Snapline for middle of Object (like in VisualStudio)

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/Extensions/SnaplinePlacementBehavior.cs

@@ -189,7 +189,7 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 			AddLines(containerRect, 0, false);
 			
 			foreach (var item in ExtendedItem.ContentProperty.CollectionElements
-			         .Except(operation.PlacedItems.Select(f => f.Item)))
+				.Except(operation.PlacedItems.Select(f => f.Item)))
 			{
 				var bounds = GetPosition(operation, item);
 				
@@ -217,6 +217,12 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 				v.Add(new Snapline() { RequireOverlap = requireOverlap, Offset = r2.Left - 1, Start = r.Top, End = r.Bottom });
 			if (filter == null || filter.Value.Horizontal == HorizontalAlignment.Right)
 				v.Add(new Snapline() { RequireOverlap = requireOverlap, Offset = r2.Right - 1, Start = r.Top, End = r.Bottom });
+			
+			if (filter == null)
+			{
+				h.Add(new Snapline() { RequireOverlap = requireOverlap, Offset = r2.Top + Math.Abs((r2.Top - r2.Bottom) / 2), Start = r.Left, End = r.Right });
+				v.Add(new Snapline() { RequireOverlap = requireOverlap, Offset = r2.Left + Math.Abs((r2.Left - r2.Right) / 2), Start = r.Top, End = r.Bottom });
+			}
 		}
 		
 		void AddBaseline(DesignItem item, Rect bounds, List<Snapline> list)
@@ -279,7 +285,7 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 		}
 		
 		static bool Snap(List<Snapline> input, List<Snapline> map, double accuracy,
-		                 out List<Snapline> drawLines, out double delta)
+			out List<Snapline> drawLines, out double delta)
 		{
 			delta = double.MaxValue;
 			drawLines = null;
@@ -288,7 +294,7 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 				foreach (var mapLine in map) {
 					if (Math.Abs(mapLine.Offset - inputLine.Offset) <= accuracy) {
 						if (!inputLine.RequireOverlap && !mapLine.RequireOverlap ||
-						    Math.Max(inputLine.Start, mapLine.Start) < Math.Min(inputLine.End, mapLine.End))
+							Math.Max(inputLine.Start, mapLine.Start) < Math.Min(inputLine.End, mapLine.End))
 						{
 							if (mapLine.Group == inputLine.Group)
 								delta = mapLine.Offset - inputLine.Offset;