care must be taken not to read from an `EventChannel` with pausable systems.
/// Since `run` is never called, there is no way to consume the reader side of a channel, and
/// it may grow indefinitely leaking memory while the system is paused.
///
/// # Examples
///
/// ```rust
/// use amethyst::{
/// ecs::{System, Write},
/// shred::DispatcherBuilder,
/// prelude::*,
/// };
///
/// #[derive(PartialEq)]
/// enum CurrentState {
/// Disabled,
/// Enabled,
/// }
///
/// impl Default for CurrentState {
/// fn default() -> Self {
/// CurrentState::Disabled
/// }
/// }
///
/// struct AddNumber(u32);
///
/// impl<'s> System<'s> for AddNumber {
/// type SystemData = Write<'s, u32>;
///
/// fn run(&mut self, mut number: Self::SystemData) {
/// *number += self.0;
/// }
/// }
///
/// let mut world = World::new();
///
/// let mut dispatcher = DispatcherBuilder::default()
/// .with(AddNumber(1), "set_number", &[])
/// .with(AddNumber(2).pausable(CurrentState::Enabled), "set_number_2", &[])
/// .build();
///
/// dispatcher.setup(&mut world);
///
/// // we only expect the u32 resource to be modified _if_ the system is enabled,
/// // the system should only be enabled on CurrentState::Enabled.
///
/// *world.write_resource() = 0u32;
/// dispatcher.dispatch(&mut world);
/// assert_eq!(1, *world.read_resource::<u32>());
///
/// *world.write_resource() = 0u32;
/// *world.write_resource() = CurrentState::Enabled;
/// dispatcher.dispatch(&mut world);
/// assert_eq!(1 + 2, *world.read_resource::<u32>());
/// ```
fn pausable<V: 'static>(self, value: V) -> Pausable<Self, V>
where
Self: Sized,
V: Send + Sync + Default + PartialEq;
}
impl<'s, S> SystemExt for S
where
S: System<'s>,
{
fn pausable<V: 'static>(self, value: V) -> Pausable<Self, V>
where
Self: Sized,
V: Send + Sync + Default + PartialEq,
{
Pausable {
system: self,
value,
}
}
}
/// A system that is enabled when `V` has a specific value.
///
/// This is created using the [`SystemExt::pausable`] method.
///
/// [`SystemExt::pausable`]: trait.SystemExt.html#tymethod.pausable
#[derive(Debug)]
pub struct Pausable<S, V> {
system: S,
value: V,
}
impl<'s, S, V: 'static> System<'s> for Pausable<S, V>
where
S::SystemData: SystemData<'s>,
S: System<'s>,
V: Send + Sync + Default + PartialEq,
{
type SystemData = (Read<'s, V>, S::SystemData);
fn run(&mut self, data: Self::SystemData) {
#[cfg(feature = "profiler")]
profile_scope!("pauseable_system");
if self.value != *data.0 {
return;
}
self.system.run(data.1);
}
fn running_time(&self) -> RunningTime {
self.system.running_time()
}
fn setup(&mut self, world: &mut World) {
Self::SystemData::setup(world);
self.system.setup(world);
}
}