Get the Mica transparency level from WinUI 3

[onionware-github]

Hi, I want to add Mica to my FluentAvalonia app, but I dont get the right transparency for my page background to achieve the same colors that my WinUI 3 version of my app has:
I use the WindowsUIComposition and Background="Transparent" in my MainWindow.
Here are screenshots from the Avalonia version:

Here are screenshots of the WinUI 3 version of my app:

You can see that the WInUI version only uses a little amount of Mica transparency, but the Avalonia version has too much Mica.
The Avalonia version should have the same style as the WinUI 3 version, does anybody know the correct values, that I have to use as my page background to achieve the same look?

[amwx]

FWIW I've opened an issue upstream about this: AvaloniaUI/Avalonia#10719

The Mica brush isn't properly created upstream, it just pulls the blurred wallpaper from the WinUI compositor and returns. Unfortunately, this likely won't be fixed anytime soon given restrictions upstream until 11.0 is released. In the meantime you can try to do what I do in the sample app:

FluentAvalonia/samples/FluentAvaloniaSamples/Views/MainWindow.axaml.cs

Lines 143 to 168 in 8636ee6

	// The background colors for the Mica brush are still based around SolidBackgroundFillColorBase resource
	// BUT since we can't control the actual Mica brush color, we have to use the window background to create
	// the same effect. However, we can't use SolidBackgroundFillColorBase directly since its opaque, and if
	// we set the opacity the color become lighter than we want. So we take the normal color, darken it and
	// apply the opacity until we get the roughly the correct color
	// NOTE that the effect still doesn't look right, but it suffices. Ideally we need access to the Mica
	// CompositionBrush to properly change the color but I don't know if we can do that or not
	if (ActualThemeVariant == ThemeVariant.Dark)
	{
	var color = this.TryFindResource("SolidBackgroundFillColorBase",
	ThemeVariant.Dark, out var value) ? (Color2)(Color)value : new Color2(32, 32, 32);
	color = color.LightenPercent(-0.8f);
	Background = new ImmutableSolidColorBrush(color, 0.78);
	}
	else if (ActualThemeVariant == ThemeVariant.Light)
	{
	// Similar effect here
	var color = this.TryFindResource("SolidBackgroundFillColorBase",
	ThemeVariant.Light, out var value) ? (Color2)(Color)value : new Color2(243, 243, 243);
	color = color.LightenPercent(0.5f);
	Background = new ImmutableSolidColorBrush(color, 0.9);
	}

It doesn't look very good, but its something.