Make popup appear in right place.

Perspex.Controls.UnitTests/ControlTests.cs

@@ -92,6 +92,11 @@ namespace Perspex.Controls.UnitTests
             {
                 get { throw new NotImplementedException(); }
             }
+
+            public Point TranslatePointToScreen(Point p)
+            {
+                throw new NotImplementedException();
+            }
         }
     }
 }

Perspex.Controls.UnitTests/TestRoot.cs

@@ -33,5 +33,10 @@ namespace Perspex.Controls.UnitTests
         {
             get { throw new NotImplementedException(); }
         }
+
+        public Point TranslatePointToScreen(Point p)
+        {
+            throw new NotImplementedException();
+        }
     }
 }

Perspex.Controls/Platform/IPopupImpl.cs

@@ -12,6 +12,8 @@ namespace Perspex.Platform
 
     public interface IPopupImpl : ITopLevelImpl
     {
+        void SetPosition(Point p);
+
         void Show();
 
         void Hide();

Perspex.Controls/Platform/ITopLevelImpl.cs

@@ -30,5 +30,7 @@ namespace Perspex.Platform
         void Invalidate(Rect rect);
 
         void SetOwner(TopLevel owner);
+
+        Point PointToScreen(Point point);
     }
 }

Perspex.Controls/Popup.cs

@@ -18,6 +18,9 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<bool> IsOpenProperty =
             PerspexProperty.Register<Popup, bool>("IsOpen");
 
+        public static readonly PerspexProperty<Control> PlacementTargetProperty =
+            PerspexProperty.Register<Popup, Control>("PlacementTarget");
+
         private PopupRoot root;
 
         private Window window;
@@ -54,6 +57,12 @@ namespace Perspex.Controls
             set { this.SetValue(IsOpenProperty, value); }
         }
 
+        public Control PlacementTarget
+        {
+            get { return this.GetValue(PlacementTargetProperty); }
+            set { this.SetValue(PlacementTargetProperty, value); }
+        }
+
         public void Open()
         {
             if (this.root == null)
@@ -62,6 +71,7 @@ namespace Perspex.Controls
                 this.root[~PopupRoot.ContentProperty] = this[~ChildProperty];
             }
 
+            this.root.SetPosition(this.GetPosition());
             this.root.Show();
         }
 
@@ -84,5 +94,17 @@ namespace Perspex.Controls
             base.OnDetachedFromVisualTree(oldRoot);
             this.window = null;
         }
+
+        private Point GetPosition()
+        {
+            if (this.PlacementTarget != null)
+            {
+                return this.PlacementTarget.PointToScreen(new Point(0, this.PlacementTarget.ActualSize.Height));
+            }
+            else
+            {
+                return new Point();
+            }
+        }
     }
 }

Perspex.Controls/PopupRoot.cs

@@ -27,6 +27,11 @@ namespace Perspex.Controls
             get { return (IPopupImpl)base.PlatformImpl; }
         }
 
+        public void SetPosition(Point p)
+        {
+            this.PlatformImpl.SetPosition(p);
+        }
+
         public void Hide()
         {
             this.PlatformImpl.Hide();

Perspex.Controls/TopLevel.cs

@@ -131,7 +131,12 @@ namespace Perspex.Controls
         {
             get { return this.renderManager; }
         }
-        
+
+        Point IRenderRoot.TranslatePointToScreen(Point p)
+        {
+            return this.PlatformImpl.PointToScreen(p);
+        }
+
         protected IDisposable BeginAutoSizing()
         {
             this.autoSizing = true;

Perspex.SceneGraph.UnitTests/TestRoot.cs

@@ -20,5 +20,10 @@ namespace Perspex.SceneGraph.UnitTests
         {
             get { throw new NotImplementedException(); }
         }
+
+        public Point TranslatePointToScreen(Point p)
+        {
+            throw new NotImplementedException();
+        }
     }
 }

Perspex.SceneGraph/Point.cs

@@ -77,11 +77,21 @@ namespace Perspex
             return new Point(a.x + b.x, a.y + b.y);
         }
 
+        public static Point operator +(Point a, Vector b)
+        {
+            return new Point(a.x + b.X, a.y + b.Y);
+        }
+
         public static Point operator -(Point a, Point b)
         {
             return new Point(a.x - b.x, a.y - b.y);
         }
 
+        public static Point operator -(Point a, Vector b)
+        {
+            return new Point(a.x - b.X, a.y - b.Y);
+        }
+
         public static Point operator *(Point point, Matrix matrix)
         {
             return new Point(

Perspex.SceneGraph/Rendering/IRenderRoot.cs

@@ -13,5 +13,7 @@ namespace Perspex.Rendering
         IRenderer Renderer { get; }
 
         IRenderManager RenderManager { get; }
+
+        Point TranslatePointToScreen(Point p);
     }
 }

Perspex.SceneGraph/Visual.cs

@@ -14,6 +14,7 @@ namespace Perspex
     using Perspex.Animation;
     using Perspex.Collections;
     using Perspex.Media;
+    using Perspex.Platform;
     using Perspex.Rendering;
     using Perspex.VisualTree;
     using Splat;
@@ -118,10 +119,16 @@ namespace Perspex
             Contract.Requires<ArgumentNullException>(context != null);
         }
 
+        public Point PointToScreen(Point point)
+        {
+            var p = GetOffsetFromRoot(this);
+            return p.Item1.TranslatePointToScreen(point + p.Item2);
+        }
+
         public Matrix TransformToVisual(IVisual visual)
         {
-            var thisOffset = GetOffsetFromRoot(this);
-            var thatOffset = GetOffsetFromRoot(visual);
+            var thisOffset = GetOffsetFromRoot(this).Item2;
+            var thatOffset = GetOffsetFromRoot(visual).Item2;
             return Matrix.Translation(-thisOffset) * Matrix.Translation(thatOffset);
         }
 
@@ -198,7 +205,7 @@ namespace Perspex
             }
         }
 
-        private static Vector GetOffsetFromRoot(IVisual v)
+        private static Tuple<IRenderRoot, Vector> GetOffsetFromRoot(IVisual v)
         {
             var result = new Vector();
 
@@ -206,9 +213,14 @@ namespace Perspex
             {
                 result = new Vector(result.X + v.Bounds.X, result.Y + v.Bounds.Y);
                 v = v.VisualParent;
+
+                if (v == null)
+                {
+                    throw new InvalidOperationException("Control is not attached to visual tree.");
+                }
             }
 
-            return result;
+            return Tuple.Create((IRenderRoot)v, result);
         }
 
         private static void RenderTransformChanged(PerspexPropertyChangedEventArgs e)

Perspex.Themes.Default/DropDownStyle.cs

@@ -82,6 +82,7 @@ namespace Perspex.Themes.Default
                         new Popup
                         {
                             Child = new TextBlock { Text = "Hello World" },
+                            PlacementTarget = control,
                             [~Popup.IsOpenProperty] = control[~DropDown.IsDropDownOpenProperty],
                         }
                     },

Windows/Perspex.Win32/PopupImpl.cs

@@ -12,6 +12,18 @@ namespace Perspex.Win32
 
     public class PopupImpl : WindowImpl, IPopupImpl
     {
+        public void SetPosition(Point p)
+        {
+            UnmanagedMethods.SetWindowPos(
+                this.Handle.Handle, 
+                IntPtr.Zero, 
+                (int)p.X, 
+                (int)p.Y, 
+                0,
+                0,
+                UnmanagedMethods.SetWindowPosFlags.SWP_NOSIZE);
+        }
+
         protected override IntPtr CreateWindowOverride(ushort atom)
         {
             UnmanagedMethods.WindowStyles style =

Windows/Perspex.Win32/WindowImpl.cs

@@ -111,6 +111,13 @@ namespace Perspex.Win32
             UnmanagedMethods.InvalidateRect(this.hwnd, ref r, false);
         }
 
+        public Point PointToScreen(Point point)
+        {
+            var p = new UnmanagedMethods.POINT { X = (int)point.X, Y = (int)point.Y };
+            UnmanagedMethods.ClientToScreen(this.hwnd, ref p);
+            return new Point(p.X, p.Y);
+        }
+
         public void SetOwner(TopLevel owner)
         {
             this.owner = owner;