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/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;