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11 Scale on scroll

Motion · Scroll-linked
Scale on scroll

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motion-scroll-zoom-everything.md

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Prompt

860 B
Scale on scroll — Scale on scroll

An image appears at half the screen size and expands to full screen as the user scrolls. Make the section 300vh tall and the box that holds the image a 100vh sticky element.
Use `scale(calc(0.5 + var(--p) * 0.5))` for the scale, and `calc((1 - var(--p)) * 32px)` for the corner radius so the corners reach 0 when --p is 1.
Place one paragraph of text before and after the image, so the next paragraph appears only after the zoom has finished.
Implement with CSS and plain JavaScript only; do not use a library.

Do not drop:
- The zoom completes inside the pinned section; the box stays fixed on screen
- Scale stays between 0.5 and 1
- With reduced motion, show the full-screen end state without scaling

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

Files

demo.html

7.6 KB

/designs/motion-scroll-zoom/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>11 スクロールズーム — Scale on scroll</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 ---- */
.stack { display: grid; gap: var(--s6); }
.zoom { height: 300vh; }
.zoom-stick { position: sticky; top: 0; height: 100vh; overflow: hidden; }
.zoom-img {
  position: absolute; inset: 0;
  display: grid; place-items: center;
  background: linear-gradient(135deg, var(--accent-soft), var(--accent-mid) 60%, var(--accent));
  transform: scale(calc(0.5 + var(--p) * 0.5));
  border-radius: calc((1 - var(--p)) * 32px);
}
.zoom-cap { font-size: var(--t-h2); font-weight: 700; color: var(--ground); }

@media (prefers-reduced-motion: reduce) {
  .zoom-img { transform: none; border-radius: 0; }
}
</style>
</head>
<body data-motion-number="11">
<header class="dv-label">
  <div class="dv-wrap">
    <p class="dv-num">11</p>
    <h1 class="dv-name">スクロールズーム</h1>
    <p class="dv-ai">Scale on scroll</p>
    <p class="dv-desc">画像が拡大して全画面に</p>
    <p class="dv-hint">SCROLL ↓</p>
  </div>
</header>

<main class="dv-stage">
  <div class="dv-wrap stack">
    <section class="dv-card">
      <p class="dv-eyebrow">Section 1</p>
      <h2 class="dv-h2">見出しが入ります</h2>
      <p class="dv-lead">本文のダミーです。スクロールすると、下の画像が画面の半分の大きさから広がります。</p>
    </section>
  </div>

  <section class="zoom" data-progress="pin">
    <div class="zoom-stick">
      <div class="zoom-img"><p class="zoom-cap">見出しが入ります</p></div>
    </div>
  </section>

  <div class="dv-wrap stack">
    <section class="dv-card">
      <p class="dv-eyebrow">Section 2</p>
      <h2 class="dv-h2">見出しが入ります</h2>
      <p class="dv-lead">本文のダミーです。拡大が終わったあとに、この段落が続きます。</p>
    </section>
  </div>
</main>

<footer class="dv-end">END — 11 スクロールズーム</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 ---- */
dvProgress();
</script>
</body>
</html>

/ai/assets/motion-scroll-zoom.json