Overhaul target line rendering:

- Targets are now defined by the activities
- Queued activities are shown
- Support custom attack colors

OpenRA.Game/Activities/Activity.cs

@@ -12,12 +12,27 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using OpenRA.Primitives;
 using OpenRA.Traits;
 
 namespace OpenRA.Activities
 {
 	public enum ActivityState { Queued, Active, Canceling, Done }
 
+	public class TargetLineNode
+	{
+		public readonly Target Target;
+		public readonly Color Color;
+
+		public TargetLineNode(Target target, Color color)
+		{
+			// Note: Not all activities are drawable. In that case, pass Target.Invalid as target,
+			// if "yield break" in TargetLineNode(Actor self) is not feasible.
+			Target = target;
+			Color = color;
+		}
+	}
+
 	/*
 	 * Things to be aware of when writing activities:
 	 *
@@ -204,6 +219,11 @@ namespace OpenRA.Activities
 			yield break;
 		}
 
+		public virtual IEnumerable<TargetLineNode> TargetLineNodes(Actor self)
+		{
+			yield break;
+		}
+
 		public IEnumerable<string> DebugLabelComponents()
 		{
 			var act = this;