Fullscreen window width greater than screen width

Describe the bug When the application is in the fullscreen state the width is greater than my screen size. This may cause some elements to be not fully displayed.

To Reproduce Steps to reproduce the behavior:

• Create a new project from Avalonia MVVM template
• Add ExtendClientAreaToDecorationsHint="true" to MainWindow.axaml
• Change the alignment of the text to HorizontalAlignment="Left"
• Run the app and change the state to fullscreen

Expected behavior The message should be fully visible

Screenshots Screen from the debugger (My screen resolution is 1920x1080px):

Example of the bug:

Desktop (please complete the following information):

• OS: Windows 10
• Version 0.10.0

Additional context At first, I thought it is the bug in https://github.com/AvaloniaUI/XamlControlsGallery/issues/8 , but it is reproducible for all windows that use ExtendClientAreaToDecorationsHint="true".

[amwx]

This is a Win32 thing. To hide the system border when maximized, Windows enlarges the window ~8px on each side, but when the frame is extended, windows doesn’t turn this logic off automatically and requires special handling of WM_NCCALCSIZE to adjust the client rect which is now the whole window.

The simplest solution though is just to add 8px of padding to the window only when maximized:

<Style Selector="Window[WindowState=Maximized]">
        <Setter Property="Padding" Value="8" />
</Style>

[radoslawik]

It hasn’t been fixed yet, the issue can be reproduced in version 0.10.13