unit influence blocks building

OpenRa.Game/UnitInfluenceMap.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace OpenRa.Game
+{
+	class UnitInfluenceMap
+	{
+		Actor[,] influence = new Actor[128, 128];
+
+		/* todo: incremental updates for great justice [and perf] */
+
+		public void Tick()
+		{
+			influence = new Actor[128, 128];
+
+			var units = Game.world.Actors
+				.Select( a => a.traits.GetOrDefault<Traits.Mobile>() ).Where( m => m != null );
+
+			foreach (var u in units)
+				foreach (var c in u.OccupiedCells())
+					influence[c.X, c.Y] = u.self;
+		}
+
+		public Actor GetUnitAt(int2 a) { return influence[a.X, a.Y]; }
+	}
+}