Rename projects to better structure it. The aim is to try and keep it not dependant on the type of UI framework it uses thus allowing us to switch to another UI framework if we need later...

Hyperbar.Windows.Controls/DesktopFlyout/DesktopFlyout.cs

@@ -0,0 +1,56 @@
+using Microsoft.UI.Xaml;
+
+namespace Hyperbar.Windows.Controls;
+
+public class DesktopFlyout :
+    DependencyObject
+{
+    public static readonly DependencyProperty ContentProperty =
+        DependencyProperty.Register(nameof(Content),
+            typeof(object), typeof(DesktopFlyout),
+            new PropertyMetadata(null));
+
+    public static readonly DependencyProperty PlacementProperty =
+        DependencyProperty.Register(nameof(Placement),
+            typeof(DesktopFlyoutPlacement), typeof(DesktopFlyout),
+            new PropertyMetadata(DesktopFlyoutPlacement.Left, OnPlacementPropertyChanged));
+
+    private readonly DesktopFlyoutHost host;
+    private readonly DesktopFlyoutPresenter presenter;
+
+    public DesktopFlyout()
+    {
+        presenter = new DesktopFlyoutPresenter
+        {
+            Parent = this
+        };
+
+        host = new DesktopFlyoutHost(presenter);
+        host.Activate();
+    }
+
+    public object Content
+    {
+        get => GetValue(ContentProperty);
+        set => SetValue(ContentProperty, value);
+    }
+
+    public DesktopFlyoutPlacement Placement
+    {
+        get => (DesktopFlyoutPlacement)GetValue(PlacementProperty);
+        set => SetValue(PlacementProperty, value);
+    }
+
+    private static void OnPlacementPropertyChanged(DependencyObject dependencyObject,
+        DependencyPropertyChangedEventArgs args)
+    {
+        if (dependencyObject is DesktopFlyout sender)
+        {
+            sender.OnPlacementPropertyChanged();
+        }
+    }
+
+    private void OnPlacementPropertyChanged() => UpdatePlacement();
+
+    private void UpdatePlacement() => host.UpdatePlacement(Placement);
+}