Add managed CaptionButtonsControl.

src/Avalonia.Controls/Chrome/CaptionButtons.cs

@@ -0,0 +1,89 @@
+using System;
+using System.Collections.Generic;
+using System.Reactive.Disposables;
+using System.Text;
+using Avalonia.Controls.Primitives;
+using Avalonia.VisualTree;
+
+namespace Avalonia.Controls.Chrome
+{
+    public class CaptionButtons : TemplatedControl
+    {
+        private CompositeDisposable _disposables;
+        private Window _hostWindow;
+
+        public CaptionButtons(Window hostWindow)
+        {
+            _hostWindow = hostWindow;
+        }
+
+        public void Attach()
+        {
+            if (_disposables == null)
+            {
+                var layer = ChromeOverlayLayer.GetOverlayLayer(_hostWindow);
+
+                layer.Children.Add(this);
+
+                _disposables = new CompositeDisposable
+                {
+                    _hostWindow.GetObservable(Window.WindowDecorationMarginsProperty)
+                    .Subscribe(x =>
+                    {
+                        Height = x.Top;
+                    }),
+
+
+                    _hostWindow.GetObservable(Window.ExtendClientAreaTitleBarHeightHintProperty)
+                    .Subscribe(x => InvalidateSize()),
+
+                    _hostWindow.GetObservable(Window.OffScreenMarginProperty)
+                    .Subscribe(x => InvalidateSize()),
+
+                    _hostWindow.GetObservable(Window.WindowStateProperty)
+                    .Subscribe(x =>
+                    {
+                        PseudoClasses.Set(":minimized", x == WindowState.Minimized);
+                        PseudoClasses.Set(":normal", x == WindowState.Normal);
+                        PseudoClasses.Set(":maximized", x == WindowState.Maximized);
+                        PseudoClasses.Set(":fullscreen", x == WindowState.FullScreen);
+                    })
+                };
+            }
+        }
+
+        void InvalidateSize ()
+        {
+            Margin = new Thickness(1, _hostWindow.OffScreenMargin.Top, 1, 1);
+            Height = _hostWindow.WindowDecorationMargins.Top - _hostWindow.OffScreenMargin.Top;
+        }
+
+        public void Detach()
+        {
+            if (_disposables != null)
+            {
+                var layer = ChromeOverlayLayer.GetOverlayLayer(_hostWindow);
+
+                layer.Children.Remove(this);
+
+                _disposables.Dispose();
+                _disposables = null;
+            }
+        }
+
+        protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+        {
+            base.OnApplyTemplate(e);
+
+            var closeButton = e.NameScope.Find<Panel>("PART_CloseButton");
+            var restoreButton = e.NameScope.Find<Panel>("PART_RestoreButton");
+            var minimiseButton = e.NameScope.Find<Panel>("PART_MinimiseButton");
+            var fullScreenButton = e.NameScope.Find<Panel>("PART_FullScreenButton");
+
+            closeButton.PointerPressed += (sender, e) => _hostWindow.Close();
+            restoreButton.PointerPressed += (sender, e) => _hostWindow.WindowState = _hostWindow.WindowState == WindowState.Maximized ? WindowState.Normal : WindowState.Maximized;
+            minimiseButton.PointerPressed += (sender, e) => _hostWindow.WindowState = WindowState.Minimized;
+            fullScreenButton.PointerPressed += (sender, e) => _hostWindow.WindowState = _hostWindow.WindowState == WindowState.FullScreen ? WindowState.Normal : WindowState.FullScreen;
+        }
+    }
+}

src/Avalonia.Controls/Primitives/ChromeOverlayLayer.cs

@@ -0,0 +1,37 @@
+using System.Linq;
+using Avalonia.Rendering;
+using Avalonia.VisualTree;
+
+namespace Avalonia.Controls.Primitives
+{
+    public class ChromeOverlayLayer : Canvas, ICustomSimpleHitTest
+    {
+        public Size AvailableSize { get; private set; }
+
+        public static ChromeOverlayLayer GetOverlayLayer(IVisual visual)
+        {
+            foreach (var v in visual.GetVisualAncestors())
+                if (v is VisualLayerManager vlm)
+                    if (vlm.OverlayLayer != null)
+                        return vlm.ChromeOverlayLayer;
+
+            if (visual is TopLevel tl)
+            {
+                var layers = tl.GetVisualDescendants().OfType<VisualLayerManager>().FirstOrDefault();
+                return layers?.ChromeOverlayLayer;
+            }
+
+            return null;
+        }
+
+        public bool HitTest(Point point) => Children.HitTestCustom(point);
+
+        protected override Size ArrangeOverride(Size finalSize)
+        {
+            // We are saving it here since child controls might need to know the entire size of the overlay
+            // and Bounds won't be updated in time
+            AvailableSize = finalSize;
+            return base.ArrangeOverride(finalSize);
+        }
+    }
+}

src/Avalonia.Controls/Primitives/VisualLayerManager.cs

@@ -6,7 +6,9 @@ namespace Avalonia.Controls.Primitives
     public class VisualLayerManager : Decorator
     {
         private const int AdornerZIndex = int.MaxValue - 100;
-        private const int OverlayZIndex = int.MaxValue - 99;
+        private const int ChromeZIndex = int.MaxValue - 99;
+        private const int OverlayZIndex = int.MaxValue - 98;
+
         private ILogicalRoot _logicalRoot;
         private readonly List<Control> _layers = new List<Control>();
         
@@ -24,6 +26,17 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
+        public ChromeOverlayLayer ChromeOverlayLayer
+        {
+            get
+            {
+                var rv = FindLayer<ChromeOverlayLayer>();
+                if (rv == null)
+                    AddLayer(rv = new ChromeOverlayLayer(), ChromeZIndex);
+                return rv;
+            }
+        }
+
         public OverlayLayer OverlayLayer
         {
             get

src/Avalonia.Controls/Properties/AssemblyInfo.cs

@@ -13,3 +13,4 @@ using Avalonia.Metadata;
 [assembly: XmlnsDefinition("https://github.com/avaloniaui", "Avalonia.Controls.Shapes")]
 [assembly: XmlnsDefinition("https://github.com/avaloniaui", "Avalonia.Controls.Templates")]
 [assembly: XmlnsDefinition("https://github.com/avaloniaui", "Avalonia.Controls.Notifications")]
+[assembly: XmlnsDefinition("https://github.com/avaloniaui", "Avalonia.Controls.Chrome")]

src/Avalonia.Themes.Default/CaptionButtons.xaml

@@ -0,0 +1,70 @@
+<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <Style Selector="CaptionButtons">
+    <Setter Property="Foreground" Value="{DynamicResource ThemeForegroundBrush}"/>
+    <Setter Property="Canvas.Right" Value="0" />
+    <Setter Property="MaxHeight" Value="30" />
+    <Setter Property="Template">
+      <ControlTemplate>
+        <StackPanel Spacing="2" Margin="0 0 7 0" Background="#7F00FF00" VerticalAlignment="Stretch" TextBlock.FontSize="10" Orientation="Horizontal">
+          <StackPanel.Styles>
+            <Style Selector="Panel">
+              <Setter Property="Width" Value="45" />
+              <Setter Property="Background" Value="Transparent" />
+            </Style>
+            <Style Selector="Path">
+              <Setter Property="Fill" Value="White" />
+            </Style>
+            <Style Selector="Panel:pointerover">
+              <Setter Property="Background" Value="#1FFFFFFF" />
+            </Style>
+            <Style Selector="Panel#PART_CloseButton:pointerover">
+              <Setter Property="Background" Value="#AFFF0000" />
+            </Style>
+            <Style Selector="Viewbox">
+              <Setter Property="Width" Value="11" />
+              <Setter Property="Margin" Value="2" />
+            </Style>
+          </StackPanel.Styles>
+          <Panel x:Name="PART_FullScreenButton">
+            <Viewbox>
+              <Path Stretch="UniformToFill" />
+            </Viewbox>
+          </Panel>
+
+          <Panel x:Name="PART_MinimiseButton">
+            <Viewbox>
+              <Path Stretch="UniformToFill" Data="M2048 1229v-205h-2048v205h2048z" />
+            </Viewbox>
+          </Panel>
+
+          <Panel x:Name="PART_RestoreButton">
+            <Viewbox>
+              <Viewbox.RenderTransform>
+                <RotateTransform Angle="-90" />
+              </Viewbox.RenderTransform>
+              <Path Stretch="UniformToFill"/>              
+            </Viewbox>
+          </Panel>
+
+          <Panel x:Name="PART_CloseButton">
+            <Viewbox>
+              <Path Stretch="UniformToFill" Data="M1169 1024l879 -879l-145 -145l-879 879l-879 -879l-145 145l879 879l-879 879l145 145l879 -879l879 879l145 -145z" />
+            </Viewbox>
+          </Panel>
+        </StackPanel>
+      </ControlTemplate>
+    </Setter>
+  </Style>
+  <Style Selector="CaptionButtons Panel#PART_RestoreButton Path">
+    <Setter Property="Data" Value="M2048 2048v-2048h-2048v2048h2048zM1843 1843h-1638v-1638h1638v1638z" />
+  </Style>
+  <Style Selector="CaptionButtons:maximized Panel#PART_RestoreButton Path">
+    <Setter Property="Data" Value="M2048 410h-410v-410h-1638v1638h410v410h1638v-1638zM1434 1434h-1229v-1229h1229v1229zM1843 1843h-1229v-205h1024v-1024h205v1229z" />
+  </Style>
+  <Style Selector="CaptionButtons Panel#PART_FullScreenButton Path">
+    <Setter Property="Data" Value="M2048 2048v-819h-205v469l-1493 -1493h469v-205h-819v819h205v-469l1493 1493h-469v205h819z" />
+  </Style>
+  <Style Selector="CaptionButtons:fullscreen Panel#PART_FullScreenButton Path">
+    <Setter Property="Data" Value="M205 1024h819v-819h-205v469l-674 -674l-145 145l674 674h-469v205zM1374 1229h469v-205h-819v819h205v-469l674 674l145 -145z" />
+  </Style>
+</Styles>

src/Avalonia.Themes.Default/DefaultTheme.xaml

@@ -9,6 +9,7 @@
   <StyleInclude Source="resm:Avalonia.Themes.Default.Button.xaml?assembly=Avalonia.Themes.Default"/>
   <StyleInclude Source="resm:Avalonia.Themes.Default.Carousel.xaml?assembly=Avalonia.Themes.Default"/>
   <StyleInclude Source="resm:Avalonia.Themes.Default.CheckBox.xaml?assembly=Avalonia.Themes.Default"/>
+  <StyleInclude Source="resm:Avalonia.Themes.Default.CaptionButtons.xaml?assembly=Avalonia.Themes.Default"/>
   <StyleInclude Source="resm:Avalonia.Themes.Default.ComboBox.xaml?assembly=Avalonia.Themes.Default"/>
   <StyleInclude Source="resm:Avalonia.Themes.Default.ComboBoxItem.xaml?assembly=Avalonia.Themes.Default"/>
   <StyleInclude Source="resm:Avalonia.Themes.Default.ContentControl.xaml?assembly=Avalonia.Themes.Default"/>