From 71ade52ef032a59f7fc96e236eefa00dbc6285d7 Mon Sep 17 00:00:00 2001
From: ghostly_zsh <ghostly@e3t.cc>
Date: Tue, 18 Nov 2025 00:43:11 -0600
Subject: [PATCH] even better animation

---
 crates/unified/src/client/parts.rs | 48 ++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 15 deletions(-)

diff --git a/crates/unified/src/client/parts.rs b/crates/unified/src/client/parts.rs
index 83121184e7d203a0d22e3ae7fbe9c20d185beb34..0a8763f8d09126397632740bb4424f52f497aea9 100644
--- a/crates/unified/src/client/parts.rs
+++ b/crates/unified/src/client/parts.rs
@@ -1,3 +1,5 @@
+use std::f32::consts::PI;
+
 use crate::attachment::{Joint, JointOf, Joints, PartInShip, Peer, SnapOf, SnapOfJoint};
 use crate::client::Me;
 use crate::client::colors::GREEN;
@@ -115,9 +117,11 @@ struct SnapResource(Option<Entity>, Option<Entity>);
 #[derive(Component)]
 struct DragGhost;
 #[derive(Component)]
-struct GhostTarget(pub Quat);
-#[derive(Component)]
-struct GhostVelocity(pub Vec3);
+struct Ghost {
+    pub rot: Quat,
+    pub last_target_pos: Vec3,
+    pub vel: Vec3,
+}
 
 const TRANSLATION_SMOOTH: f32 = 0.3;
 const ROTATION_SMOOTH: f32 = 0.1;
@@ -147,7 +151,11 @@ fn on_part_click(
     }
     let mut s = sprite.0.clone();
     s.color = Color::srgba(0.7, 0.7, 0.7, 1.0);
-    commands.spawn((DragGhost, GhostVelocity(Vec3::ZERO), GhostTarget(sprite.1.rotation), *sprite.1, s));
+    commands.spawn((DragGhost, Ghost {
+        rot: sprite.1.rotation,
+        last_target_pos: sprite.1.translation,
+        vel: Vec3::ZERO,
+    }, *sprite.1, s));
 
     drag.0 = Some(ev.event().event_target());
 }
@@ -191,7 +199,7 @@ fn on_part_release(
 /// This code is super cursed, and it will break at the lightest breeze
 fn update_drag_ghosts(
     ghost: Single<
-        (&mut Transform, &mut GhostVelocity, &mut GhostTarget),
+        (&mut Transform, &mut Ghost),
         (
             With<DragGhost>,
             Without<SnapOf>,
@@ -213,12 +221,12 @@ fn update_drag_ghosts(
 ) {
     const CUTOFF: f32 = 25.0; // px
 
-    let (mut ghost, mut ghost_velocity, mut ghost_target) = ghost.into_inner();
+    let (mut ghost, mut ghost_info) = ghost.into_inner();
     let Some(cursor) = cursor.0 else { return };
 
     let mut best_distance = f32::INFINITY;
     let mut best_target = Transform::from_xyz(cursor.x, cursor.y, 0.0);
-    best_target.rotation = ghost_target.0;
+    best_target.rotation = ghost_info.rot;
     let mut snap = None;
     let mut best_parent_position = None;
     let mut best_snap_position = None;
@@ -345,14 +353,24 @@ fn update_drag_ghosts(
             -180.0_f32.to_radians() * time.delta_secs(),
         ));
     }
-    ghost_target.0 = best_target.rotation;
-    ghost.rotation = ghost.rotation.slerp(ghost_target.0, ROTATION_SMOOTH);
-    let disp = ghost.translation - best_target.translation;
-    const K: f32 = 0.07;
-    const C: f32 = 0.5;
-    let a = (-K*disp - C*ghost_velocity.0)/2.0;
-    ghost.translation += ghost_velocity.0;
-    ghost_velocity.0 += a;
+    ghost_info.rot = best_target.rotation;
+    ghost.rotation = ghost.rotation.slerp(ghost_info.rot, ROTATION_SMOOTH);
+    let target_vel = (best_target.translation - ghost_info.last_target_pos)
+        /time.delta_secs();
+    const F: f32 = 2.0; // frequency (Hz)
+    // 0.0 is undamped, 0.0-1.0 is underdamped, 1.0 is critical, and >1.0 is over
+    const ZETA: f32 = 0.7; // damping
+    const R: f32 = -0.6; // initial response speed
+    const K1: f32 = ZETA/(PI*F);
+    const K2: f32 = 1.0/((2.0*PI*F)*(2.0*PI*F));
+    const K3: f32 = (R*ZETA)/(2.0*PI*F);
+    let a = (best_target.translation - ghost.translation
+        + K3*target_vel - K1*ghost_info.vel)/K2;
+
+    ghost.translation += ghost_info.vel*time.delta_secs();
+    ghost_info.vel += a*time.delta_secs();
+
+    ghost_info.last_target_pos = best_target.translation;
 
     rsnap.0 = snap;
     rsnap.1 = best_self_snap;