f64/d2/rect.go
func RectWH(x, y, w, h float64) Rectangle {
	return Rectangle{
		Min: Vec{x, y},
		Max: Vec{x + w, y + h},
	}
}
func RectWH(x, y, w, h float64) Rectangle {
	return Rectangle{
		Min: Vec{x, y},
		Max: Vec{x + w, y + h},
	}
}
// RectWH returns a rectangle whose origin is Vec{x,y}, w and h are its width
// and height.