04Card Whose Focus Loosens and Locks With the Range Value

<main class="stage">
<div class="bfs is-demo" id="bfsRoot">
  <div class="bfs__badge" id="bfsBadge">cover range 0%~100%</div>
  <button class="bfs__ctrl" id="bfsCtrl" type="button">Pause</button>
  <div class="bfs__view" id="bfsView">
    <div class="bfs__track" id="bfsTrack">
      <div class="bfs__spacer bfs__spacer--top"></div>
      <div class="bfs__card" id="bfsCard">
        <span class="bfs__label">Product</span>
      </div>
      <div class="bfs__spacer bfs__spacer--bottom"></div>
    </div>
  </div>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 핵심: animation-timeline: view() + animation-range: cover 로 요소가 뷰포트를
// 통과하는 전체 구간 값(0~1)에 흐림 정도를 묶는다 — 시작·끝에서 흐리고 중간에서
// 또렷해진다(초점이 풀렸다 맞는다). 미지원 환경은 스크롤 위치로 같은 통과 진행 값을
// 직접 계산해 동일한 흐림 값을 그린다.

$duration: $dur-loop;
$easing: linear;
$color: $subject-blue-deep;

@include stage($stage-paper);

.bfs {
  position: relative;
  width: min(100%, 280px);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-3;
}

.bfs__badge {
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(20, 45, 120, .08);
  color: $subject-blue-deep;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.bfs__ctrl {
  position: absolute;
  top: 0;
  right: 0;
  border: 0;
  border-radius: $r-xs;
  padding: $sp-1 $sp-2;
  background: rgba(20, 45, 120, .10);
  color: $subject-blue-deep;
  font-weight: 600;
  font-size: 10px;
  line-height: 1.4;
  cursor: pointer;
}
.bfs__ctrl:focus-visible { outline: 2px solid $subject-blue-deep; outline-offset: 2px; }

.bfs__view {
  box-sizing: border-box;
  width: 100%;
  height: 176px;
  overflow-y: auto;
  overflow-x: hidden;
  border-radius: $r-card;
  background: rgba(20, 45, 120, .05);
  scrollbar-width: thin;
}

.bfs__track {
  display: flex;
  flex-direction: column;
  align-items: center;
}

.bfs__spacer--top { height: 200px; flex: 0 0 auto; }
.bfs__spacer--bottom { height: 200px; flex: 0 0 auto; }

.bfs__card {
  flex: 0 0 auto;
  box-sizing: border-box;
  width: 200px;
  height: 84px;
  display: grid;
  place-items: center;
  border-radius: $r-card;
  background: $color;
  box-shadow: $shadow-raised;
  filter: blur(var(--blur-max, 12px));
}

.bfs__label {
  color: $subject-cream;
  font-weight: 700;
  font-size: 14px;
}

.supports-vt .bfs__card {
  animation-name: bfsFocus;
  animation-duration: 1s;
  animation-timing-function: linear;
  animation-fill-mode: both;
  animation-timeline: view();
  animation-range: cover;
}
@keyframes bfsFocus {
  0%   { filter: blur(var(--blur-max, 12px)); opacity: .55; }
  50%  { filter: blur(0px); opacity: 1; }
  100% { filter: blur(var(--blur-max, 12px)); opacity: .55; }
}

@media (max-width: 340px) {
  .bfs { gap: $sp-2; }
  .bfs__view { height: 130px; }
  .bfs__spacer--top { height: 150px; }
  .bfs__spacer--bottom { height: 150px; }
  .bfs__card { width: 168px; height: 68px; }
}

@media (prefers-reduced-motion: reduce) {
  .bfs__card { animation: none !important; filter: blur(0px) !important; opacity: 1 !important; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.bfs {
  position: relative;
  width: min(100%, 280px);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
}

.bfs__badge {
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(20, 45, 120, 0.08);
  color: #0a4fe8;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.bfs__ctrl {
  position: absolute;
  top: 0;
  right: 0;
  border: 0;
  border-radius: 4px;
  padding: 4px 8px;
  background: rgba(20, 45, 120, 0.1);
  color: #0a4fe8;
  font-weight: 600;
  font-size: 10px;
  line-height: 1.4;
  cursor: pointer;
}

.bfs__ctrl:focus-visible {
  outline: 2px solid #0a4fe8;
  outline-offset: 2px;
}

.bfs__view {
  box-sizing: border-box;
  width: 100%;
  height: 176px;
  overflow-y: auto;
  overflow-x: hidden;
  border-radius: 16px;
  background: rgba(20, 45, 120, 0.05);
  scrollbar-width: thin;
}

.bfs__track {
  display: flex;
  flex-direction: column;
  align-items: center;
}

.bfs__spacer--top {
  height: 200px;
  flex: 0 0 auto;
}

.bfs__spacer--bottom {
  height: 200px;
  flex: 0 0 auto;
}

.bfs__card {
  flex: 0 0 auto;
  box-sizing: border-box;
  width: 200px;
  height: 84px;
  display: grid;
  place-items: center;
  border-radius: 16px;
  background: #0a4fe8;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  filter: blur(var(--blur-max, 12px));
}

.bfs__label {
  color: #fff7e6;
  font-weight: 700;
  font-size: 14px;
}

.supports-vt .bfs__card {
  animation-name: bfsFocus;
  animation-duration: 1s;
  animation-timing-function: linear;
  animation-fill-mode: both;
  animation-timeline: view();
  animation-range: cover;
}

@keyframes bfsFocus {
  0% {
    filter: blur(var(--blur-max, 12px));
    opacity: 0.55;
  }
  50% {
    filter: blur(0px);
    opacity: 1;
  }
  100% {
    filter: blur(var(--blur-max, 12px));
    opacity: 0.55;
  }
}
@media (max-width: 340px) {
  .bfs {
    gap: 8px;
  }
  .bfs__view {
    height: 130px;
  }
  .bfs__spacer--top {
    height: 150px;
  }
  .bfs__spacer--bottom {
    height: 150px;
  }
  .bfs__card {
    width: 168px;
    height: 68px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .bfs__card {
    animation: none !important;
    filter: blur(0px) !important;
    opacity: 1 !important;
  }
}

(function () {
  // VIEWTL_BLUR_MAX_PX — 변형 2: 12 → 24 로 늘리면 들어오고 나갈 때 초점이 풀리는 정도가 더 뚜렷해진다.
  var VIEWTL_BLUR_MAX_PX = 12;
  document.documentElement.style.setProperty('--blur-max', VIEWTL_BLUR_MAX_PX + 'px');

  var supportsVt = CSS.supports('animation-timeline: view()');
  var root = document.getElementById('bfsRoot');
  var view = document.getElementById('bfsView');
  var card = document.getElementById('bfsCard');
  var badge = document.getElementById('bfsBadge');
  var ctrl = document.getElementById('bfsCtrl');
  root.classList.add(supportsVt ? 'supports-vt' : 'no-vt');

  // 계산 한 겹: 요소가 뷰포트를 완전히 통과하는 구간(cover) 진행 값을 요소 높이·뷰포트
  // 높이·스크롤 위치로 직접 계산한다 (교차 비율이 아니라 통과 위치 값).
  function coverProgress() {
    var elTop = card.offsetTop;
    var elH = card.offsetHeight;
    var viewH = view.clientHeight;
    var raw = (view.scrollTop - elTop + viewH) / (elH + viewH);
    return Math.min(1, Math.max(0, raw));
  }

  function render(cov) {
    var hump = 1 - Math.abs(cov * 2 - 1);
    var blurPx = VIEWTL_BLUR_MAX_PX * (1 - hump);
    if (!supportsVt) {
      card.style.filter = 'blur(' + blurPx.toFixed(1) + 'px)';
      card.style.opacity = String(0.55 + 0.45 * hump);
    }
    badge.textContent = 'cover progress ' + Math.round(cov * 100) + '% · blur ' + blurPx.toFixed(1) + 'px';
  }

  view.addEventListener('scroll', function () {
    render(coverProgress());
  }, { passive: true });
  render(coverProgress());

  // 자동 시연: rAF 로 프레임을 누적해 컨테이너를 왕복 스크롤한다.
  var playing = true;
  var frame = 0;
  var PERIOD = 80;
  function tick() {
    if (playing) {
      frame += 1;
      var max = view.scrollHeight - view.clientHeight;
      var t = frame % (PERIOD * 2);
      var f = t < PERIOD ? (t / PERIOD) : ((PERIOD * 2 - t) / PERIOD);
      view.scrollTop = f * max;
      render(coverProgress());
    }
    requestAnimationFrame(tick);
  }
  requestAnimationFrame(tick);

  function stopAuto() {
    if (root.classList.contains('is-demo')) { root.classList.remove('is-demo'); }
    playing = false;
    ctrl.textContent = 'Play';
  }
  view.addEventListener('wheel', stopAuto, { passive: true });
  view.addEventListener('touchstart', stopAuto, { passive: true });

  ctrl.addEventListener('click', function () {
    playing = !playing;
    ctrl.textContent = playing ? 'Pause' : 'Play';
    if (playing) { root.classList.add('is-demo'); }
    render(coverProgress());
  });
  ctrl.addEventListener('keydown', function (e) {
    if (e.key === 'r' || e.key === 'R') {
      frame = 0;
      view.scrollTop = 0;
      playing = true;
      root.classList.add('is-demo');
      ctrl.textContent = 'Pause';
      render(coverProgress());
    }
  });

  window.addEventListener('resize', function () {
    render(coverProgress());
  });

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (reduce) {
    playing = false;
    root.classList.remove('is-demo');
    card.style.filter = 'blur(0px)';
    card.style.opacity = '1';
    badge.textContent = 'cover progress 50% · blur 0.0px';
  }
})();

import { useEffect, useRef, useState } from "react";
import styles from "./BlurFocusStack.module.scss";

// 핵심: animation-timeline: view() + animation-range: cover 로 요소가 뷰포트를
// 통과하는 전체 구간 값(0~1)에 흐림 정도를 묶는다 — 시작·끝에서 흐리고 중간에서
// 또렷해진다. 미지원 환경은 스크롤 위치로 같은 통과 진행 값을 직접 계산한다.
// VIEWTL_BLUR_MAX_PX — 변형 2: 12 → 24 로 늘리면 흐려지는 정도가 더 뚜렷해진다.
const VIEWTL_BLUR_MAX_PX = 12;

export default function BlurFocusStack() {
  const rootRef = useRef<HTMLDivElement>(null);
  const viewRef = useRef<HTMLDivElement>(null);
  const cardRef = useRef<HTMLDivElement>(null);
  const [badge, setBadge] = useState("통과 구간 0%~100%");
  const [demo, setDemo] = useState(true);
  const [supportsVt, setSupportsVt] = useState(false);

  useEffect(() => {
    const view = viewRef.current;
    const card = cardRef.current;
    const root = rootRef.current;
    if (!view || !card || !root) { return; }

    card.style.setProperty("--blur-max", VIEWTL_BLUR_MAX_PX + "px");
    const vt = CSS.supports("animation-timeline: view()");
    setSupportsVt(vt);

    function coverProgress() {
      const elTop = card!.offsetTop;
      const elH = card!.offsetHeight;
      const viewH = view!.clientHeight;
      const raw = (view!.scrollTop - elTop + viewH) / (elH + viewH);
      return Math.min(1, Math.max(0, raw));
    }

    function render(cov: number) {
      const hump = 1 - Math.abs(cov * 2 - 1);
      const blurPx = VIEWTL_BLUR_MAX_PX * (1 - hump);
      if (!vt) {
        card!.style.filter = "blur(" + blurPx.toFixed(1) + "px)";
        card!.style.opacity = String(0.55 + 0.45 * hump);
      }
      setBadge("통과 진행 " + Math.round(cov * 100) + "% · 흐림 " + blurPx.toFixed(1) + "px");
    }

    function onScroll() { render(coverProgress()); }
    view.addEventListener("scroll", onScroll, { passive: true });
    render(coverProgress());

    let playing = true;
    let frame = 0;
    const PERIOD = 80;
    let rafId = 0;
    function tick() {
      if (playing) {
        frame += 1;
        const max = view!.scrollHeight - view!.clientHeight;
        const t = frame % (PERIOD * 2);
        const f = t < PERIOD ? (t / PERIOD) : ((PERIOD * 2 - t) / PERIOD);
        view!.scrollTop = f * max;
        render(coverProgress());
      }
      rafId = requestAnimationFrame(tick);
    }
    rafId = requestAnimationFrame(tick);

    function stopAuto() {
      setDemo(false);
      playing = false;
    }
    view.addEventListener("wheel", stopAuto, { passive: true });
    view.addEventListener("touchstart", stopAuto, { passive: true });

    function onClick() {
      playing = !playing;
      setDemo(playing);
      render(coverProgress());
    }
    function onKeyDown(e: KeyboardEvent) {
      if (e.key === "r" || e.key === "R") {
        frame = 0;
        view!.scrollTop = 0;
        playing = true;
        setDemo(true);
        render(coverProgress());
      }
    }
    root.addEventListener("keydown", onKeyDown);

    function onResize() { render(coverProgress()); }
    window.addEventListener("resize", onResize);

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (reduce) {
      playing = false;
      setDemo(false);
      card.style.filter = "blur(0px)";
      card.style.opacity = "1";
      setBadge("통과 진행 50% · 흐림 0.0px");
    }

    const ctrl = root.querySelector("button");
    ctrl?.addEventListener("click", onClick);

    return () => {
      cancelAnimationFrame(rafId);
      view.removeEventListener("scroll", onScroll);
      view.removeEventListener("wheel", stopAuto);
      view.removeEventListener("touchstart", stopAuto);
      root.removeEventListener("keydown", onKeyDown);
      window.removeEventListener("resize", onResize);
      ctrl?.removeEventListener("click", onClick);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <div ref={rootRef} className={`${styles.bfs} ${demo ? styles["is-demo"] : ""} ${supportsVt ? styles["supports-vt"] : styles["no-vt"]}`}>
        <div className={styles["bfs__badge"]}>{badge}</div>
        <button className={styles["bfs__ctrl"]} type="button">{demo ? "일시정지" : "재생"}</button>
        <div ref={viewRef} className={styles["bfs__view"]}>
          <div className={styles["bfs__track"]}>
            <div className={`${styles["bfs__spacer"]} ${styles["bfs__spacer--top"]}`} />
            <div ref={cardRef} className={styles["bfs__card"]}>
              <span className={styles["bfs__label"]}>제품</span>
            </div>
            <div className={`${styles["bfs__spacer"]} ${styles["bfs__spacer--bottom"]}`} />
          </div>
        </div>
      </div>
    </main>
  );
}