CSS 特效

<script setup="props" lang="ts">
import { useRafFn } from '@vueuse/core'
import type { Fn } from '@vueuse/core'

const r180 = Math.PI
const r90 = Math.PI / 2
const r15 = Math.PI / 12
const color = '#88888850'

const el = ref<HTMLCanvasElement | null>(null)

const { random } = Math

const f = {
  start: () => {},
}

const init = ref(5)
const len = ref(5)
const stopped = ref(false)

function initCanvas(canvas: HTMLCanvasElement, width = 400, height = 400, _dpi?: number) {
  const ctx = canvas.getContext('2d')!

  const dpr = window.devicePixelRatio || 1
  // @ts-expect-error vendor prefix
  const bsr = ctx.webkitBackingStorePixelRatio || ctx.mozBackingStorePixelRatio || ctx.msBackingStorePixelRatio || ctx.oBackingStorePixelRatio || ctx.backingStorePixelRatio || 1

  const dpi = _dpi || dpr / bsr

  canvas.style.width = `${width}px`
  canvas.style.height = `${height}px`
  canvas.width = dpi * width
  canvas.height = dpi * height
  ctx.scale(dpi, dpi)

  return { ctx, dpi }
}

function polar2cart(x = 0, y = 0, r = 0, theta = 0) {
  const dx = r * Math.cos(theta)
  const dy = r * Math.sin(theta)
  return [x + dx, y + dy]
}

onMounted(async () => {
  const canvas = el.value!
  const { ctx } = initCanvas(canvas)
  const { width, height } = canvas

  let steps: Fn[] = []
  let prevSteps: Fn[] = []

  let iterations = 0

  const step = (x: number, y: number, rad: number) => {
    const length = random() * len.value

    const [nx, ny] = polar2cart(x, y, length, rad)

    ctx.beginPath()
    ctx.moveTo(x, y)
    ctx.lineTo(nx, ny)
    ctx.stroke()

    const rad1 = rad + random() * r15
    const rad2 = rad - random() * r15

    if (nx < -100 || nx > 500 || ny < -100 || ny > 500)
      return

    if (iterations <= init.value || random() > 0.5)
      steps.push(() => step(nx, ny, rad1))
    if (iterations <= init.value || random() > 0.5)
      steps.push(() => step(nx, ny, rad2))
  }

  let controls: ReturnType<typeof useRafFn>

  const frame = () => {
    iterations += 1
    prevSteps = steps
    steps = []

    if (!prevSteps.length) {
      controls.pause()
      stopped.value = true
    }
    prevSteps.forEach(i => i())
  }

  controls = useRafFn(frame, { immediate: false })

  f.start = () => {
    controls.pause()
    iterations = 0
    ctx.clearRect(0, 0, width, height)
    ctx.lineWidth = 1
    ctx.strokeStyle = color
    prevSteps = []
    steps = random() < 0.5
      ? [
          () => step(0, random() * 400, 0),
          () => step(400, random() * 400, r180),
        ]
      : [
          () => step(random() * 400, 0, r90),
          () => step(random() * 400, 400, -r90),
        ]
    controls.resume()
    stopped.value = false
  }

  f.start()
})
</script>

<template>
  <div>
    <canvas ref="el" width="400" height="400" border />
    <div hover:color-gray-600 duration-200 cursor-pointer mt-2 inline-block @click="f.start">
      restart
    </div>
  </div>
</template>

<script setup>
const text
  = 'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.'
</script>

<template>
  <div class="rounded p-2.5 text-gray-500 dark:text-white dark:bg-black">
    <div class="relative mt-3">
      <div>
        {{ text }}
      </div>
      <div class="absolute inset-0">
        <span class="reveal">
          {{ text }}
        </span>
      </div>
    </div>
  </div>
</template>

<style scoped>
.reveal {
  color: transparent;
  background: linear-gradient(to right, transparent var(--p), #fff calc(var(--p) + 3em));
  animation: reveal 6s linear infinite forwards;
}
html.dark .reveal {
  background: linear-gradient(to right, transparent var(--p), #000 calc(var(--p) + 3em));
}

/* Houdini API */
@property --p {
  syntax: '<percentage>';
  initial-value: 0%;
  inherits: false;
}

@keyframes reveal {
  to {
    --p: 100%;
  }
}
</style>