f64/d2/rect.go
func RectFromCircle(c Vec, r float64) Rectangle {
	return RectWH(c.X-r, c.Y-r, 2*r, 2*r)
}
func RectFromCircle(c Vec, r float64) Rectangle {
	return RectWH(c.X-r, c.Y-r, 2*r, 2*r)
}
// RectFromCircle returns the minimum rectangle that contains the circle of
// center c and radius r