Fix center of mass mispredict when placing tiles (#37969)

fix COM mispredict

Content.Shared/Shuttles/Systems/SharedShuttleSystem.cs

@@ -8,6 +8,7 @@ using Robust.Shared.Map.Components;
 using Robust.Shared.Physics;
 using Robust.Shared.Physics.Collision.Shapes;
 using Robust.Shared.Physics.Components;
+using Robust.Shared.Physics.Systems;
 
 namespace Content.Shared.Shuttles.Systems;
 
@@ -15,12 +16,15 @@ public abstract partial class SharedShuttleSystem : EntitySystem
 {
     [Dependency] private readonly IMapManager _mapManager = default!;
     [Dependency] private readonly ItemSlotsSystem _itemSlots = default!;
+    [Dependency] protected readonly FixtureSystem Fixtures = default!;
     [Dependency] protected readonly SharedMapSystem Maps = default!;
+    [Dependency] protected readonly SharedPhysicsSystem Physics = default!;
     [Dependency] protected readonly SharedTransformSystem XformSystem = default!;
     [Dependency] private readonly EntityWhitelistSystem _whitelistSystem = default!;
 
     public const float FTLRange = 256f;
     public const float FTLBufferRange = 8f;
+    public const float TileDensityMultiplier = 0.5f;
 
     private EntityQuery<MapGridComponent> _gridQuery;
     private EntityQuery<PhysicsComponent> _physicsQuery;
@@ -31,11 +35,23 @@ public abstract partial class SharedShuttleSystem : EntitySystem
     public override void Initialize()
     {
         base.Initialize();
+
+        SubscribeLocalEvent<FixturesComponent, GridFixtureChangeEvent>(OnGridFixtureChange);
+
         _gridQuery = GetEntityQuery<MapGridComponent>();
         _physicsQuery = GetEntityQuery<PhysicsComponent>();
         _xformQuery = GetEntityQuery<TransformComponent>();
     }
 
+    private void OnGridFixtureChange(EntityUid uid, FixturesComponent manager, GridFixtureChangeEvent args)
+    {
+        foreach (var fixture in args.NewFixtures)
+        {
+            Physics.SetDensity(uid, fixture.Key, fixture.Value, TileDensityMultiplier, false, manager);
+            Fixtures.SetRestitution(uid, fixture.Key, fixture.Value, 0.1f, false, manager);
+        }
+    }
+
     /// <summary>
     /// Returns whether an entity can FTL to the specified map.
     /// </summary>