Add a ProjectedCellLayer and use it in Shroud.cs

OpenRA.Game/Map/ProjectedCellLayer.cs

@@ -0,0 +1,50 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2020 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 OpenRA.Primitives;
+
+namespace OpenRA
+{
+	public sealed class ProjectedCellLayer<T> : CellLayerBase<T>
+	{
+		public ProjectedCellLayer(Map map)
+			: base(map) { }
+
+		public ProjectedCellLayer(MapGridType gridType, Size size)
+			: base(gridType, size) { }
+
+		// Resolve an array index from map coordinates.
+		int Index(PPos uv)
+		{
+			return uv.V * Size.Width + uv.U;
+		}
+
+		/// <summary>Gets or sets the layer contents using projected map coordinates.</summary>
+		public T this[PPos uv]
+		{
+			get
+			{
+				return entries[Index(uv)];
+			}
+
+			set
+			{
+				entries[Index(uv)] = value;
+			}
+		}
+
+		public bool Contains(PPos uv)
+		{
+			return bounds.Contains(uv.U, uv.V);
+		}
+	}
+}