Force Mobile units to return to the ground layer when becoming idle.

OpenRA.Mods.Common/Traits/Mobile.cs

@@ -16,6 +16,7 @@ using System.Linq;
 using OpenRA.Activities;
 using OpenRA.Mods.Common.Activities;
 using OpenRA.Mods.Common.Effects;
+using OpenRA.Mods.Common.Pathfinder;
 using OpenRA.Primitives;
 using OpenRA.Traits;
 
@@ -381,7 +382,7 @@ namespace OpenRA.Mods.Common.Traits
 	}
 
 	public class Mobile : ConditionalTrait<MobileInfo>, INotifyCreated, IIssueOrder, IResolveOrder, IOrderVoice, IPositionable, IMove,
-		IFacing, IDeathActorInitModifier, INotifyAddedToWorld, INotifyRemovedFromWorld, INotifyBlockingMove, IActorPreviewInitModifier
+		IFacing, IDeathActorInitModifier, INotifyAddedToWorld, INotifyRemovedFromWorld, INotifyBlockingMove, IActorPreviewInitModifier, INotifyBecomingIdle
 	{
 		const int AverageTicksBeforePathing = 5;
 		const int SpreadTicksBeforePathing = 5;
@@ -987,5 +988,34 @@ namespace OpenRA.Mods.Common.Traits
 			if (CanEnterCell(self.Location, self, false))
 				init.Add(new HuskSpeedInit(MovementSpeedForCell(self, self.Location)));
 		}
+
+		CPos? ClosestGroundCell()
+		{
+			var above = new CPos(TopLeft.X, TopLeft.Y);
+			if (CanEnterCell(above))
+				return above;
+
+			var pathFinder = self.World.WorldActor.Trait<IPathFinder>();
+			List<CPos> path;
+			using (var search = PathSearch.Search(self.World, Info, self, true,
+					loc => loc.Layer == 0 && CanEnterCell(loc))
+				.FromPoint(self.Location))
+				path = pathFinder.FindPath(search);
+
+			if (path.Count > 0)
+				return path[0];
+
+			return null;
+		}
+
+		void INotifyBecomingIdle.OnBecomingIdle(Actor self)
+		{
+			if (TopLeft.Layer == 0)
+				return;
+
+			var moveTo = ClosestGroundCell();
+			if (moveTo != null)
+				self.QueueActivity(MoveTo(moveTo.Value, 0));
+		}
 	}
 }