{
  "id": "motion:motion-velocity-skew",
  "slug": "motion-velocity-skew",
  "kind": "motion",
  "title": {
    "ja": "ベロシティスキュー",
    "en": "Velocity skew"
  },
  "aiName": "Scroll-velocity skew",
  "summary": {
    "ja": "速くスクロールすると傾く",
    "en": "Headings tilt when you scroll fast and level out when you stop"
  },
  "number": 40,
  "group": "ambient",
  "techniques": [
    "scroll-velocity"
  ],
  "rules": [
    {
      "ja": "傾きは ±6 度で頭打ちにし、どれほど速くても崩れない",
      "en": "The tilt is capped at ±6 degrees, however fast the scroll"
    },
    {
      "ja": "止まったら傾きは減衰して 0 に戻り、静止時に傾いたまま残らない",
      "en": "When scrolling stops the tilt decays back to 0 and never stays tilted at rest"
    },
    {
      "ja": "動きを減らす設定では傾けず、計測の処理も始めない",
      "en": "With reduced motion, nothing tilts and no measuring loop starts"
    }
  ],
  "reproduction": {
    "prompt": {
      "ja": "ベロシティスキュー — Scroll-velocity skew\n\n見出しの群を、スクロール速度に応じて斜めに傾ける。requestAnimationFrame で 1 フレームあたりのスクロール量を測り、速度 v に 0.02 を掛けて `skewY(clamp(-6deg, v * 0.02, 6deg))` の値にする。v は 60Hz の 1 フレームを基準に正規化し、画面の更新頻度が違っても傾きが変わらないようにする。\nスクロールが止まると v を 1 フレームごとに 0.9 倍へ減衰させ、傾きは数分の 1 秒で 0 に戻る。傾けるのは見出しと本文を含む 5 つの区画で、各区画は 80vh の高さを持つ。\nCSS 変数 `--skew` を経由して `transform` だけを書き換え、ライブラリは使わない。\n\n外すと崩れる点:\n- 傾きは ±6 度で頭打ちにし、どれほど速くても崩れない\n- 止まったら傾きは減衰して 0 に戻り、静止時に傾いたまま残らない\n- 動きを減らす設定では傾けず、計測の処理も始めない\n\n動く実物（1 ファイルで完結する HTML）: https://design-vault.pages.dev/designs/motion-velocity-skew/demo.html",
      "en": "Velocity skew — Scroll-velocity skew\n\nTilt groups of headings according to scroll speed. Measure the scroll amount per animation frame with requestAnimationFrame, multiply the velocity v by 0.02 and apply `skewY(clamp(-6deg, v * 0.02, 6deg))`. Normalise v to a 60 Hz frame so that the tilt does not change with screen refresh rate.\nWhen scrolling stops, multiply v by 0.9 each frame so the tilt returns to 0 within a fraction of a second. Tilt five sections, each 80vh tall, containing headings and body text.\nWrite only `transform`, through a CSS variable `--skew`; do not use a library.\n\nDo not drop:\n- The tilt is capped at ±6 degrees, however fast the scroll\n- When scrolling stops the tilt decays back to 0 and never stays tilted at rest\n- With reduced motion, nothing tilts and no measuring loop starts\n\nA working example (one self-contained HTML file): https://design-vault.pages.dev/designs/motion-velocity-skew/demo.html"
    },
    "code": {
      "url": "https://design-vault.pages.dev/designs/motion-velocity-skew/demo.html",
      "html": "<!doctype html>\n<html lang=\"ja\">\n<head>\n<meta charset=\"utf-8\">\n<meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">\n<title>40 ベロシティスキュー — Scroll-velocity skew</title>\n<style>\n/* dv-motion-base:start */\n:root {\n  --ground: #FFFFFF;\n  --surface: #F3F5F8;\n  --ink: #14181F;\n  --muted: #5A6472;\n  --accent: #1F5FA8;\n  --rule: #D8DDE4;\n  --accent-soft: color-mix(in srgb, var(--accent) 12%, var(--ground));\n  --accent-mid: color-mix(in srgb, var(--accent) 45%, var(--ground));\n  --shade: color-mix(in srgb, var(--ink) 14%, transparent);\n\n  --font: \"Zen Kaku Gothic New\", \"Hiragino Sans\", \"Noto Sans JP\", \"Yu Gothic\", system-ui, sans-serif;\n  --mono: ui-monospace, \"SF Mono\", Menlo, Consolas, monospace;\n\n  --t-label: 13px;\n  --t-body: 16px;\n  --t-lead: 20px;\n  --t-h2: 32px;\n  --t-h1: clamp(40px, 7vw, 72px);\n\n  --s1: 4px;\n  --s2: 8px;\n  --s3: 16px;\n  --s4: 24px;\n  --s5: 40px;\n  --s6: 64px;\n  --s7: 104px;\n\n  --radius: 12px;\n  --ease: cubic-bezier(.2, .7, .2, 1);\n  --dur: .7s;\n  --measure: 1080px;\n}\n*, *::before, *::after { box-sizing: border-box; }\nhtml { -webkit-text-size-adjust: 100%; }\nbody {\n  margin: 0;\n  background: var(--ground);\n  color: var(--ink);\n  font-family: var(--font);\n  font-size: var(--t-body);\n  line-height: 1.7;\n  font-feature-settings: \"palt\";\n  overflow-x: hidden;\n}\nh1, h2, h3, p, ul, ol, figure { margin: 0; padding: 0; }\nul, ol { list-style: none; }\n.dv-wrap { width: min(100% - 2 * var(--s4), var(--measure)); margin-inline: auto; }\n.dv-label {\n  min-height: 72vh;\n  display: grid;\n  align-content: center;\n  gap: var(--s3);\n  padding-block: var(--s6);\n  border-bottom: 1px solid var(--rule);\n}\n.dv-num { font-family: var(--mono); font-size: var(--t-lead); font-weight: 700; color: var(--accent); letter-spacing: .04em; }\n.dv-name { font-size: var(--t-h1); font-weight: 700; line-height: 1.15; letter-spacing: .01em; }\n.dv-ai { font-family: var(--mono); font-size: var(--t-lead); color: var(--muted); }\n.dv-desc { font-size: var(--t-lead); color: var(--ink); }\n.dv-hint { font-size: var(--t-label); color: var(--muted); letter-spacing: .12em; margin-top: var(--s4); }\n.dv-stage { padding-block: var(--s7); }\n.dv-h2 { font-size: var(--t-h2); font-weight: 700; line-height: 1.3; }\n.dv-lead { font-size: var(--t-lead); color: var(--muted); }\n.dv-eyebrow { font-family: var(--mono); font-size: var(--t-label); color: var(--accent); letter-spacing: .12em; text-transform: uppercase; }\n.dv-card { background: var(--surface); border: 1px solid var(--rule); border-radius: var(--radius); padding: var(--s4); }\n.dv-ph {\n  border-radius: var(--radius);\n  background: linear-gradient(135deg, var(--accent-soft), var(--accent-mid) 60%, var(--accent));\n  aspect-ratio: 16 / 9;\n}\n.dv-ph--alt { background: linear-gradient(200deg, var(--surface), var(--accent-soft) 55%, var(--accent-mid)); }\n.dv-ph--ink { background: linear-gradient(160deg, var(--ink), color-mix(in srgb, var(--ink) 55%, var(--accent))); }\n.dv-end {\n  min-height: 60vh;\n  display: grid;\n  place-items: center;\n  border-top: 1px solid var(--rule);\n  color: var(--muted);\n  font-family: var(--mono);\n  font-size: var(--t-label);\n  letter-spacing: .12em;\n}\n/* dv-motion-base:end */\n\n/* ---- この演出だけの CSS。色は var(--…) か color-mix() のみ ---- */\n.stack { display: grid; gap: var(--s7); }\n.vs-block { min-height: 80vh; display: grid; align-content: center; }\n.vs-group { transform: skewY(var(--skew, 0deg)); transform-origin: 0 50%; will-change: transform; }\n.vs-tag { font-family: var(--mono); font-size: var(--t-label); color: var(--accent); letter-spacing: .12em; }\n\n@media (prefers-reduced-motion: reduce) {\n  .vs-group { transform: none; }\n}\n</style>\n</head>\n<body data-motion-number=\"40\">\n<header class=\"dv-label\">\n  <div class=\"dv-wrap\">\n    <p class=\"dv-num\">40</p>\n    <h1 class=\"dv-name\">ベロシティスキュー</h1>\n    <p class=\"dv-ai\">Scroll-velocity skew</p>\n    <p class=\"dv-desc\">速くスクロールすると傾く</p>\n    <p class=\"dv-hint\">SCROLL ↓</p>\n  </div>\n</header>\n\n<main class=\"dv-stage\">\n  <div class=\"dv-wrap stack\">\n    <section class=\"vs-block\">\n      <div class=\"vs-group\">\n        <p class=\"vs-tag\">Section 1</p>\n        <h2 class=\"dv-h2\">見出しが入ります</h2>\n        <p class=\"dv-lead\">本文のダミーです。速くスクロールすると、見出しの群が傾きます。</p>\n      </div>\n    </section>\n    <section class=\"vs-block\">\n      <div class=\"vs-group\">\n        <p class=\"vs-tag\">Section 2</p>\n        <h2 class=\"dv-h2\">見出しが入ります</h2>\n        <p class=\"dv-lead\">本文のダミーです。止めると、傾きは減衰して 0 に戻ります。</p>\n      </div>\n    </section>\n    <section class=\"vs-block\">\n      <div class=\"vs-group\">\n        <p class=\"vs-tag\">Section 3</p>\n        <h2 class=\"dv-h2\">見出しが入ります</h2>\n        <div class=\"dv-ph\"></div>\n      </div>\n    </section>\n    <section class=\"vs-block\">\n      <div class=\"vs-group\">\n        <p class=\"vs-tag\">Section 4</p>\n        <h2 class=\"dv-h2\">見出しが入ります</h2>\n        <p class=\"dv-lead\">本文のダミーです。動きを減らす設定では、傾かずに静止したままです。</p>\n      </div>\n    </section>\n    <section class=\"vs-block\">\n      <div class=\"vs-group\">\n        <p class=\"vs-tag\">Section 5</p>\n        <h2 class=\"dv-h2\">見出しが入ります</h2>\n        <div class=\"dv-ph dv-ph--alt\"></div>\n      </div>\n    </section>\n  </div>\n</main>\n\n<footer class=\"dv-end\">END — 40 ベロシティスキュー</footer>\n\n<script>\n/* dv-motion-helpers:start */\nconst dvReduce = matchMedia('(prefers-reduced-motion: reduce)').matches;\ndocument.documentElement.classList.add('js');\n\n/**\n * 画面に入った要素へ .is-in を付ける。\n * data-reveal=\"repeat\" の要素は画面を出たら外す（何度でも再生）。\n */\nfunction dvReveal(selector = '[data-reveal]', { threshold = 0.2, rootMargin = '0px 0px -8% 0px' } = {}) {\n  const els = [...document.querySelectorAll(selector)];\n  if (dvReduce || !('IntersectionObserver' in window)) {\n    els.forEach((el) => el.classList.add('is-in'));\n    return;\n  }\n  const io = new IntersectionObserver((entries) => {\n    for (const e of entries) {\n      if (e.isIntersecting) {\n        e.target.classList.add('is-in');\n        if (e.target.dataset.reveal !== 'repeat') io.unobserve(e.target);\n      } else if (e.target.dataset.reveal === 'repeat') {\n        e.target.classList.remove('is-in');\n      }\n    }\n  }, { threshold, rootMargin });\n  els.forEach((el) => io.observe(el));\n}\n\n/**\n * 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。\n *   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\n *   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\n *                             （中に position: sticky の箱を持つ、背の高い区画用）\n *   data-progress=\"page\"    : ページ全体のスクロール量\n * onUpdate(el, p) を渡すと、値が変わるたびに呼ばれる。\n */\nfunction dvProgress(onUpdate) {\n  const els = [...document.querySelectorAll('[data-progress]')];\n  const clamp = (n) => Math.min(1, Math.max(0, n));\n  let queued = false;\n  const measure = () => {\n    queued = false;\n    const vh = window.innerHeight;\n    for (const el of els) {\n      const r = el.getBoundingClientRect();\n      let p;\n      if (el.dataset.progress === 'pin') p = r.height > vh ? -r.top / (r.height - vh) : 0;\n      else if (el.dataset.progress === 'page') {\n        const max = document.documentElement.scrollHeight - vh;\n        p = max > 0 ? window.scrollY / max : 0;\n      } else p = (vh - r.top) / (vh + r.height);\n      p = clamp(p);\n      el.style.setProperty('--p', p.toFixed(4));\n      if (onUpdate) onUpdate(el, p);\n    }\n  };\n  const request = () => {\n    if (!queued) { queued = true; requestAnimationFrame(measure); }\n  };\n  addEventListener('scroll', request, { passive: true });\n  addEventListener('resize', request);\n  measure();\n}\n/* dv-motion-helpers:end */\n\n/* ---- この演出だけの JS ---- */\n// スクロール速度（60Hz の 1 フレームあたりの px）を測り、減衰させながら\n// 見出し群の --skew に写す。止まれば 0 に戻る。動きを減らす設定では動かさない。\nif (!dvReduce) {\n  const groups = [...document.querySelectorAll('.vs-group')];\n  const clamp = (n, lo, hi) => Math.min(hi, Math.max(lo, n));\n  const decay = 0.9;\n  let lastY = scrollY;\n  let lastT = 0;\n  let v = 0;\n  let running = false;\n\n  const frame = (now) => {\n    const dt = lastT ? Math.min(now - lastT, 100) : 16.67;\n    lastT = now;\n    const dy = scrollY - lastY;\n    lastY = scrollY;\n    v = dy !== 0 ? (dy / dt) * 16.67 : v * Math.pow(decay, dt / 16.67);\n    const skew = clamp(v * 0.02, -6, 6);\n    for (const el of groups) el.style.setProperty('--skew', skew.toFixed(3) + 'deg');\n    if (Math.abs(v) > 0.01) {\n      requestAnimationFrame(frame);\n    } else {\n      v = 0;\n      running = false;\n      lastT = 0;\n      for (const el of groups) el.style.setProperty('--skew', '0deg');\n    }\n  };\n  // lastY はここでは更新しない。scroll イベントは同じフレームの rAF の直前に来るので、\n  // ここで scrollY を写すと frame の差分が 0 になり、速さが一度も測れない。\n  const start = () => {\n    if (running) return;\n    running = true;\n    requestAnimationFrame(frame);\n  };\n  addEventListener('scroll', start, { passive: true });\n}\n</script>\n</body>\n</html>\n"
    }
  },
  "license": "Original",
  "catalogVersion": 1,
  "designSchemaVersion": 2,
  "capabilities": [
    "live-preview",
    "copy-prompt",
    "get-code"
  ],
  "reusePolicy": "construction-reuse",
  "urls": {
    "ja": "https://design-vault.pages.dev/designs/motion-velocity-skew",
    "en": "https://design-vault.pages.dev/en/designs/motion-velocity-skew",
    "json": "https://design-vault.pages.dev/ai/assets/motion-velocity-skew.json",
    "designJson": null
  }
}