In WindowBase.PositionChanged event handler Point value is wrong

[sinatrocious]

Describe the bug

The value of PixelPointEvenArgs.Point inside event handler is wrong.

To Reproduce

Steps to reproduce the behavior:

1. Create new Avalonia C# project.
2. In MainWindow.axaml.cs add line in constructor to output argument value and actual value:

    public MainWindow()
    {
        InitializeComponent();
        PositionChanged += (s, e) => Debug.WriteLine($"Position={e.Point}, actual={Position}");
        //Position = new(666, 666); // optional
    }

3. Run and observe debugger "Output" window.
4. My outputs are

Position=190, 213, actual=188, 182
or
Position=668, 697, actual=666, 666

Expected behavior

I expect e.Point value to be equal to actual window Position.

Environment

• OS: Windows 11
• Avalonia-Version: 11.0.9

Additional context

I tried to use PositionChanged event to store position of window in normal state, see #14517 ,but unfortunately discovered a new frustrating bug in Avalonia.

[TomEdwardsEnscape]

Looks like Position is considered the position of the client area in some places, and the position of the window frame in others.

[TomEdwardsEnscape]

Maximising the window reveals that e.Point is the location of the client area, but Position is the location of the whole window including its frame.

Position=0, 23, actual=-1, -8

The raw value that comes from GetWindowRect is -8, -8. An attempt is being made to counteract the window's drop shadow, but it doesn't seem to be working very well.

What should the Position property really represent? The client area? The window frame? (I think we can discard the option of the window frame including drop shadow.)

[maxkatz6]

cc @emmauss