struct Rect: bool IsEmpty() const { return bottom <= top || right <= left; };

[geotyper]

In struct rRect:
Rect() :
left(0),
top(0),
right(0),
bottom(0) {}
top is top coordinate, so it need be bigger than bottom coordinate, only if we not in screen coordinates, where axis y is reversal to normal axis y.
All work, but need to swap in Rect init bottom and top coordinates.
Thanks for attention.

Post remark:
I found in closed issues your comment:
Well that depends on your graphics display. In Cartesian coordinates you're absolutely correct. But in many graphics display libraries, including those I've used in developing this library, they invert the Y axis so that values increasing from 0 as you move DOWN the Y axis. In other words, rather than the origin (0,0) being bottom left, the origin is top left.

But I think it need to add some words about that on your site in Coordinate Range.
Because it not often use reverse y in 2d engines and libs.
Or add some small functions or flags that invert y Axis, but also need to now screen size minimum by axis y.

[geotyper]

And one more comment:
For all other functions of lib it is critical to swap y axis or they symmetry in respect of axis y?

[AngusJohnson]

I'm not persuaded that this is an issue, nor do I understand you followup question.