support transforming to a different actor type as a result of a passenger entering or leaving

OpenRA.Mods.RA/OpenRA.Mods.RA.csproj

@@ -324,6 +324,7 @@
     <Compile Include="ThrowsParticle.cs" />
     <Compile Include="TraitsInterfaces.cs" />
     <Compile Include="TransformOnCapture.cs" />
+    <Compile Include="TransformOnPassenger.cs" />
     <Compile Include="Transforms.cs" />
     <Compile Include="Turreted.cs" />
     <Compile Include="Valued.cs" />

OpenRA.Mods.RA/TransformOnPassenger.cs

@@ -0,0 +1,48 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2011 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. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System.Linq;
+using OpenRA.FileFormats;
+using OpenRA.Mods.RA.Buildings;
+using OpenRA.Mods.RA.Render;
+using OpenRA.Mods.RA.Activities;
+using OpenRA.Traits;
+using OpenRA.Traits.Activities;
+
+namespace OpenRA.Mods.RA
+{
+	public class TransformOnPassengerInfo : ITraitInfo
+	{
+		[ActorReference] public readonly string[] PassengerTypes = {};
+		[ActorReference] public readonly string OnEnter = null;
+		[ActorReference] public readonly string OnExit = null;
+
+		public object Create(ActorInitializer init) { return new TransformOnPassenger(this); }
+	}
+
+	public class TransformOnPassenger : INotifyPassengerEntered, INotifyPassengerExited
+	{
+		TransformOnPassengerInfo info;
+
+		public TransformOnPassenger(TransformOnPassengerInfo info) { this.info = info; }
+
+		void MaybeTransform(Actor self, Actor passenger, string transformTo)
+		{
+			if (info.PassengerTypes.Contains(passenger.Info.Name) && transformTo != null)
+			{
+				self.CancelActivity();
+				self.QueueActivity( new Transform(self, transformTo) { Facing = self.Trait<IFacing>().Facing } );
+			}
+		}
+
+		public void PassengerEntered(Actor self, Actor passenger) { MaybeTransform(self, passenger, info.OnEnter); }
+		public void PassengerExited(Actor self, Actor passenger) { MaybeTransform(self, passenger, info.OnExit); }
+	}
+}