Resizing window with full client rect Xaml Island draws window background first

[MarkIngramUK]

Describe the bug When resizing the main window, the result of WM_ERASEBKGND is drawn before the Xaml Island.

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Set the Xaml Island HWND size to be the full client rect of main window as a result of WM_SIZE (or WM_SIZING)
2. Resize the main window with the mouse
3. Example available at https://github.com/MarkIngramUK/XamlIslands

Expected behavior To not see the result of WM_ERASEBKGND (i.e. WndClassExW.hbrBackground) before the Xaml Island renders.

Screenshots The red is from wc.hbrBackground = CreateSolidBrush(RGB(255, 0, 0));, the blue is from the Xaml Island root content.

Version Info 1903

NuGet package version: N/A

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2019 Update (18362)	Yes
October 2018 Update (17763)	Yes
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)
Anniversary Update (14393)

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

Additional context You can largely hide the issue by specifying WS_EX_NOREDIRECTIONBITMAP on the main window, but it would be good if the Xaml Island rendered on resize, as it would make the resize seem smoother.

[marb2000]

This is a known limitation of XAML Islands v1 that should be addressed in WinUI 3 Islands.

[github-actions[bot]]

This issue is stale because it has been open 180 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[rpjohnst]

Not stale.