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::{
22    prelude::{Component, Entity},
23    query::With,
24    system::{EntityCommand, Query},
25    world::{EntityWorldMut, World},
26};
27use derive_more::{Deref, DerefMut};
28use parking_lot::RwLock;
29use tracing::warn;
30
31use crate::LocalEntity;
32
33/// An [`EntityCommand`] that applies a "relative update" to an entity, which
34/// means this update won't be run multiple times by different clients in the
35/// same world.
36///
37/// This is used to avoid a bug where when there's multiple clients in the same
38/// world and an entity sends a relative move packet to all clients, its
39/// position gets desynced since the relative move is applied multiple times.
40///
41/// Don't use this unless you actually got an entity update packet that all
42/// other clients within render distance will get too. You usually don't need
43/// this when the change isn't relative either.
44pub struct RelativeEntityUpdate {
45    pub partial_world: Arc<RwLock<PartialInstance>>,
46    // a function that takes the entity and updates it
47    pub update: Box<dyn FnOnce(&mut EntityWorldMut) + Send + Sync>,
48}
49impl RelativeEntityUpdate {
50    pub fn new(
51        partial_world: Arc<RwLock<PartialInstance>>,
52        update: impl FnOnce(&mut EntityWorldMut) + Send + Sync + 'static,
53    ) -> Self {
54        Self {
55            partial_world,
56            update: Box::new(update),
57        }
58    }
59}
60
61/// A component that counts the number of times this entity has been modified.
62/// This is used for making sure two clients don't do the same relative update
63/// on an entity.
64///
65/// If an entity is local (i.e. it's a client/LocalEntity), this component
66/// should NOT be present in the entity.
67#[derive(Component, Debug, Deref, DerefMut)]
68pub struct UpdatesReceived(u32);
69
70impl EntityCommand for RelativeEntityUpdate {
71    fn apply(self, entity: Entity, world: &mut World) {
72        let partial_entity_infos = &mut self.partial_world.write().entity_infos;
73
74        let mut entity_mut = world.entity_mut(entity);
75
76        if Some(entity) == partial_entity_infos.owner_entity {
77            // if the entity owns this partial world, it's always allowed to update itself
78            (self.update)(&mut entity_mut);
79            return;
80        };
81
82        let entity_id = *entity_mut.get::<MinecraftEntityId>().unwrap();
83        if entity_mut.contains::<LocalEntity>() {
84            // a client tried to update another client, which isn't allowed
85            return;
86        }
87
88        let this_client_updates_received = partial_entity_infos
89            .updates_received
90            .get(&entity_id)
91            .copied();
92
93        let can_update = if let Some(updates_received) = entity_mut.get::<UpdatesReceived>() {
94            this_client_updates_received.unwrap_or(1) == **updates_received
95        } else {
96            // no UpdatesReceived means the entity was just spawned
97            true
98        };
99        if can_update {
100            let new_updates_received = this_client_updates_received.unwrap_or(0) + 1;
101            partial_entity_infos
102                .updates_received
103                .insert(entity_id, new_updates_received);
104
105            entity_mut.insert(UpdatesReceived(new_updates_received));
106
107            let mut entity = world.entity_mut(entity);
108            (self.update)(&mut entity);
109        }
110    }
111}
112
113/// The [`UpdatesReceived`] component should never be on [`LocalEntity`]
114/// entities. This warns if an entity has both components.
115pub fn debug_detect_updates_received_on_local_entities(
116    query: Query<Entity, (With<LocalEntity>, With<UpdatesReceived>)>,
117) {
118    for entity in &query {
119        warn!(
120            "Entity {:?} has both LocalEntity and UpdatesReceived",
121            entity
122        );
123    }
124}
azalea_entity/plugin/relative_updates.rs

azalea_entity/plugin/
relative_updates.rs
