From dc538d5f9aeb7635278cf40d12df489ef59419a2 Mon Sep 17 00:00:00 2001
From: ghostly_zsh <ghostly@e3t.cc>
Date: Mon, 17 Nov 2025 23:39:55 -0600
Subject: [PATCH] feat: spring-like ghost tracking

---
 crates/unified/src/client/parts.rs | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/crates/unified/src/client/parts.rs b/crates/unified/src/client/parts.rs
index 1d1d3a7fe5c7a8299b93277c67b132589434f51b..83121184e7d203a0d22e3ae7fbe9c20d185beb34 100644
--- a/crates/unified/src/client/parts.rs
+++ b/crates/unified/src/client/parts.rs
@@ -116,6 +116,8 @@ struct SnapResource(Option<Entity>, Option<Entity>);
 struct DragGhost;
 #[derive(Component)]
 struct GhostTarget(pub Quat);
+#[derive(Component)]
+struct GhostVelocity(pub Vec3);
 
 const TRANSLATION_SMOOTH: f32 = 0.3;
 const ROTATION_SMOOTH: f32 = 0.1;
@@ -145,7 +147,7 @@ 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, GhostTarget(sprite.1.rotation), *sprite.1, s));
+    commands.spawn((DragGhost, GhostVelocity(Vec3::ZERO), GhostTarget(sprite.1.rotation), *sprite.1, s));
 
     drag.0 = Some(ev.event().event_target());
 }
@@ -189,7 +191,7 @@ 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 GhostTarget),
+        (&mut Transform, &mut GhostVelocity, &mut GhostTarget),
         (
             With<DragGhost>,
             Without<SnapOf>,
@@ -211,7 +213,7 @@ fn update_drag_ghosts(
 ) {
     const CUTOFF: f32 = 25.0; // px
 
-    let (mut ghost, mut ghost_target) = ghost.into_inner();
+    let (mut ghost, mut ghost_velocity, mut ghost_target) = ghost.into_inner();
     let Some(cursor) = cursor.0 else { return };
 
     let mut best_distance = f32::INFINITY;
@@ -345,8 +347,12 @@ fn update_drag_ghosts(
     }
     ghost_target.0 = best_target.rotation;
     ghost.rotation = ghost.rotation.slerp(ghost_target.0, ROTATION_SMOOTH);
-    let dx = TRANSLATION_SMOOTH * (best_target.translation - ghost.translation);
-    ghost.translation += dx;
+    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;
 
     rsnap.0 = snap;
     rsnap.1 = best_self_snap;