migu/common/modules/scroll.js

import { settings } from '@/modules/settings.js'

export default function (t, { speed = 120, smooth = 10 } = {}) {
  if (!settings.value.smoothScroll) return
  let moving = false
  let pos = 0
  let scrollTop = 0
  let lastTime = null
  t.addEventListener('wheel', e => {
    e.preventDefault()
    // is trackpad
    const spd = (e.deltaY !== (e.deltaY | 0) || e.wheelDelta % 10 !== 0) ? speed / 10 : speed
    pos = Math.max(0, Math.min(pos - Math.max(-1, Math.min(1, e.deltaY * -1)) * spd, (t.scrollHeight - t.clientHeight) + (smooth * 2)))
    if (!moving) {
      lastTime = null
      update()
    }
  }, { capture: true, passive: false })

  function getDeltaTime () {
    const now = performance.now()
    if (!lastTime) {
      lastTime = now
      return 1
    }
    const deltaTime = now - lastTime
    lastTime = now
    return deltaTime / 14
  }

  t.addEventListener('scrolltop', () => {
    pos = 0
    t.scrollTop = scrollTop
    if (!moving) {
      lastTime = null
      update()
    }
  })

  t.addEventListener('pointerup', () => { pos = scrollTop = t.scrollTop })

  function update () {
    const delta = pos - scrollTop === smooth * 2 ? 0 : ((pos - scrollTop) / smooth) * getDeltaTime()
    scrollTop += delta

    t.scrollTo(0, scrollTop < 1.3 ? 0 : scrollTop)
    moving = Math.abs(delta) > 0.1 && !!requestAnimationFrame(update)
  }
}