Added Window::HasSystemDecorations property

src/Android/Perspex.Android/Platform/SkiaPlatform/WindowImpl.cs

@@ -94,6 +94,9 @@ namespace Perspex.Android.Platform.SkiaPlatform
             this.Visibility = ViewStates.Invisible;
         }
 
+        public void SetSystemDecorations(bool enabled)
+        {
+        }
         public void Invalidate(Rect rect)
         {
             if (Holder?.Surface?.IsValid == true) base.Invalidate();

src/Gtk/Perspex.Gtk/WindowImpl.cs

@@ -170,6 +170,8 @@ namespace Perspex.Gtk
             return Disposable.Empty;
         }
 
+        public void SetSystemDecorations(bool enabled) => Decorated = enabled;
+
         void ITopLevelImpl.Activate()
         {
             Activate();

src/Perspex.Controls/Platform/IWindowImpl.cs

@@ -33,5 +33,10 @@ namespace Perspex.Platform
         /// Hides the window.
         /// </summary>
         void Hide();
+
+        /// <summary>
+        /// Enables of disables system window decorations (title bar, buttons, etc)
+        /// </summary>
+        void SetSystemDecorations(bool enabled);
     }
 }

src/Perspex.Controls/Platform/PlatformManager.cs

@@ -178,6 +178,7 @@ namespace Perspex.Controls.Platform
             public IDisposable ShowDialog() => _window.ShowDialog();
 
             public void Hide() => _popup.Hide();
+            public void SetSystemDecorations(bool enabled) => _window.SetSystemDecorations(enabled);
         }
 
         public static IWindowImpl CreateWindow()

src/Perspex.Controls/Window.cs

@@ -49,6 +49,12 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<SizeToContent> SizeToContentProperty =
             PerspexProperty.Register<Window, SizeToContent>(nameof(SizeToContent));
 
+        /// <summary>
+        /// Enables of disables system window decorations (title bar, buttons, etc)
+        /// </summary>
+        public static readonly PerspexProperty<bool> HasSystemDecorationsProperty =
+            PerspexProperty.Register<Window, bool>(nameof(HasSystemDecorations), true);
+
         /// <summary>
         /// Defines the <see cref="Title"/> property.
         /// </summary>
@@ -66,6 +72,8 @@ namespace Perspex.Controls
         {
             BackgroundProperty.OverrideDefaultValue(typeof(Window), Brushes.White);
             TitleProperty.Changed.AddClassHandler<Window>((s, e) => s.PlatformImpl.SetTitle((string)e.NewValue));
+            HasSystemDecorationsProperty.Changed.AddClassHandler<Window>(
+                (s, e) => s.PlatformImpl.SetSystemDecorations((bool) e.NewValue));
         }
 
         /// <summary>
@@ -114,6 +122,16 @@ namespace Perspex.Controls
             set { SetValue(TitleProperty, value); }
         }
 
+        /// <summary>
+        /// Enables of disables system window decorations (title bar, buttons, etc)
+        /// </summary>
+        /// 
+        public bool HasSystemDecorations
+        {
+            get { return GetValue(HasSystemDecorationsProperty); }
+            set { SetValue(HasSystemDecorationsProperty, value); }
+        }
+
         /// <inheritdoc/>
         Type IStyleable.StyleKey => typeof(Window);
 

src/Windows/Perspex.Win32/Interop/UnmanagedMethods.cs

@@ -571,6 +571,9 @@ namespace Perspex.Win32.Interop
         [DllImport("user32.dll", SetLastError = true)]
         public static extern uint GetWindowLong(IntPtr hWnd, int nIndex);
 
+        [DllImport("user32.dll", SetLastError = true)]
+        public static extern uint SetWindowLong(IntPtr hWnd, int nIndex, uint value);
+
         [DllImport("user32.dll")]
         public static extern bool GetWindowRect(IntPtr hwnd, out RECT lpRect);
 

src/Windows/Perspex.Win32/WindowImpl.cs

@@ -37,6 +37,8 @@ namespace Perspex.Win32
 
         private bool _isActive;
 
+        private bool _decorated = true;
+
         public WindowImpl()
         {
             CreateWindow();
@@ -145,6 +147,47 @@ namespace Perspex.Win32
             UnmanagedMethods.ShowWindow(_hwnd, UnmanagedMethods.ShowWindowCommand.Hide);
         }
 
+        public void SetSystemDecorations(bool value)
+        {
+            if (value == _decorated)
+                return;
+            var style = (UnmanagedMethods.WindowStyles) UnmanagedMethods.GetWindowLong(_hwnd, -16);
+            style |= UnmanagedMethods.WindowStyles.WS_OVERLAPPEDWINDOW;
+            if (!value)
+                style ^= UnmanagedMethods.WindowStyles.WS_OVERLAPPEDWINDOW;
+
+            UnmanagedMethods.RECT windowRect;
+
+            UnmanagedMethods.GetWindowRect(_hwnd, out windowRect);
+            Rect newRect;
+            var oldThickness = BorderThickness;
+
+            UnmanagedMethods.SetWindowLong(_hwnd, -16, (uint) style);
+            if (value)
+            {
+                var thickness = BorderThickness;
+                newRect = new Rect(
+                    windowRect.left - thickness.Left,
+                    windowRect.top - thickness.Top,
+                    (windowRect.right - windowRect.left) + (thickness.Left + thickness.Right),
+                    (windowRect.bottom - windowRect.top) + (thickness.Top + thickness.Bottom));
+            }
+            else
+                newRect = new Rect(
+                    windowRect.left + oldThickness.Left,
+                    windowRect.top + oldThickness.Top,
+                    (windowRect.right - windowRect.left) - (oldThickness.Left + oldThickness.Right),
+                    (windowRect.bottom - windowRect.top) - (oldThickness.Top + oldThickness.Bottom));
+            UnmanagedMethods.SetWindowPos(_hwnd, IntPtr.Zero, (int) newRect.X, (int) newRect.Y, (int) newRect.Width,
+                (int) newRect.Height,
+                UnmanagedMethods.SetWindowPosFlags.SWP_NOZORDER | UnmanagedMethods.SetWindowPosFlags.SWP_NOACTIVATE);
+
+
+            _decorated = value;
+
+
+        }
+
         public void Invalidate(Rect rect)
         {
             var r = new UnmanagedMethods.RECT

src/iOS/Perspex.iOS/PerspexView.cs

@@ -124,6 +124,11 @@ namespace Perspex.iOS
             //Not supported
         }
 
+        public void SetSystemDecorations(bool enabled)
+        {
+            //Not supported
+        }
+
         public override void TouchesEnded(NSSet touches, UIEvent evt)
         {
             var touch = touches.AnyObject as UITouch;