bevy_ecs/message/
message_registry.rs

1use crate::{
2    change_detection::{DetectChangesMut, MutUntyped},
3    component::{ComponentId, Tick},
4    message::{Message, Messages},
5    resource::Resource,
6    world::World,
7};
8use alloc::vec::Vec;
9
10#[doc(hidden)]
11struct RegisteredMessage {
12    messages_component: ComponentId,
13    // Required to flush the secondary buffer and drop messages even if left unchanged.
14    previously_updated: bool,
15    // SAFETY: The message's component ID and the function must be used to fetch the Messages<T> resource
16    // of the same type initialized in `register_message`, or improper type casts will occur.
17    update: unsafe fn(MutUntyped),
18}
19
20/// A registry of all of the [`Messages`] in the [`World`], used by [`message_update_system`](crate::message::message_update_system)
21/// to update all of the messages.
22#[derive(Resource, Default)]
23pub struct MessageRegistry {
24    /// Should the messages be updated?
25    ///
26    /// This field is generally automatically updated by the [`signal_message_update_system`](crate::message::signal_message_update_system).
27    pub should_update: ShouldUpdateMessages,
28    message_updates: Vec<RegisteredMessage>,
29}
30
31/// Controls whether or not the messages in an [`MessageRegistry`] should be updated.
32#[derive(Default, Debug, Clone, Copy, PartialEq, Eq)]
33pub enum ShouldUpdateMessages {
34    /// Without any fixed timestep, messages should always be updated each frame.
35    #[default]
36    Always,
37    /// We need to wait until at least one pass of the fixed update schedules to update the messages.
38    Waiting,
39    /// At least one pass of the fixed update schedules has occurred, and the messages are ready to be updated.
40    Ready,
41}
42
43impl MessageRegistry {
44    /// Registers a message type to be updated in a given [`World`]
45    ///
46    /// If no instance of the [`MessageRegistry`] exists in the world, this will add one - otherwise it will use
47    /// the existing instance.
48    pub fn register_message<T: Message>(world: &mut World) {
49        // By initializing the resource here, we can be sure that it is present,
50        // and receive the correct, up-to-date `ComponentId` even if it was previously removed.
51        let component_id = world.init_resource::<Messages<T>>();
52        let mut registry = world.get_resource_or_init::<Self>();
53        registry.message_updates.push(RegisteredMessage {
54            messages_component: component_id,
55            previously_updated: false,
56            update: |ptr| {
57                // SAFETY: The resource was initialized with the type Messages<T>.
58                unsafe { ptr.with_type::<Messages<T>>() }
59                    .bypass_change_detection()
60                    .update();
61            },
62        });
63    }
64
65    /// Updates all of the registered messages in the World.
66    pub fn run_updates(&mut self, world: &mut World, last_change_tick: Tick) {
67        for registered_message in &mut self.message_updates {
68            // Bypass the type ID -> Component ID lookup with the cached component ID.
69            if let Some(messages) =
70                world.get_resource_mut_by_id(registered_message.messages_component)
71            {
72                let has_changed = messages.has_changed_since(last_change_tick);
73                if registered_message.previously_updated || has_changed {
74                    // SAFETY: The update function pointer is called with the resource
75                    // fetched from the same component ID.
76                    unsafe { (registered_message.update)(messages) };
77                    // Always set to true if the messages have changed, otherwise disable running on the second invocation
78                    // to wait for more changes.
79                    registered_message.previously_updated =
80                        has_changed || !registered_message.previously_updated;
81                }
82            }
83        }
84    }
85
86    /// Removes a message from the world and its associated [`MessageRegistry`].
87    pub fn deregister_messages<T: Message>(world: &mut World) {
88        let component_id = world.init_resource::<Messages<T>>();
89        let mut registry = world.get_resource_or_init::<Self>();
90        registry
91            .message_updates
92            .retain(|e| e.messages_component != component_id);
93        world.remove_resource::<Messages<T>>();
94    }
95}
bevy_ecs/message/message_registry.rs

bevy_ecs/message/
message_registry.rs
