ICustomHitTest not working

[pr8x]

Describe the bug
It seems that implementing ICustomHitTest on Shape doesn't have any effect. It does work with the immediate renderer UseDeferredRendering=false) though.

To Reproduce

shape_custom_hittesting_bug.patch.txt

Expected behavior
I would expect the custom hit testing to work.

Desktop (please complete the following information):

• OS: Windows 10
• Version: master

[grokys]

Yeah, ICustomHitTest only works with the immediate renderer at the moment. I do notice that WPF seems to allow customizing hit testing by overriding HitTestCore - it might be that we need to implement this in Avalonia (which it would make sense to do with ICustomHitTest).

[grokys]

Actually, ignore the above comment. It was implemented for the deferred renderer too in this commit:

f0eafa7

However note the comment:

/// Note that this interface can only used to make a portion of a control non-hittable, it
/// cannot expand the hittable area of a control.

Might this be what you were seeing?

[mat1jaczyyy]

Centering the line in the window in this example breaks on immediate renderer, it incorrectly hit tests in the top left corner

[RomanSoloweow]

When using a non-fill Rectangle as an Adorner, the method

Avalonia/src/Avalonia.Controls/Primitives/AdornerLayer.cs

Line 144 in 7842883

public bool HitTest(Point point) => Children.HitTestCustom(point);

returns true on the entire area, not just on the borders

As a result, all events of the Adorned element are blocked.