cleaning techtree & sidebar; building placement is mostly fixed

OpenRa.Game/PlaceBuilding.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using OpenRa.Game.GameRules;
+
+namespace OpenRa.Game
+{
+	class PlaceBuilding : IOrderGenerator
+	{
+		public readonly Player Owner;
+		public readonly string Name;
+
+		public PlaceBuilding(Player owner, string name)
+		{
+			Owner = owner;
+			Name = name;
+		}
+
+		public IEnumerable<Order> Order(int2 xy)
+		{
+			// todo: check that space is free
+			if (Footprint.Tiles(Name, xy).Any(t => !Game.IsCellBuildable(t, UnitMovementType.Wheel)))
+				yield break;
+
+			yield return new PlaceBuildingOrder(this, xy);
+		}
+
+		public void PrepareOverlay(int2 xy)
+		{
+			Game.worldRenderer.uiOverlay.SetCurrentOverlay(xy, Name);
+		}
+	}
+}