From d4427832f098a3197be40219830627dc50e1f5de Mon Sep 17 00:00:00 2001
From: Maxicarlos08 <maxicarlos08@gmail.com>
Date: Fri, 29 Sep 2023 22:33:24 +0200
Subject: [PATCH] Update rtsim vehicle position on unload

---
 server/src/lib.rs       |  8 ++++----
 server/src/rtsim/mod.rs | 19 ++++++++++++++++++-
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/server/src/lib.rs b/server/src/lib.rs
index ce54a4e997..477abcf774 100644
--- a/server/src/lib.rs
+++ b/server/src/lib.rs
@@ -861,7 +861,7 @@ impl Server {
                         None => terrain.get_key_real(chunk_key).is_none(),
                     }
                 })
-                .map(|(entity, _, _, _, _)| entity)
+                .map(|(entity, pos, _, _, _)| (entity, pos.0))
                 .collect::<Vec<_>>()
         };
 
@@ -869,14 +869,14 @@ impl Server {
             let rtsim_vehicles = self.state.ecs().read_storage::<RtSimVehicle>();
 
             // Assimilate entities that are part of the real-time world simulation
-            for entity in &to_delete {
+            for (entity, pos) in &to_delete {
                 #[cfg(feature = "worldgen")]
                 if let Some(rtsim_entity) = rtsim_entities.get(*entity) {
                     rtsim.hook_rtsim_entity_unload(*rtsim_entity);
                 }
                 #[cfg(feature = "worldgen")]
                 if let Some(rtsim_vehicle) = rtsim_vehicles.get(*entity) {
-                    rtsim.hook_rtsim_vehicle_unload(*rtsim_vehicle);
+                    rtsim.hook_rtsim_vehicle_unload(*rtsim_vehicle, *pos);
                 }
             }
         }
@@ -884,7 +884,7 @@ impl Server {
         drop(rtsim);
 
         // Actually perform entity deletion
-        for entity in to_delete {
+        for (entity, _) in to_delete {
             if let Err(e) = self.state.delete_entity_recorded(entity) {
                 error!(?e, "Failed to delete agent outside the terrain");
             }
diff --git a/server/src/rtsim/mod.rs b/server/src/rtsim/mod.rs
index d92dc95369..cf30cb1546 100644
--- a/server/src/rtsim/mod.rs
+++ b/server/src/rtsim/mod.rs
@@ -194,9 +194,26 @@ impl RtSim {
             .unwrap_or(true)
     }
 
-    pub fn hook_rtsim_vehicle_unload(&mut self, entity: RtSimVehicle) {
+    pub fn hook_rtsim_vehicle_unload(&mut self, entity: RtSimVehicle, pos: Vec3<f32>) {
         let data = self.state.get_data_mut();
         if let Some(vehicle) = data.npcs.vehicles.get_mut(entity.0) {
+            // If we do not update the vehicle's position here the following bug will occur:
+            // -- tick start, rtsim system hasn't ran yet
+            // The server filters out any entities that have left the player's view
+            // distance, including this ship. These entities are then removed from the ECS,
+            // except for RtSim riders which are set to SimulationMode::Simulated (the
+            // rtsim system is responsible for cleaning this up).
+            // However when the RtSim system runs afterwards, it detects that the position
+            // of the *previous* tick is still in view distance! (positions for
+            // rtsim2 vehiclces are only updated for entities present in the
+            // ECS, but the ship was just removed).
+            // Now the ship is loaded again (in the same tick), and a new captain
+            // with it (note that the old one hasn't been despawned, just set to
+            // SimulationMode::Simulated wich is overwritten in the vehicle loading
+            // anyways).
+            // Result: The ship stays in loaded for one more tick and we now have 2 captains
+            // (one unmanaged by RtSim, having the default unloading behaviour)
+            vehicle.wpos = pos;
             vehicle.mode = SimulationMode::Simulated;
             if let Some(Actor::Npc(npc)) = vehicle.driver {
                 if let Some(npc) = data.npcs.get_mut(npc) {