Moony z level hack (#15031)

* save work

* Adds Z levels

* a

* ladders + parallax scroll

* zoom out not in

* oops, sandbox

* oops i broke the law

* run ci

* fuck

---------

Co-authored-by: moonheart08 <moonheart08@users.noreply.github.com>

Content.Server/zlevels/ThirdDimension/LadderSystem.cs

@@ -0,0 +1,56 @@
+using Content.Shared._Afterlight.ThirdDimension;
+using Content.Shared.Interaction;
+using Robust.Server.GameObjects;
+using Robust.Shared.Map;
+
+namespace Content.Server._Afterlight.ThirdDimension;
+
+/// <summary>
+/// This handles...
+/// </summary>
+public sealed class LadderSystem : EntitySystem
+{
+    [Dependency] private readonly SharedZLevelSystem _zLevel = default!;
+    [Dependency] private readonly TransformSystem _transform = default!;
+
+    /// <inheritdoc/>
+    public override void Initialize()
+    {
+        SubscribeLocalEvent<LadderComponent, InteractHandEvent>(OnInteractHand);
+    }
+
+    public override void Update(float frameTime)
+    {
+        var query = EntityQueryEnumerator<LadderComponent, TransformComponent>();
+
+        while (query.MoveNext(out _, out var ladder, out var xform))
+        {
+            if (!ladder.Primary || Deleted(ladder.OtherHalf))
+                return;
+
+            // Track it, it "hangs" from above.
+            _transform.SetWorldPosition(ladder.OtherHalf.Value, _transform.GetWorldPosition(xform));
+        }
+    }
+
+    private void OnInteractHand(EntityUid uid, LadderComponent component, InteractHandEvent args)
+    {
+        EnsureOpposing(uid, component);
+        _zLevel.TryTraverse(!component.Primary, args.User);
+    }
+
+    private void EnsureOpposing(EntityUid uid, LadderComponent ladder)
+    {
+        if (!ladder.Primary || !Deleted(ladder.OtherHalf))
+            return;
+
+        var parentXform = Transform(uid);
+        var maybeBelow = _zLevel.MapBelow[(int) parentXform.MapID];
+
+        if (maybeBelow is not {} below)
+            return;
+
+        var newCoords = new MapCoordinates(_transform.GetWorldPosition(parentXform), below);
+        ladder.OtherHalf = Spawn(ladder.OtherHalfProto, newCoords);
+    }
+}