From a21b4f99045f8cc466ebe7be645f3ab251510349 Mon Sep 17 00:00:00 2001
From: ghostly_zsh <ghostly@e3t.cc>
Date: Fri, 17 Apr 2026 17:38:07 -0500
Subject: [PATCH] fix: joint damping now applies specifically parallel to the
 joint

---
 crates/unified/assets/config/world.wc.toml |  6 +-
 crates/unified/src/config/world.rs         |  5 +-
 crates/unified/src/server/damping.rs       | 76 ++++++++++++++++++++++
 crates/unified/src/server/mod.rs           |  7 +-
 crates/unified/src/server/player.rs        | 16 +++--
 5 files changed, 98 insertions(+), 12 deletions(-)
 create mode 100644 crates/unified/src/server/damping.rs

diff --git a/crates/unified/assets/config/world.wc.toml b/crates/unified/assets/config/world.wc.toml
index b2af455d041fdf631e1dfee293c8e654a023e2d9..de0ba2e46a820c8a53d193237f6f97eee885f96e 100644
--- a/crates/unified/assets/config/world.wc.toml
+++ b/crates/unified/assets/config/world.wc.toml
@@ -8,10 +8,10 @@ spawn_parts_interval_secs = 1
 default_height = 50
 default_width = 50
 default_mass = 100
-joint_align_compliance = 0.00002
+joint_point_compliance = 0.00002
 joint_angle_compliance = 0.000000002
-joint_limit_compliance = 0.0006
-joint_linear_damping = 4.0
+joint_distance_damping = 360.0
+#joint_linear_damping = 0.0
 joint_angular_damping = 2.0
 
 [hearty]
diff --git a/crates/unified/src/config/world.rs b/crates/unified/src/config/world.rs
index a534e90d7549066b08dab88e3f368ca5d3aa6a0e..e890089832df793d47639d443c18e4f5865f9ba5 100644
--- a/crates/unified/src/config/world.rs
+++ b/crates/unified/src/config/world.rs
@@ -22,10 +22,9 @@ pub struct WPartConfig {
     pub default_width: f32,
     pub default_height: f32,
     pub default_mass: f32,
-    pub joint_align_compliance: f32,
+    pub joint_point_compliance: f32,
     pub joint_angle_compliance: f32,
-    pub joint_limit_compliance: f32,
-    pub joint_linear_damping: f32,
+    pub joint_distance_damping: f32,
     pub joint_angular_damping: f32,
 }
 
diff --git a/crates/unified/src/server/damping.rs b/crates/unified/src/server/damping.rs
new file mode 100644
index 0000000000000000000000000000000000000000..d94f12314d7153bef5f1cfcb276448f0c288420d
--- /dev/null
+++ b/crates/unified/src/server/damping.rs
@@ -0,0 +1,76 @@
+use avian2d::{dynamics::{joints::EntityConstraint, solver::{joint_damping, schedule::SubstepSolverSystems, solver_body::{SolverBody, SolverBodyInertia}}}, math::RecipOrZero};
+
+use crate::prelude::*;
+
+pub fn damping_plugin(app: &mut App) {
+    let substeps = app.get_schedule_mut(SubstepSchedule).expect("Add SubstepSchedule first");
+    substeps.add_systems(
+        module_joint_damping::<FixedJoint>
+        .after(joint_damping::<DistanceJoint>) // DistanceJoint is the last damping in vanilla avian
+        .in_set(SubstepSolverSystems::Damping)
+    );
+}
+
+#[derive(Component, Debug, Clone, Copy)]
+pub struct ModuleJointDamping {
+    pub distance: f32,
+    pub angular: f32,
+}
+fn module_joint_damping<T: Component + EntityConstraint<2>>(
+    bodies: Query<(&mut SolverBody, &SolverBodyInertia, &Transform)>,
+    joints: Query<(&T, &ModuleJointDamping)>,
+    time: Res<Time>,
+) {
+    let delta_secs = time.delta_secs();
+
+    let mut dummy_body1 = SolverBody::DUMMY;
+    let mut dummy_body2 = SolverBody::DUMMY;
+
+    for (joint, damping) in &joints {
+        let entities = joint.entities();
+
+        let (mut body1, mut inertia1, mut transform1) = (&mut dummy_body1, &SolverBodyInertia::DUMMY, Transform::default());
+        let (mut body2, mut inertia2, mut transform2) = (&mut dummy_body2, &SolverBodyInertia::DUMMY, Transform::default());
+
+        // Get the solver bodies for the two jointed entities.
+        if let Ok((body, inertia, transform)) = unsafe { bodies.get_unchecked(entities[0]) } {
+            body1 = body.into_inner();
+            inertia1 = inertia;
+            transform1 = *transform;
+        }
+        if let Ok((body, inertia, transform)) = unsafe { bodies.get_unchecked(entities[1]) } {
+            body2 = body.into_inner();
+            inertia2 = inertia;
+            transform2 = *transform;
+        }
+
+        let delta_omega = (body2.angular_velocity - body1.angular_velocity)
+            * (damping.angular * delta_secs).min(1.0);
+
+        if !body1.flags.is_kinematic() {
+            body1.angular_velocity += delta_omega;
+        }
+        if !body2.flags.is_kinematic() {
+            body2.angular_velocity -= delta_omega;
+        }
+
+        let position1 = transform1.translation.truncate() + body1.delta_position;
+        let position2 = transform2.translation.truncate() + body2.delta_position;
+
+        let relative_position = position1 - position2;
+
+        let parallel_velocity1 = body1.linear_velocity.project_onto(relative_position.normalize());
+        let parallel_velocity2 = body2.linear_velocity.project_onto(relative_position.normalize());
+        
+        let delta_v = (parallel_velocity2 - parallel_velocity1)
+            * (damping.distance * delta_secs).min(1.0);
+
+        let w1 = inertia1.effective_inv_mass();
+        let w2 = inertia2.effective_inv_mass();
+
+        let p = delta_v * (w1 + w2).recip_or_zero();
+
+        body1.linear_velocity += p * w1;
+        body2.linear_velocity -= p * w2;
+    }
+}
diff --git a/crates/unified/src/server/mod.rs b/crates/unified/src/server/mod.rs
index ea4fa25c38faceb507212c7cd179e62cc2d9892f..d5a2ebdea4e4ce88913981407eb2d1383df957ab 100644
--- a/crates/unified/src/server/mod.rs
+++ b/crates/unified/src/server/mod.rs
@@ -4,11 +4,13 @@ mod part;
 mod heat;
 mod drill;
 mod craft;
+mod damping;
 pub mod planets;
 pub mod player;
 mod system_sets;
 
 use crate::server::craft::craft_plugin;
+use crate::server::damping::damping_plugin;
 use crate::server::drill::drill_plugin;
 use crate::server::earth_parts::spawn_parts_plugin;
 use crate::server::gravity::newtonian_gravity_plugin;
@@ -56,11 +58,12 @@ impl Plugin for ServerPlugin {
         .add_plugins(spawn_parts_plugin)
         .add_plugins(part_management_plugin)
         .add_plugins(server_thrust_plugin)
-        .add_plugins(heat_cooling_plugin)
+        /*.add_plugins(heat_cooling_plugin)
         .add_plugins(heat_radiation_plugin)
-        .add_plugins(heat_conduction_plugin)
+        .add_plugins(heat_conduction_plugin)*/
         .add_plugins(drill_plugin)
         .add_plugins(craft_plugin)
+        .add_plugins(damping_plugin)
         .configure_sets(Update, WorldUpdateSet.before(PlayerInputSet));
         //.configure_sets(Update, PlayerInputSet.before(PhysicsSet::SyncBackend));
     }
diff --git a/crates/unified/src/server/player.rs b/crates/unified/src/server/player.rs
index 9e67222dbe76ce06a6ae14be483f8ab0ab796d09..8d069030f5f0358d0f9c63fa86303b421aa1f8b7 100644
--- a/crates/unified/src/server/player.rs
+++ b/crates/unified/src/server/player.rs
@@ -3,6 +3,7 @@ pub mod thrust;
 
 use crate::attachment::{Joint, JointOf, Joints, PartInShip, Peer, SnapOf, SnapOfJoint};
 use crate::ecs::{DragRequestEvent, Part, Player, PlayerStorage};
+use crate::server::damping::ModuleJointDamping;
 use crate::server::system_sets::PlayerInputSet;
 use crate::server::ConnectedNetworkEntity;
 use crate::prelude::*;
@@ -22,6 +23,7 @@ pub fn player_management_plugin(app: &mut App) {
             .in_set(PlayerInputSet),
     );
     app.add_systems(Update, complete_partial_disconnects);
+    app.add_systems(FixedUpdate, complete_partial_disconnects);
 }
 
 #[derive(Component)]
@@ -349,7 +351,7 @@ fn dragging(
             );
 
             // create the joint...
-            let joint = PrismaticJoint::new(target_part.2, source_part.2)
+            /*let joint = PrismaticJoint::new(target_part.2, source_part.2)
                 .with_slider_axis(source_joint.2.translation.xy().normalize())
                 .with_local_anchor1(target_joint.2.translation.xy())
                 .with_local_basis1(target_joint.0.transform.rotation.to_euler(EulerRot::ZYX).0 + PI
@@ -357,9 +359,15 @@ fn dragging(
                 .with_limits(0.0, 0.0)
                 .with_align_compliance(world_config.part.joint_align_compliance)
                 .with_angle_compliance(world_config.part.joint_angle_compliance)
-                .with_limit_compliance(world_config.part.joint_limit_compliance);
-            let joint_damping = JointDamping {
-                linear: world_config.part.joint_linear_damping,
+                .with_limit_compliance(world_config.part.joint_limit_compliance);*/
+            let joint = FixedJoint::new(target_part.2, source_part.2)
+                .with_local_anchor1(target_joint.2.translation.xy())
+                .with_local_basis1(target_joint.0.transform.rotation.to_euler(EulerRot::ZYX).0 + PI
+                    - source_joint.0.transform.rotation.to_euler(EulerRot::ZYX).0)
+                .with_point_compliance(world_config.part.joint_point_compliance)
+                .with_angle_compliance(world_config.part.joint_angle_compliance);
+            let joint_damping = ModuleJointDamping {
+                distance: world_config.part.joint_distance_damping,
                 angular: world_config.part.joint_angular_damping,
             };