Only render shroud/ore that is in the current viewport

OpenRA.Game/Graphics/Viewport.cs

@@ -158,5 +158,14 @@ namespace OpenRA.Graphics
 			if (localPlayer.Shroud.Disabled) return null;
 			return localPlayer.Shroud.Bounds;
 		}
+		
+		public Rectangle ViewBounds()
+		{
+			int2 boundary = new int2(3,3); // Add a curtain of cells around the viewport to account for rounding errors
+			var origin = new int2((int)(scrollPosition.X/Game.CellSize), (int)(scrollPosition.Y/Game.CellSize));		
+			var tl = ViewToWorld(origin).ToInt2() - boundary;
+			var br = ViewToWorld(origin + new int2(Width, Height)).ToInt2() + boundary;
+			return Rectangle.FromLTRB(tl.X, tl.Y, br.X, br.Y);
+		}
 	}
 }