Introduce a new type for representing map coordinates.

To resolve the ambiguity introduced when the introduction of isometric maps meant that cell and map coordinates were no longer equivalent, a new type has been introduced so they can each be represented separately.

OpenRA.Game/MPos.cs

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+#region Copyright & License Information
+/*
+ * Copyright 2007-2014 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;
+using System.Drawing;
+
+namespace OpenRA
+{
+	public struct MPos : IEquatable<MPos>
+	{
+		public readonly int U, V;
+
+		public MPos(int u, int v) { U = u; V = v; }
+		public static readonly MPos Zero = new MPos(0, 0);
+
+		public static bool operator ==(MPos me, MPos other) { return me.U == other.U && me.V == other.V; }
+		public static bool operator !=(MPos me, MPos other) { return !(me == other); }
+
+		public override int GetHashCode() { return U.GetHashCode() ^ V.GetHashCode(); }
+
+		public bool Equals(MPos other) { return other == this; }
+		public override bool Equals(object obj) { return obj is MPos && Equals((MPos)obj); }
+
+		public MPos Clamp(Rectangle r)
+		{
+			return new MPos(Math.Min(r.Right, Math.Max(U, r.Left)),
+							Math.Min(r.Bottom, Math.Max(V, r.Top)));
+		}
+
+		public override string ToString() { return U + "," + V; }
+
+		public CPos ToCPos(Map map)
+		{
+			return ToCPos(map.TileShape);
+		}
+
+		public CPos ToCPos(TileShape shape)
+		{
+			if (shape == TileShape.Rectangle)
+				return new CPos(U, V);
+
+			// Convert from rectangular map position to diamond cell position
+			//  - The staggered rows make this fiddly (hint: draw a diagram!)
+			// (a) Consider the relationships:
+			//  - +1u (even -> odd) adds (1, -1) to (x, y)
+			//  - +1v (even -> odd) adds (1, 0) to (x, y)
+			//  - +1v (odd -> even) adds (0, 1) to (x, y)
+			// (b) Therefore:
+			//  - au + 2bv adds (a + b) to (x, y)
+			//  - a correction factor is added if v is odd
+			var offset = (V & 1) == 1 ? 1 : 0;
+			var y = (V - offset) / 2 - U;
+			var x = V - y;
+			return new CPos(x, y);
+		}
+	}
+}