Add RadarIcon trait

To make something like the + shown for heros on the original game

OpenRA.Mods.Gen/OpenRA.Mods.Gen.csproj

@@ -104,6 +104,7 @@
     <Compile Include="Traits\Conditions\GrantConditionOnProduction.cs" />
     <Compile Include="Traits\Conditions\HordeBonus.cs" />
     <Compile Include="Traits\Conditions\GrantHordeBonus.cs" />
+    <Compile Include="Traits\Radar\RadarIcon.cs" />
     <Compile Include="Traits\Render\WithSupplyCollectionOverlay.cs" />
     <Compile Include="Traits\Render\WithSupplyDeliveryOverlay.cs" />
     <Compile Include="Traits\TransformOnCondition.cs" />

OpenRA.Mods.Gen/Traits/Radar/RadarIcon.cs

@@ -0,0 +1,71 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2018 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 System;
+using System.Collections.Generic;
+using System.Drawing;
+using System.Linq;
+using OpenRA.Primitives;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Traits.Radar
+{
+	public class RadarIconInfo : ConditionalTraitInfo
+	{
+		public readonly HashSet<CVec> Locations = new HashSet<CVec>
+		{
+			new CVec(-1, 0),
+			new CVec(-2, 0),
+			new CVec(1, 0),
+			new CVec(2, 0),
+			new CVec(0, -1),
+			new CVec(0, -2),
+			new CVec(0, 1),
+			new CVec(0, 2)
+		};
+
+		public readonly Color Color = Color.White;
+
+		[Desc("Player stances who can view this actor's icon on radar.")]
+		public readonly Stance ValidStances = Stance.Ally;
+
+		public override object Create(ActorInitializer init) { return new RadarIcon(this); }
+	}
+
+	public class RadarIcon : ConditionalTrait<RadarIconInfo>, IRadarSignature
+	{
+		IRadarColorModifier modifier;
+
+		public RadarIcon(RadarIconInfo info)
+			: base(info) { }
+
+		protected override void Created(Actor self)
+		{
+			base.Created(self);
+			modifier = self.TraitsImplementing<IRadarColorModifier>().FirstOrDefault();
+		}
+
+		public void PopulateRadarSignatureCells(Actor self, List<Pair<CPos, Color>> destinationBuffer)
+		{
+			var viewer = self.World.RenderPlayer ?? self.World.LocalPlayer;
+			if (IsTraitDisabled || (viewer != null && !Info.ValidStances.HasStance(self.Owner.Stances[viewer])))
+				return;
+
+			var color = Info.Color;
+			if (modifier != null)
+				color = modifier.RadarColorOverride(self, color);
+
+			var cells = Info.Locations.Select(loc => self.Location + loc);
+			foreach (var cell in cells)
+				destinationBuffer.Add(Pair.New(cell, color));
+		}
+	}
+}