factor out layout policy for ScrollPanelWidget; add GridLayout option.

OpenRA.Game/Widgets/ListLayout.cs

@@ -0,0 +1,28 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2011 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
+
+namespace OpenRA.Widgets
+{
+	public class ListLayout : ILayout
+	{
+		ScrollPanelWidget widget;
+
+		public ListLayout(ScrollPanelWidget w) { widget = w; }
+
+		public void AdjustChild(Widget w)
+		{
+			if (widget.Children.Count == 0)
+				widget.ContentHeight = widget.ItemSpacing;
+
+			w.Bounds.Y += widget.ContentHeight;
+			widget.ContentHeight += w.Bounds.Height + widget.ItemSpacing;
+		}
+	}
+}