pub fn union_pt(&self, pt: Point) -> Rect {
        Rect::new(
            self.x0.min(pt.x),
            self.y0.min(pt.y),
            self.x1.max(pt.x),
            self.y1.max(pt.y),
        )
    }
Compute the union with one point.

This method includes the perimeter of zero-area rectangles.
Thus, a succession of `union_pt` operations on a series of
points yields their enclosing rectangle.

Results are valid only if width and height are non-negative.
common/src/geometry.rs