From 80cac4083b334e8397cef467e49171716736c2d8 Mon Sep 17 00:00:00 2001
From: Martin Indra <martin.indra@mgn.cz>
Date: Tue, 19 Sep 2023 21:32:12 +0200
Subject: [PATCH] Multiplayer: impl transform syncing (#736)

---
 Cargo.lock                          |   3 +
 crates/movement/Cargo.toml          |   7 +-
 crates/movement/src/lib.rs          |   3 +
 crates/movement/src/syncing.rs      | 112 ++++++++++++++++++++++++++++
 crates/multiplayer/src/lib.rs       |   2 +-
 crates/multiplayer/src/playermsg.rs |  34 ++++++++-
 6 files changed, 156 insertions(+), 5 deletions(-)
 create mode 100644 crates/movement/src/syncing.rs

diff --git a/Cargo.lock b/Cargo.lock
index 9fc421c40..5f37820be 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2537,9 +2537,12 @@ dependencies = [
  "de_core",
  "de_index",
  "de_map",
+ "de_messages",
+ "de_multiplayer",
  "de_objects",
  "de_pathing",
  "de_types",
+ "fastrand 1.9.0",
  "glam",
  "parry2d",
  "parry3d",
diff --git a/crates/movement/Cargo.toml b/crates/movement/Cargo.toml
index bdac1f27b..b2b180972 100644
--- a/crates/movement/Cargo.toml
+++ b/crates/movement/Cargo.toml
@@ -16,12 +16,15 @@ categories.workspace = true
 de_core.workspace = true
 de_index.workspace = true
 de_map.workspace = true
+de_messages.workspace = true
+de_multiplayer.workspace = true
 de_objects.workspace = true
 de_pathing.workspace = true
 de_types.workspace = true
 
 # Other
 bevy.workspace = true
-parry3d.workspace = true
-parry2d.workspace = true
+fastrand.workspace = true
 glam.workspace = true
+parry2d.workspace = true
+parry3d.workspace = true
diff --git a/crates/movement/src/lib.rs b/crates/movement/src/lib.rs
index 67e5a5a80..559b58f5a 100644
--- a/crates/movement/src/lib.rs
+++ b/crates/movement/src/lib.rs
@@ -6,6 +6,7 @@ mod movement;
 mod obstacles;
 mod pathing;
 mod repulsion;
+mod syncing;
 
 use std::f32::consts::PI;
 
@@ -16,6 +17,7 @@ use movement::MovementPlugin;
 use obstacles::ObstaclesPlugin;
 use pathing::PathingPlugin;
 use repulsion::RepulsionPlugin;
+use syncing::SyncingPlugin;
 
 /// Maximum object horizontal speed in meters per second.
 const MAX_H_SPEED: f32 = 10.;
@@ -43,5 +45,6 @@ impl PluginGroup for MovementPluginGroup {
             .add(RepulsionPlugin)
             .add(KinematicsPlugin)
             .add(AltitudePlugin)
+            .add(SyncingPlugin)
     }
 }
diff --git a/crates/movement/src/syncing.rs b/crates/movement/src/syncing.rs
new file mode 100644
index 000000000..b85d4cc30
--- /dev/null
+++ b/crates/movement/src/syncing.rs
@@ -0,0 +1,112 @@
+use std::time::Duration;
+
+use bevy::prelude::*;
+use de_core::{
+    gamestate::GameState,
+    gconfig::GameConfig,
+    objects::{Local, MovableSolid},
+    schedule::{Movement, PreMovement},
+    state::AppState,
+};
+use de_messages::ToPlayers;
+use de_multiplayer::{NetEntities, NetRecvTransformEvent, ToPlayersEvent};
+
+use crate::movement::MovementSet;
+
+const MIN_SYNC_PERIOD: Duration = Duration::from_secs(2);
+const SYNC_RANDOMIZATION_MS: u64 = 2_000;
+
+pub(crate) struct SyncingPlugin;
+
+impl Plugin for SyncingPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(
+            PreMovement,
+            setup_entities
+                .run_if(is_multiplayer)
+                .run_if(in_state(AppState::InGame)),
+        )
+        .add_systems(
+            Movement,
+            (
+                receive_transforms
+                    .run_if(on_event::<NetRecvTransformEvent>())
+                    .after(MovementSet::UpdateTransform),
+                send_transforms
+                    .run_if(is_multiplayer)
+                    .after(MovementSet::UpdateTransform),
+            )
+                .run_if(in_state(GameState::Playing)),
+        );
+    }
+}
+
+#[derive(Component)]
+struct SyncTimer(Duration);
+
+impl SyncTimer {
+    fn schedule(time: Duration) -> Duration {
+        let jitter = Duration::from_millis(fastrand::u64(0..SYNC_RANDOMIZATION_MS));
+        time + MIN_SYNC_PERIOD + jitter
+    }
+
+    fn new(time: Duration) -> Self {
+        Self(Self::schedule(time))
+    }
+
+    /// Sets sync expiration to the future relative to the current time.
+    fn refresh(&mut self, time: Duration) {
+        self.0 = Self::schedule(time);
+    }
+
+    /// Returns true if transform sync is already due.
+    fn outdated(&self, time: Duration) -> bool {
+        time >= self.0
+    }
+}
+
+type NotSetUp = (With<MovableSolid>, With<Local>, Without<SyncTimer>);
+
+fn is_multiplayer(config: Option<Res<GameConfig>>) -> bool {
+    match config {
+        Some(config) => config.multiplayer(),
+        None => false,
+    }
+}
+
+fn setup_entities(mut commands: Commands, time: Res<Time>, entities: Query<Entity, NotSetUp>) {
+    let time = time.elapsed();
+    for entity in entities.iter() {
+        commands.entity(entity).insert(SyncTimer::new(time));
+    }
+}
+
+fn receive_transforms(
+    mut entities: Query<&mut Transform>,
+    mut events: EventReader<NetRecvTransformEvent>,
+) {
+    for event in events.iter() {
+        if let Ok(mut transform) = entities.get_mut(event.entity()) {
+            *transform = event.transform();
+        }
+    }
+}
+
+fn send_transforms(
+    time: Res<Time>,
+    net_entities: NetEntities,
+    mut entities: Query<(Entity, &mut SyncTimer, &Transform)>,
+    mut net_events: EventWriter<ToPlayersEvent>,
+) {
+    let time = time.elapsed();
+    for (entity, mut sync, transform) in entities.iter_mut() {
+        if sync.outdated(time) {
+            sync.refresh(time);
+
+            net_events.send(ToPlayersEvent::new(ToPlayers::Transform {
+                entity: net_entities.local_net_id(entity),
+                transform: transform.into(),
+            }));
+        }
+    }
+}
diff --git a/crates/multiplayer/src/lib.rs b/crates/multiplayer/src/lib.rs
index ba943acf0..2d6b989d4 100644
--- a/crates/multiplayer/src/lib.rs
+++ b/crates/multiplayer/src/lib.rs
@@ -25,7 +25,7 @@ pub use crate::{
     netstate::NetState,
     playermsg::{
         GameNetSet, NetEntities, NetEntityCommands, NetRecvDespawnActiveEvent, NetRecvHealthEvent,
-        NetRecvSpawnActiveEvent,
+        NetRecvSpawnActiveEvent, NetRecvTransformEvent,
     },
 };
 use crate::{netstate::NetStatePlugin, network::NetworkPlugin};
diff --git a/crates/multiplayer/src/playermsg.rs b/crates/multiplayer/src/playermsg.rs
index 77ecb0304..967e633bb 100644
--- a/crates/multiplayer/src/playermsg.rs
+++ b/crates/multiplayer/src/playermsg.rs
@@ -17,6 +17,7 @@ impl Plugin for PlayerMsgPlugin {
         app.add_event::<NetRecvSpawnActiveEvent>()
             .add_event::<NetRecvDespawnActiveEvent>()
             .add_event::<NetRecvHealthEvent>()
+            .add_event::<NetRecvTransformEvent>()
             .add_systems(OnEnter(AppState::InGame), setup)
             .add_systems(OnExit(AppState::InGame), cleanup)
             .add_systems(
@@ -124,6 +125,26 @@ impl NetRecvHealthEvent {
     }
 }
 
+#[derive(Event)]
+pub struct NetRecvTransformEvent {
+    entity: Entity,
+    transform: Transform,
+}
+
+impl NetRecvTransformEvent {
+    fn new(entity: Entity, transform: Transform) -> Self {
+        Self { entity, transform }
+    }
+
+    pub fn entity(&self) -> Entity {
+        self.entity
+    }
+
+    pub fn transform(&self) -> Transform {
+        self.transform
+    }
+}
+
 #[derive(SystemParam)]
 pub struct NetEntities<'w> {
     config: Res<'w, GameConfig>,
@@ -172,10 +193,13 @@ impl<'w> NetEntityCommands<'w> {
     }
 
     fn local_id(&self, entity: EntityNet) -> Option<Entity> {
-        self.map
-            .translate_remote(entity)
+        self.remote_local_id(entity)
             .or_else(|| self.entities.resolve_from_id(entity.index().into()))
     }
+
+    fn remote_local_id(&self, entity: EntityNet) -> Option<Entity> {
+        self.map.translate_remote(entity)
+    }
 }
 
 /// Mapping between remote and local entity IDs for non-locally simulated
@@ -305,6 +329,7 @@ fn recv_messages(
     mut inputs: EventReader<FromPlayersEvent>,
     mut spawn_events: EventWriter<NetRecvSpawnActiveEvent>,
     mut despawn_events: EventWriter<NetRecvDespawnActiveEvent>,
+    mut transform_events: EventWriter<NetRecvTransformEvent>,
     mut health_events: EventWriter<NetRecvHealthEvent>,
 ) {
     for input in inputs.iter() {
@@ -329,6 +354,11 @@ fn recv_messages(
                 let local = net_commands.deregister(*entity);
                 despawn_events.send(NetRecvDespawnActiveEvent::new(local));
             }
+            ToPlayers::Transform { entity, transform } => {
+                if let Some(local) = net_commands.remote_local_id(*entity) {
+                    transform_events.send(NetRecvTransformEvent::new(local, transform.into()));
+                }
+            }
             ToPlayers::ChangeHealth { entity, delta } => {
                 let Some(local) = net_commands.local_id(*entity) else {
                     warn!("Received net health update of unrecognized entity: {entity:?}");