In WinUI 3, is it possible to create a transparent Xaml Island overlay on top of parent hwnd?

I have created a Xaml Island in a C++ Desktop Application:

    xaml_app_host_ = winrt::Microsoft::UI::Xaml::Application{};
    desktop_window_xaml_source_ = winrt::Microsoft::UI::Xaml::Hosting::DesktopWindowXamlSource{};
    desktop_window_xaml_source_.as<IDesktopWindowXamlSourceNative>()->AttachToWindow(window_);

I see the window created and the child corewindow and bridge window children under my main window:

Controls render fine, but the entire window turns black, covering contents rendered to the parent window. I would like the controls in the xaml island to show up overlaid on the contents rendered to the parent window (which is rendering at low latency and controlling the message pump).

This behavior happens even without any controls set to the content.

I have tried futzing with setting ws_ex_layered, and a COLORKEY:

        auto content_bridge = FindWindowEx(window_, NULL, L"Microsoft.UI.Input.DesktopWindowLiftedContentBridge", NULL);
        ::SetWindowLong(content_bridge, GWL_EXSTYLE, GetWindowLong(content_bridge, GWL_EXSTYLE) | WS_EX_LAYERED | WS_EX_TRANSPARENT);
        ::SetLayeredWindowAttributes(content_bridge, RGB(0,0,0), 0, LWA_COLORKEY);

Is this possible? If not, are there any work arounds?

[smk2007]

Hi is there any update on adding transparency to WinUI 3?

[annmanvel]

Hi,

I am new to UWP and WinUI 3.

I am currently working to make Transparent overlay and click through. Is it possible to achieve these functionalities using UWP(C#) or WinUI 3 in UWP (C#); without using win32 api dlls?

I have achieved transparency and click through with win32 api’s. But I need to know the possibilities other than win32 api’s .