useTransform2.ts

function useTransform2(
  mv1: MotionValue,
  mv2: MotionValue,
  transformer: (v1, v2) => any
) {
  const mv = useMotionValue(0)
  React.useEffect(() => {
    const unsub1 = mv1.onChange(v1 => mv.set(transformer(v1, mv2.get())))
    const unsub2 = mv2.onChange(v2 => mv.set(transformer(mv1.get(), v2)))
    return () => {
      unsub1()
      unsub2()
    }
  }, [mv1, mv2, transformer, mv])
  return mv
}