GetAlphaMask() visual empty for Path

[abrown313]

Describe the bug

When calling Shape.GetAlphaMask on a Microsoft.UI.Xaml.Shapes.Path, no visual is returned.

Steps to reproduce the bug

XAML

<Canvas>
    <Rectangle x:Name="ShadowHost" Height="400" Width="400" Canvas.Left="0" Canvas.Top="0"/>
    <TextBlock x:Name="MyText" Foreground="Black" Canvas.Left="0" Canvas.Top="0">Testing</TextBlock>
    <Rectangle x:Name="MyRectangle" Fill="Black" Canvas.Left="0" Canvas.Top="0" Height="100" Width="200"/>
    <Path x:Name="MyOtherPath" Fill="Black" Canvas.Left="0" Canvas.Top="0">
        <Path.Data>
            <GeometryGroup>
                <RectangleGeometry Rect="0,0,200,100"/>
            </GeometryGroup>
        </Path.Data>
    </Path>
</Canvas>

CPP

auto hostVisual = winrt::Microsoft::UI::Xaml::Hosting::ElementCompositionPreview::GetElementVisual(ShadowHost());
auto compositor = hostVisual.Compositor();

auto dropShadow = compositor.CreateDropShadow();
dropShadow.Color(winrt::Windows::UI::ColorHelper::FromArgb(255, 0, 0, 0));
dropShadow.BlurRadius(25);
dropShadow.Opacity(0.5);
auto pathMask = MyOtherPath().GetAlphaMask();
dropShadow.Mask(pathMask);

auto spriteVisual = compositor.CreateSpriteVisual();
spriteVisual.Size({ 400,400 });
spriteVisual.Shadow(dropShadow);

winrt::Microsoft::UI::Xaml::Hosting::ElementCompositionPreview::SetElementChildVisual(ShadowHost(), spriteVisual);

With auto pathMask = MyOtherPath().GetAlphaMask();, no shadow is created. I know the visual is empty because I also tried setting the GetAlphaMask output directly to the host visual which worked for the other shapes/text but not the Path.

Expected behavior

I'd expect the code above produce the same results as with the Rectangle shape directly. Then, I'd expect to also be able to generate masks/shadows for arbitrary geometry within the path (e.g. closed, filled path figures).

Screenshots

auto pathMask = MyRectangle().GetAlphaMask();

auto pathMask = MyText().GetAlphaMask();

NuGet package version

WinUI 3 - Windows App SDK 1.5.6: 1.5.240802000

Windows version

No response

Additional context

No response

[abrown313]

Resolved by giving the Path explicit width & height. Did this precisely in code behind using the Path data's Geometry.Bounds.