Is there a way to prevent the background color resizing from being delayed when resizing the window?

[nathanAjacobs]

When I resize my window the background color is delayed to fill the whole window. Is there a way to fix this?

2022-06-01.18-17-48_Trim.mp4

[nathanAjacobs]

This actually seems to be a problem with WinUI 3 itself. Hoping a fix is released soon, this is a dealbreaker for me.

[jeromelaban]

In general, there's a delay when re-rendering the window content after a resize, and in general, this is handled by ensuring that the window background matches a color that won't be significantly different from the app's content.

Uno's targets also have the similar behavior, because the rendering is performed on a thread different from the windowing system's one. You'll see similar behavior on mobiles, particularly when changing screen orientations.

Also, if you're running the Skia+WPF head, the rendering is still done using software rendering, which makes it a bit slower than it could be. You can try with Skia+GTK using Uno 4.3.8, which uses OpenGL acceleration.

[nathanAjacobs]

Is it possible to change the Window background itself as you described? As far as I can tell, WinUI 3 XAML doesn't have a Background property on the Window class.

I also tried Skia+GTK, but the problem was still there.

[jeromelaban]

It's a question to ask on the WinUI repository.

For Skia+GTK, it's a similar problem to WinUI, though the API is likely to be different and we do not have one yet (Let's track it here #8961). For Skia+WPF, you can change the XAML in the WPF host to another color.

[nathanAjacobs]

@jeromelaban Maybe I'm misunderstanding, but setting the Window or ContentControl's background via XAML in WPF host has no effect. The only thing that has an effect is setting the background color in code behind like so:

public MainWindow()
{
    InitializeComponent();

    root.Content = new global::Uno.UI.Skia.Platform.WpfHost(Dispatcher, () => new TestUnoApp.App());
    var contentControl = root.Content as Uno.UI.Skia.Platform.WpfHost;
    contentControl.Background = new SolidColorBrush(new Color { R = 0, G = 0, B = 0, A = 128 });
}

But even that behaves weird because it actually draws on top of the regular shared apps content. For example the shared apps main Page has it's background set to orange but as you can see it draws on top, if I change the alpha value to 255 it completely blocks the shared app and just draws black.

2022-06-03.12-01-08_Trim.mp4

[nathanAjacobs]

I tried changing the canvas (first element in the uno tree) background color last night as well. Unfortunately, it just completely renders over the content from the shared app. So If I set the canvas background color to black, I just have a completely black window.

[jeromelaban]

Would you be able to post a small repro app which shows the issues your getting in the video?

[nathanAjacobs]

Yes, I can do this later tonight when I get home from work. I will update you later when it is up.

[nathanAjacobs]

Here is the demo WPF project which demonstrates this issue:

https://github.com/nathanAjacobs/UnoAppBackgroundBugWPF

In the MainWindow.xaml.cs file of the WPF host project, there are several commented out lines which sets various Background colors on the corresponding elements. If you uncomment the lines, you should see the behavior of it rendering the background over the shared app's content.

[jeromelaban]

Thanks for the repro. For Skia Gtk/WPF, this PR should help: #9039.