Enable GraphicsCaptureItem creation from Microsoft.UI.WindowId/DisplayId

[Copilot]

Microsoft.UI.Win32Interop.GetWindowIdFromWindow(hwnd) returns Microsoft.UI.WindowId, but Windows.Graphics.Capture.GraphicsCaptureItem.TryCreateFromWindowId expects Windows.UI.WindowId. Despite identical memory layout, the namespace gap forces developers into unsafe manual reinterpret hacks.

Changes

New API: Microsoft.Windows.Graphics.Capture.GraphicsCaptureItem

Static runtimeclass with two factory methods that use IGraphicsCaptureItemInterop COM interface directly, bypassing the Windows.UI.WindowId requirement entirely:

// Before: painful namespace mismatch, no supported path
var msWindowId = Microsoft.UI.Win32Interop.GetWindowIdFromWindow(hwnd);
// ❌ GraphicsCaptureItem.TryCreateFromWindowId(msWindowId); // wrong type!

// After: first-class interop
using Microsoft.Windows.Graphics.Capture;
var msWindowId = Microsoft.UI.Win32Interop.GetWindowIdFromWindow(hwnd);
var item = GraphicsCaptureItem.TryCreateFromWindowId(msWindowId); // ✅

• TryCreateFromWindowId(Microsoft.UI.WindowId) — extracts HWND from WindowId.Value, calls IGraphicsCaptureItemInterop::CreateForWindow
• TryCreateFromDisplayId(Microsoft.UI.DisplayId) — calls IGraphicsCaptureItemInterop::CreateForMonitor; covers the display capture interop gap symmetrically
• Both follow TryCreate* convention: return null on invalid handle or non-capturable target; propagate unexpected COM activation failures as exceptions per WinRT boundary policy

New files

• dev/Interop/GraphicsCapture/Microsoft.Windows.Graphics.Capture.idl
• dev/Interop/GraphicsCapture/GraphicsCaptureItem.{h,cpp}
• dev/Interop/GraphicsCapture/GraphicsCapture.vcxitems
• dev/Projections/CS/Microsoft.Windows.Graphics.Capture.Projection/
• test/GraphicsCaptureTests/ — API tests for null-WindowId and null-DisplayId guard conditions

Modified files

• dev/WindowsAppRuntime_DLL/WindowsAppRuntime_DLL.vcxproj — import new vcxitems
• dev/WindowsAppRuntime_DLL/pch.h — add winrt/Windows.Graphics.Capture.h
• build/NuSpecs/WindowsAppSDK-Nuget-Native.WinRt.props — register Microsoft.Windows.Graphics.Capture.winmd
• WindowsAppRuntime.sln — wire up all new projects

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Original prompt

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This section details on the original issue you should resolve

<issue_title>Enable creating GraphicsCaptureItem from HWND by resolving the WindowId namespace mismatch</issue_title>
<issue_description>I am developing a C# application using Windows.Graphics.Capture.
I am facing a friction point when trying to use GraphicsCaptureItem.TryCreateFromWindowId(Windows.UI.WindowId windowId).
While Microsoft.UI.Win32Interop.GetWindowIdFromWindow(hwnd) exists to bridge the Win32 and WinUI worlds,
it returns a Microsoft.UI.WindowId struct. However, the Capture API expects a Windows.UI.WindowId struct.
Although these two structs share the same memory layout (a single ulong Value),
they reside in different namespaces and lack a built-in conversion or shared interface.
This forces developers to perform manual bitwise copying or "fake" casts,
which feels like an unsupported hack rather than a first-class developer experience.

To improve the interoperability between Win32 and Windows.Graphics.Capture,
I request one of the following:

1.Direct HWND Support:
Add GraphicsCaptureItem.TryCreateFromHwnd(IntPtr hwnd) to bypass the WindowId confusion entirely.

2.Official Conversion Utility:
Provide a standard method such as WindowId.FromHwnd(IntPtr hwnd) that returns the correct WindowId type for the target API,
or a bridge between Microsoft.UI.WindowId and Windows.UI.WindowId.

3.Documentation Clarity:
If WindowId.Value is guaranteed to be the same as an HWND handle,
please explicitly state this in the official documentation so developers can perform the cast safely.

The current lack of a clear, unified path for HWND-based capture is a significant hurdle for modernizing Windows apps.
I hope to see a more streamlined Interop experience in future updates.

Thank you for your consideration.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Enable creating GraphicsCaptureItem from HWND by resolving the WindowId namespace mismatch #6275

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