export function calcScrollRatio(
  scrollY: number,
  elementTop: number,
  elementHeight: number
): number {
  const h = elementHeight || 1;
  const raw = (scrollY - elementTop) / h;
  if (raw < 0) return 0;
  if (raw > 1) return 1;
  return raw;
}

export function scrollOffsetFromRatio(
  elementTop: number,
  elementHeight: number,
  ratio: number
): number {
  return elementTop + elementHeight * ratio;
}