Implement heightmap-aware view -> cell conversion.

OpenRA.Game/Exts.cs

@@ -87,6 +87,29 @@ namespace OpenRA
 			return r.Contains(p.ToPointF());
 		}
 
+		static int WindingDirectionTest(int2 v0, int2 v1, int2 p)
+		{
+			return (v1.X - v0.X) * (p.Y - v0.Y) - (p.X - v0.X) * (v1.Y - v0.Y);
+		}
+
+		public static bool PolygonContains(this int2[] polygon, int2 p)
+		{
+			var windingNumber = 0;
+
+			for (var i = 0; i < polygon.Length; i++)
+			{
+				var tv = polygon[i];
+				var nv = polygon[(i + 1) % polygon.Length];
+
+				if (tv.Y <= p.Y && nv.Y > p.Y && WindingDirectionTest(tv, nv, p) > 0)
+					windingNumber++;
+				else if (tv.Y > p.Y && nv.Y <= p.Y && WindingDirectionTest(tv, nv, p) < 0)
+					windingNumber--;
+			}
+
+			return windingNumber != 0;
+		}
+
 		public static bool HasModifier(this Modifiers k, Modifiers mod)
 		{
 			return (k & mod) == mod;