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27 Highlighter sweep

Motion · Type in motion
Highlighter sweep

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motion-highlighter-sweep-everything.md

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Prompt

1.2 KB 
Highlighter sweep — Highlighter sweep

Wrap the words to emphasise in <mark>, and when a word enters the viewport draw a highlighter line across it from left to right over 0.7 s.
Build the line as a linear-gradient background: the accent colour mixed at 32% with transparent, covering only the lower 62% of the word. Animate background-size alone, from 0% 100% to 100% 100%, with background-repeat: no-repeat and background-position: 0 0.
Start when 60% of the word is visible above a line 20% up from the bottom of the viewport, and when one sentence holds several words, delay each by 160 ms after the one before.
Give phrases that wrap box-decoration-break: clone so every line draws its own stroke from its left edge, and leave the text colour and weight untouched.
Implement with a CSS transition and IntersectionObserver only, no libraries.

Do not drop:
- Once drawn, the line stays even when the reader scrolls back
- Wrapped phrases use box-decoration-break: clone so the line is never cut mid-phrase
- Keep the line faint and behind the text, and leave the text colour as it is
- With reduced motion, show every line already drawn

A working example (one self-contained HTML file): https://design-vault.pages.dev/designs/motion-highlighter-sweep/demo.html

Files

demo.html

8.9 KB

/designs/motion-highlighter-sweep/demo.html — One self-contained HTML file. CSS and plain JavaScript only; it fetches nothing.

Show contents 
<!doctype html>
<html lang="ja">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>27 マーカー線 — Highlighter sweep</title>
<style>
/* dv-motion-base:start */
:root {
  --ground: #FFFFFF;
  --surface: #F3F5F8;
  --ink: #14181F;
  --muted: #5A6472;
  --accent: #1F5FA8;
  --rule: #D8DDE4;
  --accent-soft: color-mix(in srgb, var(--accent) 12%, var(--ground));
  --accent-mid: color-mix(in srgb, var(--accent) 45%, var(--ground));
  --shade: color-mix(in srgb, var(--ink) 14%, transparent);

  --font: "Zen Kaku Gothic New", "Hiragino Sans", "Noto Sans JP", "Yu Gothic", system-ui, sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;

  --t-label: 13px;
  --t-body: 16px;
  --t-lead: 20px;
  --t-h2: 32px;
  --t-h1: clamp(40px, 7vw, 72px);

  --s1: 4px;
  --s2: 8px;
  --s3: 16px;
  --s4: 24px;
  --s5: 40px;
  --s6: 64px;
  --s7: 104px;

  --radius: 12px;
  --ease: cubic-bezier(.2, .7, .2, 1);
  --dur: .7s;
  --measure: 1080px;
}
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--ground);
  color: var(--ink);
  font-family: var(--font);
  font-size: var(--t-body);
  line-height: 1.7;
  font-feature-settings: "palt";
  overflow-x: hidden;
}
h1, h2, h3, p, ul, ol, figure { margin: 0; padding: 0; }
ul, ol { list-style: none; }
.dv-wrap { width: min(100% - 2 * var(--s4), var(--measure)); margin-inline: auto; }
.dv-label {
  min-height: 72vh;
  display: grid;
  align-content: center;
  gap: var(--s3);
  padding-block: var(--s6);
  border-bottom: 1px solid var(--rule);
}
.dv-num { font-family: var(--mono); font-size: var(--t-lead); font-weight: 700; color: var(--accent); letter-spacing: .04em; }
.dv-name { font-size: var(--t-h1); font-weight: 700; line-height: 1.15; letter-spacing: .01em; }
.dv-ai { font-family: var(--mono); font-size: var(--t-lead); color: var(--muted); }
.dv-desc { font-size: var(--t-lead); color: var(--ink); }
.dv-hint { font-size: var(--t-label); color: var(--muted); letter-spacing: .12em; margin-top: var(--s4); }
.dv-stage { padding-block: var(--s7); }
.dv-h2 { font-size: var(--t-h2); font-weight: 700; line-height: 1.3; }
.dv-lead { font-size: var(--t-lead); color: var(--muted); }
.dv-eyebrow { font-family: var(--mono); font-size: var(--t-label); color: var(--accent); letter-spacing: .12em; text-transform: uppercase; }
.dv-card { background: var(--surface); border: 1px solid var(--rule); border-radius: var(--radius); padding: var(--s4); }
.dv-ph {
  border-radius: var(--radius);
  background: linear-gradient(135deg, var(--accent-soft), var(--accent-mid) 60%, var(--accent));
  aspect-ratio: 16 / 9;
}
.dv-ph--alt { background: linear-gradient(200deg, var(--surface), var(--accent-soft) 55%, var(--accent-mid)); }
.dv-ph--ink { background: linear-gradient(160deg, var(--ink), color-mix(in srgb, var(--ink) 55%, var(--accent))); }
.dv-end {
  min-height: 60vh;
  display: grid;
  place-items: center;
  border-top: 1px solid var(--rule);
  color: var(--muted);
  font-family: var(--mono);
  font-size: var(--t-label);
  letter-spacing: .12em;
}
/* dv-motion-base:end */

/* ---- この演出だけの CSS。色は var(--…) か color-mix() のみ ---- */
.hl-stack { display: grid; gap: var(--s7); }
.hl-block { display: grid; gap: var(--s3); align-content: center; min-height: 56vh; }
.hl-text { font-size: clamp(22px, 3.4vw, 40px); font-weight: 700; line-height: 1.9; }
/* 線は語の下 62% にだけ引く。折り返した行のそれぞれが自分の線を持つよう clone にする */
.hl {
  padding-inline: .12em;
  color: inherit;
  background-color: transparent;
  background-image: linear-gradient(to top, color-mix(in srgb, var(--accent) 32%, transparent) 62%, transparent 62%);
  background-repeat: no-repeat;
  background-position: 0 0;
  background-size: 100% 100%;
  -webkit-box-decoration-break: clone;
  box-decoration-break: clone;
  transition: background-size var(--dur) var(--ease) calc(var(--i, 0) * 160ms);
}
.js .hl { background-size: 0% 100%; }
.js .hl.is-in { background-size: 100% 100%; }

@media (prefers-reduced-motion: reduce) {
  .js .hl { background-size: 100% 100%; transition: none; }
}
</style>
</head>
<body data-motion-number="27">
<header class="dv-label">
  <div class="dv-wrap">
    <p class="dv-num">27</p>
    <h1 class="dv-name">マーカー線</h1>
    <p class="dv-ai">Highlighter sweep</p>
    <p class="dv-desc">文中の語にマーカーが引かれる</p>
    <p class="dv-hint">SCROLL ↓</p>
  </div>
</header>

<main class="dv-stage">
  <div class="dv-wrap hl-stack">
    <section class="hl-block">
      <p class="dv-eyebrow">Section 1</p>
      <p class="hl-text">ここには説明の文章が入ります。読んでほしい<mark class="hl">大事な語</mark>に、画面へ入った順でマーカーが引かれます。</p>
    </section>
    <section class="hl-block">
      <p class="dv-eyebrow">Section 2</p>
      <p class="hl-text">線は左から右へ伸びます。<mark class="hl">行をまたいで折り返す長い語句でも、線は途中で切れずに行ごとに引かれます</mark>。</p>
    </section>
    <section class="hl-block">
      <p class="dv-eyebrow">Section 3</p>
      <p class="hl-text">一つの文に<mark class="hl" style="--i: 0">印を付けたい語</mark>が<mark class="hl" style="--i: 1">いくつか</mark>あるときは、<mark class="hl" style="--i: 2">先に出てくる語</mark>から少しずつ遅れて引かれます。</p>
    </section>
    <section class="hl-block">
      <p class="dv-eyebrow">Section 4</p>
      <p class="hl-text">一度引いた線は、<mark class="hl">スクロールを戻しても消えません</mark>。読み返すときも、印はそのまま残ります。</p>
    </section>
    <section class="hl-block">
      <p class="dv-eyebrow">Section 5</p>
      <p class="hl-text">線の色は<mark class="hl" style="--i: 0">アクセントの一色だけ</mark>を薄く混ぜて使い、<mark class="hl" style="--i: 1">文字の色は変えません</mark>。</p>
    </section>
  </div>
</main>

<footer class="dv-end">END — 27 マーカー線</footer>

<script>
/* dv-motion-helpers:start */
const dvReduce = matchMedia('(prefers-reduced-motion: reduce)').matches;
document.documentElement.classList.add('js');

/**
 * 画面に入った要素へ .is-in を付ける。
 * data-reveal="repeat" の要素は画面を出たら外す（何度でも再生）。
 */
function dvReveal(selector = '[data-reveal]', { threshold = 0.2, rootMargin = '0px 0px -8% 0px' } = {}) {
  const els = [...document.querySelectorAll(selector)];
  if (dvReduce || !('IntersectionObserver' in window)) {
    els.forEach((el) => el.classList.add('is-in'));
    return;
  }
  const io = new IntersectionObserver((entries) => {
    for (const e of entries) {
      if (e.isIntersecting) {
        e.target.classList.add('is-in');
        if (e.target.dataset.reveal !== 'repeat') io.unobserve(e.target);
      } else if (e.target.dataset.reveal === 'repeat') {
        e.target.classList.remove('is-in');
      }
    }
  }, { threshold, rootMargin });
  els.forEach((el) => io.observe(el));
}

/**
 * スクロール量を 0〜1 にして、各 [data-progress] 要素の CSS 変数 --p に書く。
 *   data-progress="through" : 要素の上端が画面の下端に来たとき 0、下端が画面の上端を抜けたとき 1
 *   data-progress="pin"     : 要素の上端が画面の上端に来たとき 0、下端が画面の下端に来たとき 1
 *                             （中に position: sticky の箱を持つ、背の高い区画用）
 *   data-progress="page"    : ページ全体のスクロール量
 * onUpdate(el, p) を渡すと、値が変わるたびに呼ばれる。
 */
function dvProgress(onUpdate) {
  const els = [...document.querySelectorAll('[data-progress]')];
  const clamp = (n) => Math.min(1, Math.max(0, n));
  let queued = false;
  const measure = () => {
    queued = false;
    const vh = window.innerHeight;
    for (const el of els) {
      const r = el.getBoundingClientRect();
      let p;
      if (el.dataset.progress === 'pin') p = r.height > vh ? -r.top / (r.height - vh) : 0;
      else if (el.dataset.progress === 'page') {
        const max = document.documentElement.scrollHeight - vh;
        p = max > 0 ? window.scrollY / max : 0;
      } else p = (vh - r.top) / (vh + r.height);
      p = clamp(p);
      el.style.setProperty('--p', p.toFixed(4));
      if (onUpdate) onUpdate(el, p);
    }
  };
  const request = () => {
    if (!queued) { queued = true; requestAnimationFrame(measure); }
  };
  addEventListener('scroll', request, { passive: true });
  addEventListener('resize', request);
  measure();
}
/* dv-motion-helpers:end */

/* ---- この演出だけの JS ---- */
// 語そのものを見張る。画面の下端から 2 割ほど上まで入ったところで線を引き始める。
dvReveal('.hl', { threshold: 0.6, rootMargin: '0px 0px -20% 0px' });
</script>
</body>
</html>

/ai/assets/motion-highlighter-sweep.json