From 0494c19c47fcf26382f055c658e7c2c9d737b55a Mon Sep 17 00:00:00 2001
From: ghostly_zsh <ghostly@e3t.cc>
Date: Thu, 11 Jun 2026 17:54:21 -0500
Subject: [PATCH] netcode fix: dumb stupid interpolation works when there's no
 inconsistent delay or loss or reordering of packets

---
 crates/unified/src/client/interpolation.rs    | 64 +++++++++++++++----
 crates/unified/src/client/mod.rs              |  2 +-
 crates/unified/src/client/parts.rs            | 15 +++--
 .../src/client/planet/incoming_planets.rs     | 17 ++++-
 crates/unified/src/shared/net.rs              |  4 +-
 5 files changed, 81 insertions(+), 21 deletions(-)

diff --git a/crates/unified/src/client/interpolation.rs b/crates/unified/src/client/interpolation.rs
index 065101db071c640ca6aa461d74641990f68921cb..4809501c94fc15d008e636346aabaf1077d3a7aa 100644
--- a/crates/unified/src/client/interpolation.rs
+++ b/crates/unified/src/client/interpolation.rs
@@ -1,3 +1,4 @@
+use std::f32::consts::PI;
 use std::time::{Duration};
 use avian2d::parry::transformation::utils::transform;
 use crate::prelude::*;
@@ -5,34 +6,71 @@ use crate::prelude::*;
 pub fn interpolation_plugin(app: &mut App) {
     app
         .add_systems(Update, update_interpolation_info)
+        .add_systems(Update, sync_non_interpolated_transforms)
         .add_systems(Update, do_interpolation);
 }
 
 #[derive(Component, Debug)]
-pub struct TransformInterpolationInfo {
+pub struct TranslationInterpolationInfo {
     pub last_dt: Duration,
     pub this_tick_start: bevy::platform::time::Instant,
-    pub latest_transform: Transform,
-    pub last_transform: Transform,
+    pub latest_position: Vec2,
+    pub last_position: Vec2,
+}
+#[derive(Component, Debug)]
+pub struct RotationInterpolationInfo {
+    pub last_dt: Duration,
+    pub this_tick_start: bevy::platform::time::Instant,
+    pub last_angular_velocity: f32,
+    pub latest_rotation: f32,
+    pub last_rotation: f32,
 }
 
 fn update_interpolation_info(
-    mut interpolation_query: Query<(&Transform, &mut TransformInterpolationInfo), Changed<Transform>>,
-    time: Res<Time>,
+    mut interpolation_pos_query: Query<(Entity, &Position, &mut TranslationInterpolationInfo), Changed<Position>>,
+    mut interpolation_rot_query: Query<(&Rotation, &AngularVelocity, &mut RotationInterpolationInfo), Changed<Rotation>>,
 ) {
-    for (transform, mut info) in interpolation_query.iter_mut() {
+    for (entity, position, mut info) in interpolation_pos_query.iter_mut() {
         info.last_dt = info.this_tick_start.elapsed();
         info.this_tick_start = bevy::platform::time::Instant::now();
-        info.last_transform = info.latest_transform;
-        info.latest_transform = transform.clone();
+        info.last_position = info.latest_position;
+        info.latest_position = position.as_vec2();
+    }
+    for (rotation, angular_velocity, mut info) in interpolation_rot_query.iter_mut() {
+        info.last_dt = info.this_tick_start.elapsed();
+        info.this_tick_start = bevy::platform::time::Instant::now();
+        let avg_angular_velocity = (angular_velocity.0.val_num_f32() + info.last_angular_velocity) / 2.0;
+        let delta_rotation = avg_angular_velocity * info.last_dt.as_secs_f32();
+        let num_revolutions = (delta_rotation / (2.0*PI)).round();
+        info.last_rotation = info.latest_rotation;
+        let mut rotation_offset = 0.0;
+        let rotation = rotation.as_radians().val_num_f32();
+        if delta_rotation + info.last_rotation >= PI {
+            rotation_offset = 2.0*PI;
+        } else if delta_rotation + info.last_rotation < -PI {
+            rotation_offset = -2.0*PI;
+        }
+        info.latest_rotation = rotation + rotation_offset + num_revolutions*2.0*PI;
+        info.last_angular_velocity = angular_velocity.0.val_num_f32();
+    }
+}
+fn sync_non_interpolated_transforms(
+    mut query: Query<(&mut Transform, &Position), (Changed<Position>, Without<TranslationInterpolationInfo>)>,
+) {
+    for (mut transform, position) in &mut query {
+        transform.translation = position.as_vec2().extend(0.0);
     }
 }
 fn do_interpolation(
-    mut interpolation_query: Query<(&mut Transform, &TransformInterpolationInfo)>,
+    mut interpolation_query: Query<(Entity, &mut Transform, &TranslationInterpolationInfo, &RotationInterpolationInfo)>,
 ) {
-    for (mut transform, info) in &mut interpolation_query {
-        let dt = bevy::platform::time::Instant::now() - info.this_tick_start;
-        let progress = dt.as_secs_f32() / info.last_dt.as_secs_f32(); // should be between 0.0 and 1.0
-        transform.bypass_change_detection().translation = info.last_transform.translation + progress * (info.latest_transform.translation - info.last_transform.translation);
+    for (entity, mut transform, pos_info, rot_info) in &mut interpolation_query {
+        let dt = bevy::platform::time::Instant::now() - pos_info.this_tick_start;
+        let progress = dt.as_secs_f32() / pos_info.last_dt.as_secs_f32(); // should be between 0.0 and 1.0
+        transform.translation = (pos_info.last_position + progress * (pos_info.latest_position - pos_info.last_position)).extend(0.0);
+
+        let dt = bevy::platform::time::Instant::now() - rot_info.this_tick_start;
+        let progress = dt.as_secs_f32() / rot_info.last_dt.as_secs_f32(); // should be between 0.0 and 1.0
+        transform.rotation = Quat::from_rotation_z(rot_info.last_rotation + progress * (rot_info.latest_rotation - rot_info.last_rotation));
     }
 }
\ No newline at end of file
diff --git a/crates/unified/src/client/mod.rs b/crates/unified/src/client/mod.rs
index e6c1afc0e78ffef9f101a5667f456de7d489d3f1..02dfb0f1127e575bfcfde87d002b75bd8c568a38 100644
--- a/crates/unified/src/client/mod.rs
+++ b/crates/unified/src/client/mod.rs
@@ -59,7 +59,7 @@ pub mod starguide;
 pub mod crafting;
 pub mod components;
 pub mod plugins;
-mod interpolation;
+pub mod interpolation;
 
 pub struct ClientPlugin {
     pub server: Option<String>
diff --git a/crates/unified/src/client/parts.rs b/crates/unified/src/client/parts.rs
index e0878d4b27983c90309e430b67a889c07e23b911..de82b98a65de56e1a0e4c41a8ce7ef8749eb0015 100644
--- a/crates/unified/src/client/parts.rs
+++ b/crates/unified/src/client/parts.rs
@@ -11,7 +11,7 @@ use crate::client::components::Me;
 use crate::client::ship::attachment::AttachmentDebugRes;
 use crate::prelude::*;
 use bevy_replicon::client::confirm_history::ConfirmHistory;
-use crate::client::interpolation::TransformInterpolationInfo;
+use crate::client::interpolation::{RotationInterpolationInfo, TranslationInterpolationInfo};
 
 pub fn parts_plugin(app: &mut App) {
     app.insert_resource(DragResource { dragged: None });
@@ -60,11 +60,18 @@ fn handle_incoming_parts(
             .insert(MAIN_LAYER)
             .insert(sprite)
             .insert(Pickable::default())
-            .insert(TransformInterpolationInfo {
+            .insert(TranslationInterpolationInfo {
                 last_dt: Duration::from_millis(50), // assume it was 20tps because we don't know
                 this_tick_start: bevy::platform::time::Instant::now(),
-                latest_transform: transform.clone(),
-                last_transform: transform.clone(),
+                latest_position: transform.translation.truncate(),
+                last_position: transform.translation.truncate(),
+            })
+            .insert(RotationInterpolationInfo {
+                last_dt: Duration::from_millis(50), // assume it was 20tps because we don't know
+                this_tick_start: bevy::platform::time::Instant::now(),
+                last_angular_velocity: 0.0,
+                latest_rotation: transform.rotation.to_euler(EulerRot::XYZ).2,
+                last_rotation: transform.rotation.to_euler(EulerRot::XYZ).2,
             })
             .observe(on_part_click)
             .observe(open_crafting_ui);
diff --git a/crates/unified/src/client/planet/incoming_planets.rs b/crates/unified/src/client/planet/incoming_planets.rs
index 2ffc7f289016934c46deaf755bf28131dc9b5316..0a6e35410436c309477f49442b163d1ec73ea5b0 100644
--- a/crates/unified/src/client/planet/incoming_planets.rs
+++ b/crates/unified/src/client/planet/incoming_planets.rs
@@ -1,7 +1,9 @@
+use std::time::Duration;
 use crate::shared::config::planet::{Planet, SpecialSpriteProperties};
 use crate::prelude::*;
 use crate::shared::ecs::{MAIN_STAR_LAYERS};
 use bevy_replicon::client::confirm_history::ConfirmHistory;
+use crate::client::interpolation::{RotationInterpolationInfo, TranslationInterpolationInfo};
 
 pub fn incoming_planets_plugin(app: &mut App) {
     app.add_systems(Update, (handle_incoming_planets, handle_updated_planets));
@@ -24,7 +26,20 @@ fn handle_incoming_planets(
     for (new_entity, new_planet, transform, confirm_history) in new_planets.iter() {
         commands.entity(new_entity)
             .insert(MAIN_STAR_LAYERS.clone())
-            .insert(build_planet_sprite(new_planet, &asset_server));
+            .insert(build_planet_sprite(new_planet, &asset_server))
+            .insert(TranslationInterpolationInfo {
+                last_dt: Duration::from_millis(50), // assume it was 20tps because we don't know
+                this_tick_start: bevy::platform::time::Instant::now(),
+                latest_position: transform.translation.truncate(),
+                last_position: transform.translation.truncate(),
+            })
+            .insert(RotationInterpolationInfo {
+                last_dt: Duration::from_millis(50), // assume it was 20tps because we don't know
+                this_tick_start: bevy::platform::time::Instant::now(),
+                last_angular_velocity: 0.0,
+                latest_rotation: transform.rotation.to_euler(EulerRot::XYZ).2,
+                last_rotation: transform.rotation.to_euler(EulerRot::XYZ).2,
+            });
         trace!(?new_planet, "prepared new planet");
     }
 }
diff --git a/crates/unified/src/shared/net.rs b/crates/unified/src/shared/net.rs
index 67a1699a166636101ae5332f3e883c65835424b5..3845b629272dbd9021010139de5be0936d7afd9e 100644
--- a/crates/unified/src/shared/net.rs
+++ b/crates/unified/src/shared/net.rs
@@ -17,8 +17,8 @@ pub fn register_replication(app: &mut App) {
     app
         .add_mapped_server_message::<Hi>(Channel::Ordered)
 
-        .replicate::<Transform>()
-        .replicate::<GlobalTransform>()
+        .replicate_once::<Transform>()
+        .replicate_once::<GlobalTransform>()
 
         .replicate::<Position>()
         .replicate::<Rotation>()