Avoid allocations when generating RadarSignatureCells.

The RadarWidget can supply a reusable buffer to each trait to avoid individual traits having to return new enumerables. Additionally, this allows the two traits to avoid LINQ and further allocations as they can manually enumerate and populate the buffer themselves.

OpenRA.Mods.Common/Traits/Radar/AppearsOnRadar.cs

@@ -30,12 +30,8 @@ namespace OpenRA.Mods.Common.Traits.Radar
 
 	public class AppearsOnRadar : ConditionalTrait<AppearsOnRadarInfo>, IRadarSignature
 	{
-		static readonly IEnumerable<Pair<CPos, Color>> NoCells = Enumerable.Empty<Pair<CPos, Color>>();
 		IRadarColorModifier modifier;
 
-		Color currentColor = Color.Transparent;
-		Func<Pair<CPos, SubCell>, Pair<CPos, Color>> cellToSignature;
-
 		public AppearsOnRadar(AppearsOnRadarInfo info)
 			: base(info) { }
 
@@ -45,27 +41,24 @@ namespace OpenRA.Mods.Common.Traits.Radar
 			modifier = self.TraitsImplementing<IRadarColorModifier>().FirstOrDefault();
 		}
 
-		public IEnumerable<Pair<CPos, Color>> RadarSignatureCells(Actor self)
+		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 NoCells;
+				return;
 
 			var color = Game.Settings.Game.UsePlayerStanceColors ? self.Owner.PlayerStanceColor(self) : self.Owner.Color.RGB;
 			if (modifier != null)
 				color = modifier.RadarColorOverride(self, color);
 
 			if (Info.UseLocation)
-				return new[] { Pair.New(self.Location, color) };
-
-			// PERF: Cache cellToSignature delegate to avoid allocations as color does not change often.
-			if (currentColor != color)
 			{
-				currentColor = color;
+				destinationBuffer.Add(Pair.New(self.Location, color));
-				cellToSignature = c => Pair.New(c.First, color);
+				return;
 			}
 
-			return self.OccupiesSpace.OccupiedCells().Select(cellToSignature);
+			foreach (var cell in self.OccupiesSpace.OccupiedCells())
+				destinationBuffer.Add(Pair.New(cell.First, color));
 		}
 	}
 }

OpenRA.Mods.Common/Traits/World/EditorActorLayer.cs

@@ -272,9 +272,11 @@ namespace OpenRA.Mods.Common.Traits
 			return nodes;
 		}
 
-		public IEnumerable<Pair<CPos, Color>> RadarSignatureCells(Actor self)
+		public void PopulateRadarSignatureCells(Actor self, List<Pair<CPos, Color>> destinationBuffer)
 		{
-			return cellMap.SelectMany(c => c.Value.Select(p => Pair.New(c.Key, p.Owner.Color.RGB)));
+			foreach (var previewsForCell in cellMap)
+				foreach (var preview in previewsForCell.Value)
+					destinationBuffer.Add(Pair.New(previewsForCell.Key, preview.Owner.Color.RGB));
 		}
 	}
 }

OpenRA.Mods.Common/TraitsInterfaces.cs

@@ -354,7 +354,7 @@ namespace OpenRA.Mods.Common.Traits
 
 	public interface IRadarSignature
 	{
-		IEnumerable<Pair<CPos, Color>> RadarSignatureCells(Actor self);
+		void PopulateRadarSignatureCells(Actor self, List<Pair<CPos, Color>> destinationBuffer);
 	}
 
 	public interface IRadarColorModifier { Color RadarColorOverride(Actor self, Color color); }

OpenRA.Mods.Common/Widgets/RadarWidget.cs

@@ -15,6 +15,7 @@ using System.Drawing;
 using System.Linq;
 using OpenRA.Graphics;
 using OpenRA.Mods.Common.Traits;
+using OpenRA.Primitives;
 using OpenRA.Traits;
 using OpenRA.Widgets;
 
@@ -361,6 +362,8 @@ namespace OpenRA.Mods.Common.Widgets
 				var stride = radarSheet.Size.Width;
 				Array.Clear(radarData, 4 * actorSprite.Bounds.Top * stride, 4 * actorSprite.Bounds.Height * stride);
 
+				var cells = new List<Pair<CPos, Color>>();
+
 				unsafe
 				{
 					fixed (byte* colorBytes = &radarData[0])
@@ -372,7 +375,9 @@ namespace OpenRA.Mods.Common.Widgets
 							if (!t.Actor.IsInWorld || world.FogObscures(t.Actor))
 								continue;
 
-							foreach (var cell in t.Trait.RadarSignatureCells(t.Actor))
+							cells.Clear();
+							t.Trait.PopulateRadarSignatureCells(t.Actor, cells);
+							foreach (var cell in cells)
 							{
 								if (!world.Map.Contains(cell.First))
 									continue;