Edge case in Rect.Intersect

[grokys]

Describe the bug

Calling Rect.Intersect with a rect that has a width or height (but not both) of 0 erroneously results in an empty rect.

To Reproduce

[Fact]
public void Intersect_Should_Handle_Height_0()
{
    var r1 = new Rect(0, 0, 100, 0);
    var r2 = new Rect(0, 0, 50, 0);
    var result = r1.Intersect(r2);

    Assert.Equal(new Rect(0, 0, 50, 0), result);
}

[Fact]
public void Intersect_Should_Handle_Width_0()
{
    var r1 = new Rect(0, 0, 0, 100);
    var r2 = new Rect(0, 0, 0, 50);
    var result = r1.Intersect(r2);

    Assert.Equal(new Rect(0, 0, 0, 50), result);
}

Both fail because Intersect returns an empty rect.

Expected behavior

Should return a Rect with the intersection of the 0 width/height rect. Tested with WPF and this works correctly.

Avalonia version

all

OS

No response

Additional context

The code for Rect.Intersect was taken from SharpDX which also has this bug:

https://github.com/sharpdx/SharpDX/blob/master/Source/SharpDX.Mathematics/RectangleF.cs#L364-L378

Looks like the condition should use >= instead of >

[kekekeks]

Note that unlike Avalonia WPF treats zero-sized rects as non-empty. We should probably be doing the same.

I've been slowly replacing Rect with Rect? in relevant places of the rendering code to express Rect.Empty semantics from WPF.