refactor activity queueing

OpenRA.Game/Actor.cs

@@ -151,16 +151,9 @@ namespace OpenRA
 		public void QueueActivity( IActivity nextActivity )
 		{
 			if( currentActivity == null )
-			{
 				currentActivity = nextActivity;
-				return;
-			}
-			var act = currentActivity;
-			while( act.NextActivity != null )
-			{
-				act = act.NextActivity;
-			}
-			act.NextActivity = nextActivity;
+			else
+				currentActivity.Queue( nextActivity );
 		}
 
 		public void CancelActivity()

OpenRA.Game/Traits/Activities/Drag.cs

@@ -14,7 +14,7 @@ namespace OpenRA.Traits.Activities
 {
 	public class Drag : IActivity
 	{
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 
 		float2 endLocation;
 		float2 startLocation;
@@ -40,5 +40,13 @@ namespace OpenRA.Traits.Activities
 		}
 
 		public void Cancel(Actor self) {	}
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 }

OpenRA.Game/Traits/Activities/Idle.cs

@@ -12,9 +12,17 @@ namespace OpenRA.Traits.Activities
 {
 	class Idle : IActivity
 	{
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 
 		public IActivity Tick(Actor self) { return NextActivity; }
 		public void Cancel(Actor self) {}
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 }

OpenRA.Game/Traits/Activities/Move.cs

@@ -17,7 +17,7 @@ namespace OpenRA.Traits.Activities
 {
 	public class Move : IActivity
 	{
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 
 		int2? destination;
 		int nearEnough;
@@ -164,9 +164,7 @@ namespace OpenRA.Traits.Activities
 				Log.Write("debug", "Turn: #{0} from {1} to {2}",
 					self.ActorID, mobile.Facing, firstFacing);
 
-				return new Turn( firstFacing )
-					{ NextActivity = this }
-					.Tick( self );
+				return Util.SequenceActivities( new Turn( firstFacing ), this ).Tick( self );
 			}
 			else
 			{
@@ -261,6 +259,14 @@ namespace OpenRA.Traits.Activities
 			NextActivity = null;
 		}
 
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
+
 		abstract class MovePart : IActivity
 		{
 			public readonly Move move;
@@ -280,11 +286,14 @@ namespace OpenRA.Traits.Activities
 				this.moveFractionTotal = (int)(( to - from ).Length*3);
 			}
 
-			public IActivity NextActivity { get { return move; } set { move.NextActivity = value; } }
-
 			public void Cancel( Actor self )
 			{
-				NextActivity.Cancel( self );
+				move.Cancel( self );
+			}
+
+			public void Queue( IActivity activity )
+			{
+				move.Queue( activity );
 			}
 
 			public IActivity Tick( Actor self )

OpenRA.Game/Traits/Activities/RemoveSelf.cs

@@ -10,18 +10,13 @@
 
 namespace OpenRA.Traits.Activities
 {
-	public class RemoveSelf : IActivity
+	public class RemoveSelf : CancelableActivity
 	{
-		bool isCanceled;
-		public IActivity NextActivity { get; set; }
-
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 			self.Destroy();
 			return null;
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Game/Traits/Activities/Sell.cs

@@ -12,7 +12,7 @@ namespace OpenRA.Traits.Activities
 {
 	class Sell : IActivity
 	{
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 
 		bool started;
 
@@ -55,5 +55,13 @@ namespace OpenRA.Traits.Activities
 		}
 
 		public void Cancel(Actor self) { /* never gonna give you up.. */ }
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 }

OpenRA.Game/Traits/Activities/Turn.cs

@@ -12,9 +12,8 @@ using System.Linq;
 
 namespace OpenRA.Traits.Activities
 {
-	public class Turn : IActivity
+	public class Turn : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
 		int desiredFacing;
 
 		public Turn( int desiredFacing )
@@ -22,8 +21,9 @@ namespace OpenRA.Traits.Activities
 			this.desiredFacing = desiredFacing;
 		}
 
-		public IActivity Tick( Actor self )
+		public override IActivity Tick( Actor self )
 		{
+			if (IsCanceled) return NextActivity;
 			var facing = self.Trait<IFacing>();
 
 			if( desiredFacing == facing.Facing )
@@ -32,11 +32,5 @@ namespace OpenRA.Traits.Activities
 
 			return this;
 		}
-
-		public void Cancel( Actor self )
-		{
-			desiredFacing = self.Trait<IFacing>().Facing;
-			NextActivity = null;
-		}
 	}
 }

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -170,9 +170,33 @@ namespace OpenRA.Traits
 	
 	public interface IActivity
 	{
-		IActivity NextActivity { get; set; }
 		IActivity Tick(Actor self);
 		void Cancel(Actor self);
+		void Queue(IActivity activity);
+	}
+
+	public abstract class CancelableActivity : IActivity
+	{
+		protected IActivity NextActivity { get; private set; }
+		protected bool IsCanceled { get; private set; }
+
+		public abstract IActivity Tick( Actor self );
+		protected virtual void OnCancel() {}
+
+		public void Cancel( Actor self )
+		{
+			IsCanceled = true;
+			NextActivity = null;
+			OnCancel();
+		}
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 
 	public interface IRenderOverlay { void Render(); }

OpenRA.Game/Traits/Util.cs

@@ -113,7 +113,7 @@ namespace OpenRA.Traits
 		public static IActivity SequenceActivities(params IActivity[] acts)
 		{
 			return acts.Reverse().Aggregate(
-				(next, a) => { a.NextActivity = next; return a; });
+				(next, a) => { a.Queue( next ); return a; });
 		}
 
 		public static Color ArrayToColor(int[] x) { return Color.FromArgb(x[0], x[1], x[2]); }

OpenRA.Mods.RA/Activities/Attack.cs

@@ -15,7 +15,7 @@ using OpenRA.Traits.Activities;
 namespace OpenRA.Mods.RA.Activities
 {
 	/* non-turreted attack */
-	public class Attack : IActivity
+	public class Attack : CancelableActivity
 	{
 		Target Target;
 		int Range;
@@ -26,10 +26,11 @@ namespace OpenRA.Mods.RA.Activities
 			Range = range;
 		}
 
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 
-		public IActivity Tick( Actor self )
+		public override IActivity Tick( Actor self )
 		{
+			if (IsCanceled) return NextActivity;
 			var facing = self.Trait<IFacing>();
 			if (!Target.IsValid)
 				return NextActivity;
@@ -37,7 +38,7 @@ namespace OpenRA.Mods.RA.Activities
 			var targetCell = Util.CellContaining(Target.CenterLocation);
 
 			if ((targetCell - self.Location).LengthSquared >= Range * Range)
-				return new Move( Target, Range ) { NextActivity = this };
+				return Util.SequenceActivities( new Move( Target, Range ), this );
 
 			var desiredFacing = Util.GetFacing((targetCell - self.Location).ToFloat2(), 0);
 			var renderUnit = self.TraitOrDefault<RenderUnit>();
@@ -47,7 +48,7 @@ namespace OpenRA.Mods.RA.Activities
 			if (Util.QuantizeFacing(facing.Facing, numDirs) 
 				!= Util.QuantizeFacing(desiredFacing, numDirs))
 			{
-				return new Turn( desiredFacing ) { NextActivity = this };
+				return Util.SequenceActivities( new Turn( desiredFacing ), this );
 			}
 
 			var attack = self.Trait<AttackBase>();
@@ -55,7 +56,5 @@ namespace OpenRA.Mods.RA.Activities
 			attack.DoAttack(self);
 			return this;
 		}
-
-		public void Cancel(Actor self) { Target = Target.None; }
 	}
 }

OpenRA.Mods.RA/Activities/CallFunc.cs

@@ -24,7 +24,7 @@ namespace OpenRA.Mods.RA.Activities
 		
 		Action a;
 		bool interruptable;
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 
 		public IActivity Tick(Actor self)
 		{
@@ -40,5 +40,13 @@ namespace OpenRA.Mods.RA.Activities
 			a = null;
 			NextActivity = null;
 		}
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 }

OpenRA.Mods.RA/Activities/CaptureBuilding.cs

@@ -12,16 +12,15 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class CaptureBuilding : IActivity
+	class CaptureBuilding : CancelableActivity
 	{
 		Target target;
 
 		public CaptureBuilding(Actor target) { this.target = Target.FromActor(target); }
 
-		public IActivity NextActivity { get; set; }
-
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
+			if (IsCanceled) return NextActivity;
 			if (!target.IsValid) return NextActivity;
 			if ((target.Actor.Location - self.Location).Length > 1)
 				return NextActivity;
@@ -41,7 +40,5 @@ namespace OpenRA.Mods.RA.Activities
 			});
 			return NextActivity;
 		}
-
-		public void Cancel(Actor self) { target = Target.None; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/DeliverOre.cs

@@ -15,7 +15,7 @@ namespace OpenRA.Mods.RA.Activities
 {
 	public class DeliverResources : IActivity
 	{
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 
 		bool isDocking;
 
@@ -32,25 +32,33 @@ namespace OpenRA.Mods.RA.Activities
 				harv.ChooseNewProc(self, null);
 
 			if (harv.LinkedProc == null)	// no procs exist; check again in 1s.
-				return new Wait(25) { NextActivity = this };
+				return Util.SequenceActivities( new Wait(25), this );
 
 			var proc = harv.LinkedProc;
 			
 			if( self.Location != proc.Location + proc.Trait<IAcceptOre>().DeliverOffset )
 			{
-				return new Move(proc.Location + proc.Trait<IAcceptOre>().DeliverOffset, 0) { NextActivity = this };
+				return Util.SequenceActivities( new Move(proc.Location + proc.Trait<IAcceptOre>().DeliverOffset, 0), this );
 			}
 			else if (!isDocking)
 			{
 				isDocking = true;
 				proc.Trait<IAcceptOre>().OnDock(self, this);
 			}
-			return new Wait(10) { NextActivity = this };
+			return Util.SequenceActivities( new Wait(10), this );
 		}
 
 		public void Cancel(Actor self)
 		{
 			// TODO: allow canceling of deliver orders?
 		}
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 }

OpenRA.Mods.RA/Activities/Demolish.cs

@@ -13,15 +13,15 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class Demolish : IActivity
+	class Demolish : CancelableActivity
 	{
 		Target target;
-		public IActivity NextActivity { get; set; }
 
 		public Demolish( Actor target ) { this.target = Target.FromActor(target); }
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
+			if( IsCanceled ) return NextActivity;
 			if (!target.IsValid) return NextActivity;
 			if ((target.Actor.Location - self.Location).Length > 1)
 				return NextActivity;
@@ -31,7 +31,5 @@ namespace OpenRA.Mods.RA.Activities
 				() => { if (target.IsValid) target.Actor.Kill(self); })));
 			return NextActivity;
 		}
-
-		public void Cancel(Actor self) { target = Target.None; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/EnterTransport.cs

@@ -12,10 +12,8 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class EnterTransport : IActivity
+	class EnterTransport : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
-		bool isCanceled;
 		public Actor transport;
 
 		public EnterTransport(Actor self, Actor transport)
@@ -23,9 +21,9 @@ namespace OpenRA.Mods.RA.Activities
 			this.transport = transport;
 		}
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 			if (transport == null || !transport.IsInWorld) return NextActivity;
 
 			var cargo = transport.Trait<Cargo>();
@@ -43,7 +41,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return this;
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/Fly.cs

@@ -14,21 +14,18 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class Fly : IActivity
+	public class Fly : CancelableActivity
 	{
 		public readonly float2 Pos;
-		bool isCanceled;
 
 		public Fly(float2 pos) { Pos = pos; }
 		public Fly(int2 pos) { Pos = Util.CenterOfCell(pos); }
 		
-		public IActivity NextActivity { get; set; }
-		
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
 			var cruiseAltitude = self.Info.Traits.Get<PlaneInfo>().CruiseAltitude;
 
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 
 			var d = Pos - self.CenterLocation;
 			if (d.LengthSquared < 50)		/* close enough */
@@ -46,8 +43,6 @@ namespace OpenRA.Mods.RA.Activities
 			FlyUtil.Fly(self, cruiseAltitude);
 			return this;
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 
 	public static class FlyUtil

OpenRA.Mods.RA/Activities/FlyAttack.cs

@@ -12,15 +12,15 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class FlyAttack : IActivity
+	public class FlyAttack : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
 		Target Target;
 
 		public FlyAttack(Target target) { Target = target; }
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
+			if (IsCanceled) return NextActivity;
 			if (!Target.IsValid)
 				return NextActivity;
 
@@ -33,29 +33,22 @@ namespace OpenRA.Mods.RA.Activities
 				new FlyTimed(50),
 				this);
 		}
-
-		public void Cancel(Actor self) { Target = Target.None; NextActivity = null; }
 	}
 
-	public class FlyCircle : IActivity
+	public class FlyCircle : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
 		int2 Target;
-		bool isCanceled;
 
 		public FlyCircle(int2 target) { Target = target; }
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled)
-				return NextActivity;
+			if( IsCanceled ) return NextActivity;
 
 			return Util.SequenceActivities(
 				new Fly(Util.CenterOfCell(Target)),
 				new FlyTimed(50),
 				this);
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/FlyTimed.cs

@@ -12,27 +12,25 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class FlyTimed : IActivity
+	public class FlyTimed : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
 		int remainingTicks;
 
 		public FlyTimed(int ticks) { remainingTicks = ticks; }
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
+			if( IsCanceled ) return NextActivity;
 			var targetAltitude = self.Info.Traits.Get<PlaneInfo>().CruiseAltitude;
 			if (remainingTicks-- == 0) return NextActivity;
 			FlyUtil.Fly(self, targetAltitude);
 			return this;
 		}
-
-		public void Cancel(Actor self) { remainingTicks = 0; NextActivity = null; }
 	}
 
 	public class FlyOffMap : IActivity
 	{
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 		bool isCanceled;
 		public bool Interruptible = true;
 
@@ -52,6 +50,13 @@ namespace OpenRA.Mods.RA.Activities
 				NextActivity = null;
 			}
 		}
-	}
 
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
+	}
 }

OpenRA.Mods.RA/Activities/Follow.cs

@@ -13,7 +13,7 @@ using OpenRA.Traits.Activities;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class Follow : IActivity
+	public class Follow : CancelableActivity
 	{
 		Target Target;
 		int Range;
@@ -24,24 +24,18 @@ namespace OpenRA.Mods.RA.Activities
 			Range = range;
 		}
 
-		public IActivity NextActivity { get; set; }
-
-		public IActivity Tick( Actor self )
+		public override IActivity Tick( Actor self )
 		{
-			if (!Target.IsValid)
-				return NextActivity;
+			if (IsCanceled) return NextActivity;
+			if (!Target.IsValid) return NextActivity;
 
 			var inRange = ( Util.CellContaining( Target.CenterLocation ) - self.Location ).LengthSquared < Range * Range;
 
-			if( !inRange )
-				return new Move( Target, Range ) { NextActivity = this };
+			if( inRange ) return this;
 
-			return this;
-		}
-
-		public void Cancel(Actor self)
-		{
-			Target = Target.None;
+			var ret = new Move( Target, Range );
+			ret.Queue( this );
+			return ret;
 		}
 	}
 }

OpenRA.Mods.RA/Activities/Harvest.cs

@@ -17,7 +17,7 @@ namespace OpenRA.Mods.RA.Activities
 {
 	public class Harvest : IActivity
 	{
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 		bool isHarvesting = false;
 
 		public IActivity Tick( Actor self )
@@ -29,7 +29,7 @@ namespace OpenRA.Mods.RA.Activities
 			harv.LastHarvestedCell = self.Location;
 
 			if( harv.IsFull )
-				return new DeliverResources { NextActivity = NextActivity };
+				return Util.SequenceActivities( new DeliverResources(), NextActivity );
 
 			if (HarvestThisTile(self))
 				return this;
@@ -74,5 +74,13 @@ namespace OpenRA.Mods.RA.Activities
 		}
 
 		public void Cancel(Actor self) { }
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 }

OpenRA.Mods.RA/Activities/HeliAttack.cs

@@ -14,17 +14,15 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class HeliAttack : IActivity
+	public class HeliAttack : CancelableActivity
 	{
 		Target target;
 		public HeliAttack( Target target ) { this.target = target; }
 
-		public IActivity NextActivity { get; set; }
-
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (!target.IsValid)
-				return NextActivity;
+			if (IsCanceled) return NextActivity;
+			if (!target.IsValid) return NextActivity;
 
 			var limitedAmmo = self.TraitOrDefault<LimitedAmmo>();
 			if (limitedAmmo != null && !limitedAmmo.HasAmmo())
@@ -53,7 +51,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return this;
 		}
-
-		public void Cancel(Actor self) { target = Target.None; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/HeliFly.cs

@@ -14,7 +14,7 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class HeliFly : IActivity
+	class HeliFly : CancelableActivity
 	{
 		public readonly float2 Dest;
 		public HeliFly(float2 dest)
@@ -22,13 +22,9 @@ namespace OpenRA.Mods.RA.Activities
 			Dest = dest;
 		}
 
-		public IActivity NextActivity { get; set; }
-		bool isCanceled;
-		
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled)
-				return NextActivity;
+			if (IsCanceled)	return NextActivity;
 
 			var info = self.Info.Traits.Get<HelicopterInfo>();
 			var aircraft = self.Trait<Aircraft>();
@@ -57,7 +53,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return this;
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/HeliLand.cs

@@ -12,17 +12,15 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class HeliLand : IActivity
+	class HeliLand : CancelableActivity
 	{
 		public HeliLand(bool requireSpace) { this.requireSpace = requireSpace; }
 
 		bool requireSpace;
-		bool isCanceled;
-		public IActivity NextActivity { get; set; }
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 			var aircraft = self.Trait<Aircraft>();
 			if (aircraft.Altitude == 0)
 				return NextActivity;
@@ -33,7 +31,5 @@ namespace OpenRA.Mods.RA.Activities
 			--aircraft.Altitude;
 			return this;
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/HeliReturn.cs

@@ -14,11 +14,8 @@ using OpenRA.Traits.Activities;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class HeliReturn : IActivity
+	public class HeliReturn : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
-		bool isCanceled;
-
 		static Actor ChooseHelipad(Actor self)
 		{
 			var rearmBuildings = self.Info.Traits.Get<HelicopterInfo>().RearmBuildings;
@@ -27,9 +24,9 @@ namespace OpenRA.Mods.RA.Activities
 					!Reservable.IsReserved(a));
 		}
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 			var dest = ChooseHelipad(self);
 
 			var initialFacing = self.Info.Traits.Get<AircraftInfo>().InitialFacing;
@@ -54,7 +51,5 @@ namespace OpenRA.Mods.RA.Activities
 				new Rearm(),
 				NextActivity);
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/IdleAnimation.cs

@@ -25,7 +25,7 @@ namespace OpenRA.Mods.RA.Activities
 			this.delay = delay;
 		}
 
-		public IActivity NextActivity { get; set; }
+		IActivity NextActivity { get; set; }
 
 		bool active = true;
 		public IActivity Tick(Actor self)
@@ -43,5 +43,13 @@ namespace OpenRA.Mods.RA.Activities
 			active = false;
 			NextActivity = null;
 		}
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 }

OpenRA.Mods.RA/Activities/Infiltrate.cs

@@ -12,14 +12,14 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class Infiltrate : IActivity
+	class Infiltrate : CancelableActivity
 	{
 		Actor target;
 		public Infiltrate(Actor target) { this.target = target; }
-		public IActivity NextActivity { get; set; }
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
+			if (IsCanceled) return NextActivity;
 			if (target == null || target.IsDead()) return NextActivity;
 			if (target.Owner == self.Owner) return NextActivity;
 
@@ -30,7 +30,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return NextActivity;
 		}
-
-		public void Cancel(Actor self) { target = null; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/Land.cs

@@ -14,21 +14,18 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class Land : IActivity
+	public class Land : CancelableActivity
 	{
-		bool isCanceled;
 		Target Target;
 
 		public Land(Target t) { Target = t; }
 		
-		public IActivity NextActivity { get; set; }
-
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
 			if (!Target.IsValid)
 				Cancel(self);
 			
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 
 			var d = Target.CenterLocation - self.CenterLocation;
 			if (d.LengthSquared < 50)		/* close enough */
@@ -49,7 +46,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return this;
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/LayMines.cs

@@ -17,14 +17,11 @@ namespace OpenRA.Mods.RA.Activities
 {
 	// assumes you have Minelayer on that unit
 
-	class LayMines : IActivity
+	class LayMines : CancelableActivity
 	{
-		bool canceled = false;
-		public IActivity NextActivity { get; set; }
-
-		public IActivity Tick( Actor self )
+		public override IActivity Tick( Actor self )
 		{
-			if (canceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 
 			var limitedAmmo = self.TraitOrDefault<LimitedAmmo>();
 			if (!limitedAmmo.HasAmmo())
@@ -37,8 +34,11 @@ namespace OpenRA.Mods.RA.Activities
 				if (rearmTarget == null)
 					return new Wait(20);
 
-				return new Move(Util.CellContaining(rearmTarget.CenterLocation), rearmTarget)
-					{ NextActivity = new Rearm() { NextActivity = new Repair(rearmTarget) { NextActivity = this } } };
+				return Util.SequenceActivities(
+					new Move(Util.CellContaining(rearmTarget.CenterLocation), rearmTarget),
+					new Rearm(),
+					new Repair(rearmTarget),
+					this );
 			}
 
 			var ml = self.Trait<Minelayer>();
@@ -46,14 +46,14 @@ namespace OpenRA.Mods.RA.Activities
 				ShouldLayMine(self, self.Location))
 			{
 				LayMine(self);
-				return new Wait(20) { NextActivity = this };	// a little wait after placing each mine, for show
+				return Util.SequenceActivities( new Wait(20), this ); // a little wait after placing each mine, for show
 			}
 
 			for (var n = 0; n < 20; n++)		// dont get stuck forever here
 			{
 				var p = ml.minefield.Random(self.World.SharedRandom);
 				if (ShouldLayMine(self, p))
-					return new Move(p, 0) { NextActivity = this };
+					return Util.SequenceActivities( new Move(p, 0), this );
 			}
 
 			// todo: return somewhere likely to be safe (near fix) so we're not sitting out in the minefield.
@@ -80,7 +80,5 @@ namespace OpenRA.Mods.RA.Activities
 					new OwnerInit( self.Owner ),
 				}));
 		}
-
-		public void Cancel( Actor self ) { canceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/Leap.cs

@@ -14,7 +14,7 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class Leap : IActivity
+	class Leap : CancelableActivity
 	{
 		Target target;
 		float2 initialLocation;
@@ -31,12 +31,10 @@ namespace OpenRA.Mods.RA.Activities
 			Sound.Play("dogg5p.aud", self.CenterLocation);
 		}
 
-		public IActivity NextActivity { get; set; }
-		
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (!target.IsValid)
-				return NextActivity;
+			if (IsCanceled) return NextActivity;
+			if (!target.IsValid) return NextActivity;
 
 			t += (1f / delay);
 
@@ -54,7 +52,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return this;
 		}
-
-		public void Cancel(Actor self) { target = new Target(); NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/Rearm.cs

@@ -14,17 +14,15 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class Rearm : IActivity
+	public class Rearm : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
-		bool isCanceled;
 		int remainingTicks = ticksPerPip;
 
 		const int ticksPerPip = 25 * 2;
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 			var limitedAmmo = self.TraitOrDefault<LimitedAmmo>();
 			if (limitedAmmo == null) return NextActivity;
 
@@ -43,7 +41,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return this;
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/Repair.cs

@@ -14,18 +14,16 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class Repair : IActivity
+	public class Repair : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
-		bool isCanceled;
 		int remainingTicks;
 		Actor host;
 
 		public Repair(Actor host) { this.host = host; }
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 			if (host != null && !host.IsInWorld) return NextActivity;
 			if (remainingTicks == 0)
 			{
@@ -58,7 +56,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return this;
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/RepairBuilding.cs

@@ -12,16 +12,15 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class RepairBuilding : IActivity
+	class RepairBuilding : CancelableActivity
 	{
 		Target target;
 
 		public RepairBuilding(Actor target) { this.target = Target.FromActor(target); }
 
-		public IActivity NextActivity { get; set; }
-
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
+			if (IsCanceled) return NextActivity;
 			if (!target.IsValid) return NextActivity;
 			if ((target.Actor.Location - self.Location).Length > 1)
 				return NextActivity;
@@ -35,7 +34,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return NextActivity;
 		}
-
-		public void Cancel(Actor self) { target = Target.None; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/ReturnToBase.cs

@@ -14,11 +14,8 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class ReturnToBase : IActivity
+	public class ReturnToBase : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
-
-		bool isCanceled;
 		bool isCalculated;
 		Actor dest;
 
@@ -88,9 +85,9 @@ namespace OpenRA.Mods.RA.Activities
 			this.dest = dest;
 		}
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 			if (!isCalculated)
 				Calculate(self);
 
@@ -101,7 +98,5 @@ namespace OpenRA.Mods.RA.Activities
 				new Land(Target.FromActor(dest)),
 				NextActivity);
 		}
-
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/Teleport.cs

@@ -13,10 +13,8 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class Teleport : IActivity
+	public class Teleport : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
-
 		int2 destination;
 
 		public Teleport(int2 destination)
@@ -24,12 +22,10 @@ namespace OpenRA.Mods.RA.Activities
 			this.destination = destination;
 		}
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
 			self.TraitsImplementing<IMove>().FirstOrDefault().SetPosition(self, destination);
 			return NextActivity;
 		}
-
-		public void Cancel(Actor self) { }
 	}
 }

OpenRA.Mods.RA/Activities/Transform.cs

@@ -17,12 +17,11 @@ using OpenRA.FileFormats;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	class Transform : IActivity
+	class Transform : CancelableActivity
 	{
 		string actor = null;
 		int2 offset;
 		string[] sounds = null;		
-		bool isCanceled;
 		int facing;
 		
 		RenderBuilding rb;
@@ -35,9 +34,6 @@ namespace OpenRA.Mods.RA.Activities
 			rb = self.TraitOrDefault<RenderBuilding>();
 		}
 
-		public IActivity NextActivity { get; set; }
-
-		
 		void DoTransform(Actor self)
 		{
 			// Hack: repeat the first frame of the make anim instead
@@ -70,9 +66,9 @@ namespace OpenRA.Mods.RA.Activities
 		}
 		
 		bool started = false;
-		public IActivity Tick( Actor self )
+		public override IActivity Tick( Actor self )
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 			if (started) return this;
 			
 			if (rb == null)
@@ -88,7 +84,5 @@ namespace OpenRA.Mods.RA.Activities
 			}
 			return this;
 		}
-		
-		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 }

OpenRA.Mods.RA/Activities/UnloadCargo.cs

@@ -16,11 +16,8 @@ using System.Drawing;
 
 namespace OpenRA.Mods.RA.Activities
 {
-	public class UnloadCargo : IActivity
+	public class UnloadCargo : CancelableActivity
 	{
-		public IActivity NextActivity { get; set; }
-		bool isCanceled;
-
 		int2? ChooseExitTile(Actor self, Actor cargo)
 		{
 			// is anyone still hogging this tile?
@@ -38,16 +35,16 @@ namespace OpenRA.Mods.RA.Activities
 			return null;
 		}
 
-		public IActivity Tick(Actor self)
+		public override IActivity Tick(Actor self)
 		{
-			if (isCanceled) return NextActivity;
+			if (IsCanceled) return NextActivity;
 
 			// if we're a thing that can turn, turn to the
 			// right facing for the unload animation
 			var facing = self.TraitOrDefault<IFacing>();
 			var unloadFacing = self.Info.Traits.Get<CargoInfo>().UnloadFacing;
 			if (facing != null && facing.Facing != unloadFacing)
-				return new Turn(unloadFacing) { NextActivity = this };
+				return Util.SequenceActivities( new Turn(unloadFacing), this );
 
 			// todo: handle the BS of open/close sequences, which are inconsistent,
 			//		for reasons that probably make good sense to the westwood guys.
@@ -82,7 +79,5 @@ namespace OpenRA.Mods.RA.Activities
 
 			return this;
 		}
-
-		public void Cancel(Actor self) { NextActivity = null; isCanceled = true; }
 	}
 }

OpenRA.Mods.RA/Activities/Wait.cs

@@ -16,6 +16,7 @@ namespace OpenRA.Mods.RA.Activities
 	{
 		int remainingTicks;
 		bool interruptable = true;
+		IActivity NextActivity { get; set; }
 
 		public Wait(int period) { remainingTicks = period; }
 		public Wait(int period, bool interruptable)
@@ -24,7 +25,7 @@ namespace OpenRA.Mods.RA.Activities
 			this.interruptable = interruptable;
 		}
 		
-		public IActivity Tick(Actor self)
+		public virtual IActivity Tick(Actor self)
 		{
 			if (remainingTicks-- == 0) return NextActivity;
 			return this;
@@ -38,6 +39,13 @@ namespace OpenRA.Mods.RA.Activities
 			remainingTicks = 0;
 			NextActivity = null;
 		}
-		public IActivity NextActivity { get; set; }
+
+		public void Queue( IActivity activity )
+		{
+			if( NextActivity != null )
+				NextActivity.Queue( activity );
+			else
+				NextActivity = activity;
+		}
 	}
 }