Distinguish between line build nodes and segments.

OpenRA.Mods.Common/Orders/PlaceBuildingOrderGenerator.cs

@@ -178,7 +178,7 @@ namespace OpenRA.Mods.Common.Orders
 
 				if (!Game.GetModifierKeys().HasModifier(Modifiers.Shift))
 					foreach (var t in BuildingUtils.GetLineBuildCells(world, topLeft, building, buildingInfo))
-						cells.Add(t, buildingInfo.IsCloseEnoughToBase(world, world.LocalPlayer, building, t));
+						cells.Add(t.First, buildingInfo.IsCloseEnoughToBase(world, world.LocalPlayer, building, t.First));
 				else
 					cells.Add(topLeft, buildingInfo.IsCloseEnoughToBase(world, world.LocalPlayer, building, topLeft));
 			}

OpenRA.Mods.Common/Traits/Buildings/BuildingUtils.cs

@@ -11,6 +11,7 @@
 
 using System.Collections.Generic;
 using System.Linq;
+using OpenRA.Primitives;
 
 namespace OpenRA.Mods.Common.Traits
 {
@@ -48,18 +49,20 @@ namespace OpenRA.Mods.Common.Traits
 					world.IsCellBuildable(t, building, toIgnore));
 		}
 
-		public static IEnumerable<CPos> GetLineBuildCells(World world, CPos location, string name, BuildingInfo bi)
+		public static IEnumerable<Pair<CPos, Actor>> GetLineBuildCells(World world, CPos location, string name, BuildingInfo bi)
 		{
 			var lbi = world.Map.Rules.Actors[name].TraitInfo<LineBuildInfo>();
 			var topLeft = location;	// 1x1 assumption!
 
 			if (world.IsCellBuildable(topLeft, bi))
-				yield return topLeft;
+				yield return Pair.New<CPos, Actor>(topLeft, null);
 
 			// Start at place location, search outwards
 			// TODO: First make it work, then make it nice
 			var vecs = new[] { new CVec(1, 0), new CVec(0, 1), new CVec(-1, 0), new CVec(0, -1) };
 			int[] dirs = { 0, 0, 0, 0 };
+			Actor[] connectors = { null, null, null, null };
+
 			for (var d = 0; d < 4; d++)
 			{
 				for (var i = 1; i < lbi.Range; i++)
@@ -72,17 +75,17 @@ namespace OpenRA.Mods.Common.Traits
 						continue; // Cell is empty; continue search
 
 					// Cell contains an actor. Is it the type we want?
-					var hasConnector = world.ActorMap.GetActorsAt(cell)
+					connectors[d] = world.ActorMap.GetActorsAt(cell)
-						.Any(a => a.Info.TraitInfos<LineBuildNodeInfo>()
+						.FirstOrDefault(a => a.Info.TraitInfos<LineBuildNodeInfo>()
 							.Any(info => info.Types.Overlaps(lbi.NodeTypes) && info.Connections.Contains(vecs[d])));
 
-					dirs[d] = hasConnector ? i : -1;
+					dirs[d] = connectors[d] != null ? i : -1;
 				}
 
 				// Place intermediate-line sections
 				if (dirs[d] > 0)
 					for (var i = 1; i < dirs[d]; i++)
-						yield return topLeft + i * vecs[d];
+						yield return Pair.New(topLeft + i * vecs[d], connectors[d]);
 			}
 		}
 	}

OpenRA.Mods.Common/Traits/Buildings/LineBuild.cs

@@ -10,19 +10,91 @@
 #endregion
 
 using System.Collections.Generic;
+using System.Linq;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
 {
+	public class LineBuildParentInit : IActorInit<Actor[]>
+	{
+		[FieldFromYamlKey] public readonly string[] ParentNames = new string[0];
+		readonly Actor[] parents = null;
+
+		public LineBuildParentInit() { }
+		public LineBuildParentInit(Actor[] init) { parents = init; }
+		public Actor[] Value(World world)
+		{
+			if (parents != null)
+				return parents;
+
+			var sma = world.WorldActor.Trait<SpawnMapActors>();
+			return ParentNames.Select(n => sma.Actors[n]).ToArray();
+		}
+	}
+
+	public interface INotifyLineBuildSegmentsChanged
+	{
+		void SegmentAdded(Actor self, Actor segment);
+		void SegmentRemoved(Actor self, Actor segment);
+	}
+
 	[Desc("Place the second actor in line to build more of the same at once (used for walls).")]
-	public class LineBuildInfo : TraitInfo<LineBuild>
+	public class LineBuildInfo : ITraitInfo
 	{
 		[Desc("The maximum allowed length of the line.")]
 		public readonly int Range = 5;
 
 		[Desc("LineBuildNode 'Types' to attach to.")]
 		public readonly HashSet<string> NodeTypes = new HashSet<string> { "wall" };
+
+		[ActorReference(typeof(LineBuildInfo))]
+		[Desc("Actor type for line-built segments (defaults to same actor).")]
+		public readonly string SegmentType = null;
+
+		public object Create(ActorInitializer init) { return new LineBuild(init, this); }
 	}
 
-	public class LineBuild { }
+	public class LineBuild : INotifyAddedToWorld, INotifyRemovedFromWorld, INotifyLineBuildSegmentsChanged
+	{
+		readonly Actor[] parentNodes = new Actor[0];
+		HashSet<Actor> segments;
+
+		public LineBuild(ActorInitializer init, LineBuildInfo info)
+		{
+			if (init.Contains<LineBuildParentInit>())
+				parentNodes = init.Get<LineBuildParentInit>().Value(init.World);
+		}
+
+		void INotifyLineBuildSegmentsChanged.SegmentAdded(Actor self, Actor segment)
+		{
+			if (segments == null)
+				segments = new HashSet<Actor>();
+
+			segments.Add(segment);
+		}
+
+		void INotifyLineBuildSegmentsChanged.SegmentRemoved(Actor self, Actor segment)
+		{
+			if (segments == null)
+				return;
+
+			segments.Remove(segment);
+		}
+
+		void INotifyAddedToWorld.AddedToWorld(Actor self)
+		{
+			foreach (var parent in parentNodes)
+				if (!parent.Disposed)
+					foreach (var n in parent.TraitsImplementing<INotifyLineBuildSegmentsChanged>())
+						n.SegmentAdded(parent, self);
+		}
+
+		void INotifyRemovedFromWorld.RemovedFromWorld(Actor self)
+		{
+			foreach (var parent in parentNodes)
+				if (!parent.Disposed)
+					foreach (var n in parent.TraitsImplementing<INotifyLineBuildSegmentsChanged>())
+						n.SegmentRemoved(parent, self);
+		}
+	}
 }

OpenRA.Mods.Common/Traits/Player/PlaceBuilding.cs

@@ -74,21 +74,34 @@ namespace OpenRA.Mods.Common.Traits
 
 				if (os == "LineBuild")
 				{
-					var playSounds = true;
+					// Build the parent actor first
+					var placed = w.CreateActor(order.TargetString, new TypeDictionary
+					{
+						new LocationInit(order.TargetLocation),
+						new OwnerInit(order.Player),
+						new FactionInit(faction),
+					});
+
+					foreach (var s in buildingInfo.BuildSounds)
+						Game.Sound.PlayToPlayer(SoundType.World, order.Player, s, placed.CenterPosition);
+
+					// Build the connection segments
+					var segmentType = unit.TraitInfo<LineBuildInfo>().SegmentType;
+					if (string.IsNullOrEmpty(segmentType))
+						segmentType = order.TargetString;
+
 					foreach (var t in BuildingUtils.GetLineBuildCells(w, order.TargetLocation, order.TargetString, buildingInfo))
 					{
-						var building = w.CreateActor(order.TargetString, new TypeDictionary
+						if (t.First == order.TargetLocation)
+							continue;
+
+						w.CreateActor(t.First == order.TargetLocation ? order.TargetString : segmentType, new TypeDictionary
 						{
-							new LocationInit(t),
+							new LocationInit(t.First),
 							new OwnerInit(order.Player),
-							new FactionInit(faction)
+							new FactionInit(faction),
+							new LineBuildParentInit(new[] { t.Second, placed })
 						});
-
-						if (playSounds)
-							foreach (var s in buildingInfo.BuildSounds)
-								Game.Sound.PlayToPlayer(SoundType.World, order.Player, s, building.CenterPosition);
-
-						playSounds = false;
 					}
 				}
 				else if (os == "PlacePlug")