Transparency effect does not work on Fedora GNOME

Describe the bug When the TransparencyLevelHint property of a window is set to e.g. AcrylicBlur and the window background is (partially-)transparent (Background="#C0000000" or Background="{x:Null}"), the transparency effect is not visible on Fedora with GNOME.

@Splitwirez Ran the very same binaries on his linux system and the transparency was visible there. So it has probably something to do with my distribution or GNOME.

Gitter.im chat history of us trying to track this down: 22. Januar 2021 22:21

To Reproduce Steps to reproduce the behavior:

1. Create a new application using the avalonia.app dotnet-new template
2. Edit MainWindow.axaml and add TransparencyLevelHint="AcrylicBlur" Background="#C0000000" to the window.
3. dotnet run
4. A black window is shown with no transparency.

I’m able to reproduce this on two different machines (one with NVIDIA graphics, one with Intel graphics) with X11 and Wayland.

Expected behavior

• A (partially) transparent window pops up as it does on other systems.
• In cases, where transparency is not supported, I would expect a noisy gray background, like it’s also visible in the Controls Gallery app.

Screenshots Test application:

Controls Gallery (no transparency too, but gray background):

Desktop:

• OS: Linux, Fedora 33, GNOME Desktop
• Desktop Environment: GNOME 3.38.2
• Version: 0.10.0 stable release

Minimal example project Here is the minimal project that I used to reproduce the issue as well as the binaries: https://drive.wichelmann.cloud/s/3JYtWjEbCzmbin3

[kekekeks]

So it’s only making the wrong decision for the fallback?

Yes, which is either a bug or API design issue. We probably need TransparencyFallbackMode property to control that behavior.

[kekekeks]

Mkay, reproduced with nvidia + bumblebee