f32/d3/rect.go
func RectFromSphere(c Vec3, r float32) Rectangle {
	return RectWHD(c[0]-r, c[1]-r, c[2]-r, 2*r, 2*r, 2*r)
}
func RectFromSphere(c Vec3, r float32) Rectangle {
	return RectWHD(c[0]-r, c[1]-r, c[2]-r, 2*r, 2*r, 2*r)
}
// RectFromSphere returns the minimum rectangle that contains the circle of
// center c and radius r.