Snapline for middle of Object (like in VisualStudio)

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

@@ -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)