Fix units from transports appearing at load point.

OpenRA.Mods.Common/Activities/RideTransport.cs

@@ -0,0 +1,81 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2019 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using OpenRA.Mods.Common.Traits;
+using OpenRA.Primitives;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Activities
+{
+	class RideTransport : Enter
+	{
+		readonly Passenger passenger;
+
+		Actor enterActor;
+		Cargo enterCargo;
+		Aircraft enterAircraft;
+
+		public RideTransport(Actor self, Target target)
+			: base(self, target, Color.Green)
+		{
+			passenger = self.Trait<Passenger>();
+		}
+
+		protected override bool TryStartEnter(Actor self, Actor targetActor)
+		{
+			enterActor = targetActor;
+			enterCargo = targetActor.TraitOrDefault<Cargo>();
+			enterAircraft = targetActor.TraitOrDefault<Aircraft>();
+
+			// Make sure we can still enter the transport
+			// (but not before, because this may stop the actor in the middle of nowhere)
+			if (enterCargo == null || !passenger.Reserve(self, enterCargo))
+			{
+				Cancel(self, true);
+				return false;
+			}
+
+			if (enterAircraft != null && !enterAircraft.AtLandAltitude)
+				return false;
+
+			return true;
+		}
+
+		protected override void OnEnterComplete(Actor self, Actor targetActor)
+		{
+			self.World.AddFrameEndTask(w =>
+			{
+				// Make sure the target hasn't changed while entering
+				// OnEnterComplete is only called if targetActor is alive
+				if (targetActor != enterActor)
+					return;
+
+				if (!enterCargo.CanLoad(enterActor, self))
+					return;
+
+				enterCargo.Load(enterActor, self);
+				w.Remove(self);
+			});
+		}
+
+		protected override void OnLastRun(Actor self)
+		{
+			passenger.Unreserve(self);
+		}
+
+		public override void Cancel(Actor self, bool keepQueue = false)
+		{
+			passenger.Unreserve(self);
+
+			base.Cancel(self, keepQueue);
+		}
+	}
+}