Refactor occupied cells visibility checks.

Provide some common extension methods to reduce code duplication, and also use loops instead of LINQ to reduce allocations and provide a minor speedup.

OpenRA.Mods.Common/ShroudExts.cs

@@ -0,0 +1,39 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2015 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. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System.Collections.Generic;
+using OpenRA.Primitives;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common
+{
+	using OccupiedCells = IEnumerable<Pair<CPos, SubCell>>;
+
+	public static class ShroudExts
+	{
+		public static bool AnyExplored(this Shroud shroud, OccupiedCells cells)
+		{
+			foreach (var cell in cells)
+				if (shroud.IsExplored(cell.First))
+					return true;
+
+			return false;
+		}
+
+		public static bool AnyVisible(this Shroud shroud, OccupiedCells cells)
+		{
+			foreach (var cell in cells)
+				if (shroud.IsVisible(cell.First))
+					return true;
+
+			return false;
+		}
+	}
+}