azalea_entity/plugin/
relative_updates.rs

1// How entity updates are processed (to avoid issues with shared worlds)
2// - each bot contains a map of { entity id: updates received }
3// - the shared world also contains a canonical "true" updates received for each
4//   entity
5// - when a client loads an entity, its "updates received" is set to the same as
6//   the global "updates received"
7// - when the shared world sees an entity for the first time, the "updates
8//   received" is set to 1.
9// - clients can force the shared "updates received" to 0 to make it so certain
10//   entities (i.e. other bots in our swarm) don't get confused and updated by
11//   other bots
12// - when a client gets an update to an entity, we check if our "updates
13//   received" is the same as the shared world's "updates received": if it is,
14//   then process the update and increment the client's and shared world's
15//   "updates received" if not, then we simply increment our local "updates
16//   received" and do nothing else
17
18use std::sync::Arc;
19
20use azalea_world::{MinecraftEntityId, PartialInstance};
21use bevy_ecs::prelude::*;
22use derive_more::{Deref, DerefMut};
23use parking_lot::RwLock;
24use tracing::warn;
25
26use crate::LocalEntity;
27
28/// An [`EntityCommand`] that applies a "relative update" to an entity, which
29/// means this update won't be run multiple times by different clients in the
30/// same world.
31///
32/// This is used to avoid a bug where when there's multiple clients in the same
33/// world and an entity sends a relative move packet to all clients, its
34/// position gets desynced since the relative move is applied multiple times.
35///
36/// Don't use this unless you actually got an entity update packet that all
37/// other clients within render distance will get too. You usually don't need
38/// this when the change isn't relative either.
39pub struct RelativeEntityUpdate {
40    pub partial_world: Arc<RwLock<PartialInstance>>,
41    // a function that takes the entity and updates it
42    pub update: Box<dyn FnOnce(&mut EntityWorldMut) + Send + Sync>,
43}
44impl RelativeEntityUpdate {
45    pub fn new(
46        partial_world: Arc<RwLock<PartialInstance>>,
47        update: impl FnOnce(&mut EntityWorldMut) + Send + Sync + 'static,
48    ) -> Self {
49        Self {
50            partial_world,
51            update: Box::new(update),
52        }
53    }
54}
55
56/// A component that counts the number of times this entity has been modified.
57/// This is used for making sure two clients don't do the same relative update
58/// on an entity.
59///
60/// If an entity is local (i.e. it's a client/LocalEntity), this component
61/// should NOT be present in the entity.
62#[derive(Component, Debug, Deref, DerefMut)]
63pub struct UpdatesReceived(u32);
64
65impl EntityCommand for RelativeEntityUpdate {
66    fn apply(self, mut entity: EntityWorldMut) {
67        let partial_entity_infos = &mut self.partial_world.write().entity_infos;
68
69        if Some(entity.id()) == partial_entity_infos.owner_entity {
70            // if the entity owns this partial world, it's always allowed to update itself
71            (self.update)(&mut entity);
72            return;
73        };
74
75        let entity_id = *entity.get::<MinecraftEntityId>().unwrap();
76        if entity.contains::<LocalEntity>() {
77            // a client tried to update another client, which isn't allowed
78            return;
79        }
80
81        let this_client_updates_received = partial_entity_infos
82            .updates_received
83            .get(&entity_id)
84            .copied();
85
86        let can_update = if let Some(updates_received) = entity.get::<UpdatesReceived>() {
87            this_client_updates_received.unwrap_or(1) == **updates_received
88        } else {
89            // no UpdatesReceived means the entity was just spawned
90            true
91        };
92        if can_update {
93            let new_updates_received = this_client_updates_received.unwrap_or(0) + 1;
94            partial_entity_infos
95                .updates_received
96                .insert(entity_id, new_updates_received);
97
98            entity.insert(UpdatesReceived(new_updates_received));
99
100            (self.update)(&mut entity);
101        }
102    }
103}
104
105/// The [`UpdatesReceived`] component should never be on [`LocalEntity`]
106/// entities. This warns if an entity has both components.
107pub fn debug_detect_updates_received_on_local_entities(
108    query: Query<Entity, (With<LocalEntity>, With<UpdatesReceived>)>,
109) {
110    for entity in &query {
111        warn!(
112            "Entity {:?} has both LocalEntity and UpdatesReceived",
113            entity
114        );
115    }
116}
azalea_entity/plugin/relative_updates.rs

azalea_entity/plugin/
relative_updates.rs
