Optimize pipe net appearance updating. (#6469)

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.Server/Atmos/Piping/EntitySystems/AtmosPipeNodeAppearanceSystem.cs

@@ -0,0 +1,81 @@
+using Content.Server.NodeContainer;
+using Content.Server.NodeContainer.EntitySystems;
+using Content.Server.NodeContainer.Nodes;
+using Content.Shared.Atmos;
+using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
+using Robust.Shared.Map;
+using System.Collections.Generic;
+
+namespace Content.Server.Atmos.Piping.EntitySystems;
+
+public sealed class AtmosPipeNodeAppearanceSystem : EntitySystem
+{
+    [Dependency] private readonly IMapManager _mapManager = default!;
+
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        // This should probably just be a directed event, but that would require a weird component that exists only to
+        // receive directed events (*cough* *cough* CableVisComponent *cough*).
+        //
+        // Really I want to target any entity with a PipeConnectorVisualizer or a NodeContainerComponent that contains a
+        // pipe-node. But I don't know of nice way of doing that.
+        SubscribeLocalEvent<NodeGroupsRebuilt>(OnNodeUpdate);
+    }
+
+    private void OnNodeUpdate(ref NodeGroupsRebuilt ev)
+    {
+        UpdateAppearance(ev.NodeOwner);
+    }
+
+    private void UpdateAppearance(EntityUid uid, AppearanceComponent? appearance = null, NodeContainerComponent? container = null,
+        TransformComponent? xform = null)
+    {
+        if (!Resolve(uid, ref appearance, ref container, ref xform, false))
+            return;
+
+        if (!_mapManager.TryGetGrid(xform.GridID, out var grid))
+            return;
+
+        // get connected entities
+        var anyPipeNodes = false;
+        HashSet<EntityUid> connected = new();
+        foreach (var node in container.Nodes.Values)
+        {
+            if (node is not PipeNode)
+                continue;
+
+            anyPipeNodes = true;
+
+            foreach (var connectedNode in node.ReachableNodes)
+            {
+                if (connectedNode is PipeNode)
+                    connected.Add(connectedNode.Owner);
+            }
+        }
+
+        if (!anyPipeNodes)
+            return;
+
+        // find the cardinal directions of any connected entities
+        var netConnectedDirections = PipeDirection.None;
+        var tile = grid.TileIndicesFor(xform.Coordinates);
+        foreach (var neighbour in connected)
+        {
+            var otherTile = grid.TileIndicesFor(Transform(neighbour).Coordinates);
+
+            netConnectedDirections |= (otherTile - tile) switch
+            {
+                (0, 1) => PipeDirection.North,
+                (0, -1) => PipeDirection.South,
+                (1, 0) => PipeDirection.East,
+                (-1, 0) => PipeDirection.West,
+                _ => PipeDirection.None
+            };
+        }
+
+        appearance.SetData(PipeVisuals.VisualState, netConnectedDirections);
+    }
+}