// How the wheel moves a view that zooms: a pinch moves a few pixels at a time,
// a mouse wheel's notch a hundred or so (or a few lines), so a notch is one
// fixed step rather than a jump.

const NOTCH = 1.1;

/** A wheel delta in pixels, a line counting as 40. */
export function pixels(event: WheelEvent, delta: number): number {
  return event.deltaMode === WheelEvent.DOM_DELTA_PIXEL ? delta : delta * 40;
}

/** What a wheel event multiplies the zoom by. */
export function zoomFactor(event: WheelEvent): number {
  const moved = pixels(event, event.deltaY);
  return Math.abs(moved) >= 50 ? NOTCH ** -Math.sign(moved) : Math.exp(-moved * 0.01);
}