Unable to cast Compositor to ICompositorInterop

Describe the bug In our WinUI for UWP app, we are trying to create an ICompositionGraphicsDevice2 instance as documented here. For this, we try to cast the Window.Current.Compositor instance to the ICompositorInterop interface:

var compositorPtr = Marshal.GetIUnknownForObject(Window.Current.Compositor);            
var guid = typeof(ICompositorInterop).GUID;
var hresult = Marshal.QueryInterface(compositorPtr, ref guid, out var pCompositorInterop);
var compositorInterop = (ICompositorInterop)Marshal.GetObjectForIUnknown(pCompositorInterop);

However, the QueryInterface returns the E_NOINTERFACE hresult.

I’ve listed available IIDs for the compositor object using the IInspectable API and have not found the ICompositorInterop iid (25297D5C-3AD4-4C9C-B5CF-E36A38512330)

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Download and run the sample from the Additional Context section
2. Click on the “Click Me” button
3. The exception will be thrown.

Expected behavior The ICompositorInterop should be available

Screenshots

Version Info

NuGet package version:

[Microsoft.WinUI 3.0.0-preview3.201113.0] [Microsoft.NETCore.UniversalWindowsPlatform 6.2.10]

Windows app type:

UWP	Win32
Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2020 Update (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

App6.zip

[alexserov]

@Scottj1s I tried your solution - it works like a charm, thanks!

Your link to the header file helped me a lot.

[Scottj1s]

@alexserov - my apologies, I missed that this was UWP.

It looks like you need to QI for the lifted compositor interop interface (in Microsoft.UI.Composition.Interop, rather than Windows.UI.Composition.Interop), which requires a GUID change. Also, the interop interface should be IUnknown, rather than IInspectable:

    [ComImport, Guid("FAB19398-6D19-4D8A-B752-8F096C396069"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]

For additional interop interfaces, see the nuget header: <nuget packages>\microsoft.winui\3.0.0-preview3.201113.0\include\Microsoft.UI.Composition.Interop.h