05Crossfade Panel a Progress Value Blurs Then Clears

<main class="stage">
<div class="bf is-demo" id="bf">
  <div class="bf__tabs" role="tablist" aria-label="Category tabs">
    <button type="button" class="bf__tab is-active" role="tab" id="bf-tab-0" aria-selected="true" aria-controls="bf-panel-0" data-idx="0">Notices</button>
    <button type="button" class="bf__tab" role="tab" id="bf-tab-1" aria-selected="false" aria-controls="bf-panel-1" data-idx="1" tabindex="-1">Reviews</button>
    <button type="button" class="bf__tab" role="tab" id="bf-tab-2" aria-selected="false" aria-controls="bf-panel-2" data-idx="2" tabindex="-1">Records</button>
  </div>
  <div class="bf__wrap" id="bfWrap">
    <div class="bf__panel is-front" id="bf-panel-0" role="tabpanel" aria-labelledby="bf-tab-0" tabindex="0"><span class="bf__num">03</span><p class="bf__line">3 notices this week</p></div>
    <div class="bf__panel" id="bf-panel-1" role="tabpanel" aria-labelledby="bf-tab-1" tabindex="0" hidden><span class="bf__num">128</span><p class="bf__line">128 cumulative reviews</p></div>
    <div class="bf__panel" id="bf-panel-2" role="tabpanel" aria-labelledby="bf-tab-2" tabindex="0" hidden><span class="bf__num">47</span><p class="bf__line">47 recent records</p></div>
  </div>
  <p class="bf__meta">Transition progress t=<b id="bfT">0.00</b></p>
</div>
</main>

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

// 계산 겹: index.html 의 frame() 이 rAF 로 실측 경과시간/총시간 = t(0~1) 를 구해 setT() 에 넘긴다.
// 나가는 패널은 blur(t*BLUR_MAX)·opacity(1-t), 들어오는 패널은 blur((1-t)*BLUR_MAX)·opacity(t) —
// 두 패널이 초점이 옮겨가듯 겹쳐 지나간다. transition 없이 매 프레임 직접 스타일을 쓴다(진짜 t 계산).
@include stage($stage-ink);

.bf { width: min(100%, 300px); display: flex; flex-direction: column; gap: $sp-3; }
.bf__tabs { display: flex; gap: $sp-1; background: rgba($subject-cream, .12); padding: $sp-1; border-radius: $r-pill; }
.bf__tab {
  flex: 1 1 0; border: none; background: transparent; border-radius: $r-pill; cursor: pointer;
  padding: $sp-2 $sp-2; font-size: 11px; font-weight: 700; color: rgba($subject-cream, .72);
}
.bf__tab.is-active { background: $subject-blue-deep; color: $subject-cream; }
.bf__tab:focus-visible { outline: 2px solid $subject-cream; outline-offset: 2px; }

.bf__wrap { position: relative; min-width: 0; height: 140px; border-radius: $r-card; background: $subject-cream; overflow: hidden; }
.bf__panel {
  position: absolute; inset: 0; box-sizing: border-box; padding: $sp-4;
  display: flex; flex-direction: column; align-items: center; justify-content: center; gap: $sp-2;
  opacity: 0;
}
.bf__panel.is-front { z-index: 2; }
.bf__num { font-size: 32px; font-weight: 800; color: $subject-blue-deep; }
.bf__line { margin: 0; font-size: 12px; color: rgba($subject-ink, .72); }

.bf__meta { margin: 0; font-size: 11px; color: rgba($subject-cream, .78); text-align: center; }
.bf__meta b { color: $subject-cream; font-weight: 700; }

@media (max-width: 340px) {
  .bf { width: 100%; gap: $sp-2; }
  .bf__tab { padding: $sp-1 $sp-2; }
  .bf__wrap { height: 96px; }
  .bf__num { font-size: 26px; }
}

@media (prefers-reduced-motion: reduce) {
  .bf__panel { transition: none; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.bf {
  width: min(100%, 300px);
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.bf__tabs {
  display: flex;
  gap: 4px;
  background: rgba(255, 247, 230, 0.12);
  padding: 4px;
  border-radius: 999px;
}

.bf__tab {
  flex: 1 1 0;
  border: none;
  background: transparent;
  border-radius: 999px;
  cursor: pointer;
  padding: 8px 8px;
  font-size: 11px;
  font-weight: 700;
  color: rgba(255, 247, 230, 0.72);
}

.bf__tab.is-active {
  background: #0a4fe8;
  color: #fff7e6;
}

.bf__tab:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 2px;
}

.bf__wrap {
  position: relative;
  min-width: 0;
  height: 140px;
  border-radius: 16px;
  background: #fff7e6;
  overflow: hidden;
}

.bf__panel {
  position: absolute;
  inset: 0;
  box-sizing: border-box;
  padding: 16px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 8px;
  opacity: 0;
}

.bf__panel.is-front {
  z-index: 2;
}

.bf__num {
  font-size: 32px;
  font-weight: 800;
  color: #0a4fe8;
}

.bf__line {
  margin: 0;
  font-size: 12px;
  color: rgba(23, 20, 26, 0.72);
}

.bf__meta {
  margin: 0;
  font-size: 11px;
  color: rgba(255, 247, 230, 0.78);
  text-align: center;
}

.bf__meta b {
  color: #fff7e6;
  font-weight: 700;
}

@media (max-width: 340px) {
  .bf {
    width: 100%;
    gap: 8px;
  }
  .bf__tab {
    padding: 4px 8px;
  }
  .bf__wrap {
    height: 96px;
  }
  .bf__num {
    font-size: 26px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .bf__panel {
    transition: none;
  }
}

(function () {
  var BLUR_MAX = 10; // 계산 겹 상수: 진행률 t=1 에서 나가는 패널이 도달하는 최대 블러(px)
  var DUR_MS = 460;
  var HOLD_MS = 760;
  var COUNT = 3;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var root = document.getElementById('bf');
  var tEl = document.getElementById('bfT');
  var tabs = [0, 1, 2].map(function (i) { return document.getElementById('bf-tab-' + i); });
  var panels = [0, 1, 2].map(function (i) { return document.getElementById('bf-panel-' + i); });

  var isDemo = true;
  var active = 0;
  var raf = 0;

  function human() {
    if (isDemo) { root.classList.remove('is-demo'); isDemo = false; }
  }

  function setT(el, t, incoming) {
    // 계산 겹: 나가는 패널은 t 에 비례해 블러·투명도가 늘고, 들어오는 패널은 (1-t) 에 비례해 블러가 준다
    var blur = incoming ? (1 - t) * BLUR_MAX : t * BLUR_MAX;
    var opacity = incoming ? t : 1 - t;
    el.style.filter = 'blur(' + blur.toFixed(2) + 'px)';
    el.style.opacity = String(opacity);
  }

  function select(idx) {
    if (idx === active || raf) return;
    var prevIdx = active;
    var outEl = panels[prevIdx];
    var inEl = panels[idx];

    tabs[prevIdx].classList.remove('is-active');
    tabs[prevIdx].setAttribute('aria-selected', 'false');
    tabs[prevIdx].setAttribute('tabindex', '-1');
    tabs[idx].classList.add('is-active');
    tabs[idx].setAttribute('aria-selected', 'true');
    tabs[idx].setAttribute('tabindex', '0');

    inEl.removeAttribute('hidden');
    inEl.classList.add('is-front');
    setT(outEl, 0, false);
    setT(inEl, 0, true);

    var start = 0;
    function frame(ts) {
      if (!start) start = ts;
      var t = Math.min(1, (ts - start) / DUR_MS); // 계산 겹: 실측 경과시간 / 총 시간 = 진행률 t(0~1)
      setT(outEl, t, false);
      setT(inEl, t, true);
      tEl.textContent = t.toFixed(2);
      if (t < 1) {
        raf = requestAnimationFrame(frame);
      } else {
        raf = 0;
        outEl.setAttribute('hidden', '');
        outEl.classList.remove('is-front');
        active = idx;
      }
    }
    raf = requestAnimationFrame(frame);
  }

  tabs.forEach(function (t, i) {
    t.addEventListener('click', function () { human(); select(i); });
  });

  root.addEventListener('keydown', function (e) {
    var idx = tabs.indexOf(document.activeElement);
    if (idx === -1) return;
    var next = null;
    if (e.key === 'ArrowRight') next = (idx + 1) % COUNT;
    else if (e.key === 'ArrowLeft') next = (idx - 1 + COUNT) % COUNT;
    else if (e.key === 'Home') next = 0;
    else if (e.key === 'End') next = COUNT - 1;
    if (next === null) return;
    e.preventDefault();
    human();
    tabs[next].focus({ preventScroll: true });
    select(next);
  });

  function loop() {
    if (!isDemo) return;
    select((active + 1) % COUNT);
    window.setTimeout(loop, HOLD_MS);
  }

  if (!reduce) {
    window.setTimeout(loop, HOLD_MS);
  } else {
    root.classList.remove('is-demo');
  }
})();

// TabBlurFocusCrossfade — vanilla 판(run/394/demo/05-tab-panel-blur-focus-crossfade/index.html) 의 React 포트.
// select() 의 frame() 이 rAF 로 실측 경과시간/총시간 = t(0~1) 를 구해, 나가는 패널은 blur(t*BLUR_MAX)·
// opacity(1-t), 들어오는 패널은 blur((1-t)*BLUR_MAX)·opacity(t) 로 매 프레임 직접 스타일을 쓴다.
import { useEffect, useRef } from "react";
import styles from "./TabBlurFocusCrossfade.module.scss";

type Box<T> = { current: T };

const BLUR_MAX = 10; // 계산 겹 상수: 진행률 t=1 에서 나가는 패널이 도달하는 최대 블러(px)
const DUR_MS = 460;
const HOLD_MS = 760;
const COUNT = 3;

export default function TabBlurFocusCrossfade() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const tEl = useRef(null) as unknown as Box<HTMLElement>;
  const tabRefs = useRef([null, null, null]) as unknown as Box<(HTMLButtonElement | null)[]>;
  const panelRefs = useRef([null, null, null]) as unknown as Box<(HTMLDivElement | null)[]>;
  const timerRef = useRef(0) as unknown as Box<number>;
  const rafRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let isDemo = true;
    let active = 0;

    function human() {
      if (isDemo) { rootRef.current?.classList.remove(styles.isDemo); isDemo = false; }
    }

    function setT(el: HTMLElement, t: number, incoming: boolean) {
      const blur = incoming ? (1 - t) * BLUR_MAX : t * BLUR_MAX; // 계산 겹
      const opacity = incoming ? t : 1 - t;
      el.style.filter = "blur(" + blur.toFixed(2) + "px)";
      el.style.opacity = String(opacity);
    }

    function select(idx: number) {
      if (idx === active || rafRef.current) return;
      const prevIdx = active;
      const outEl = panelRefs.current[prevIdx];
      const inEl = panelRefs.current[idx];
      if (!outEl || !inEl) return;

      const prevTab = tabRefs.current[prevIdx], nextTab = tabRefs.current[idx];
      prevTab?.classList.remove(styles.isActive);
      prevTab?.setAttribute("aria-selected", "false");
      prevTab?.setAttribute("tabindex", "-1");
      nextTab?.classList.add(styles.isActive);
      nextTab?.setAttribute("aria-selected", "true");
      nextTab?.setAttribute("tabindex", "0");

      inEl.removeAttribute("hidden");
      inEl.classList.add(styles.isFront);
      setT(outEl, 0, false);
      setT(inEl, 0, true);

      let start = 0;
      function frame(ts: number) {
        if (!start) start = ts;
        const t = Math.min(1, (ts - start) / DUR_MS); // 계산 겹: 실측 경과시간 / 총 시간 = 진행률 t(0~1)
        setT(outEl!, t, false);
        setT(inEl!, t, true);
        if (tEl.current) tEl.current.textContent = t.toFixed(2);
        if (t < 1) {
          rafRef.current = requestAnimationFrame(frame);
        } else {
          rafRef.current = 0;
          outEl!.setAttribute("hidden", "");
          outEl!.classList.remove(styles.isFront);
          active = idx;
        }
      }
      rafRef.current = requestAnimationFrame(frame);
    }

    function onKeydown(e: KeyboardEvent) {
      const idx = tabRefs.current.indexOf(document.activeElement as HTMLButtonElement);
      if (idx === -1) return;
      let next: number | null = null;
      if (e.key === "ArrowRight") next = (idx + 1) % COUNT;
      else if (e.key === "ArrowLeft") next = (idx - 1 + COUNT) % COUNT;
      else if (e.key === "Home") next = 0;
      else if (e.key === "End") next = COUNT - 1;
      if (next === null) return;
      e.preventDefault();
      human();
      tabRefs.current[next]?.focus({ preventScroll: true });
      select(next);
    }

    function onTabClick(i: number) { return () => { human(); select(i); }; }
    const clickHandlers = [0, 1, 2].map(onTabClick);
    tabRefs.current.forEach((t, i) => t?.addEventListener("click", clickHandlers[i]));
    rootRef.current?.addEventListener("keydown", onKeydown);

    function loop() {
      if (!isDemo) return;
      select((active + 1) % COUNT);
      timerRef.current = window.setTimeout(loop, HOLD_MS);
    }

    if (!reduce) {
      timerRef.current = window.setTimeout(loop, HOLD_MS);
    } else {
      rootRef.current?.classList.remove(styles.isDemo);
    }

    return () => {
      window.clearTimeout(timerRef.current);
      if (rafRef.current) cancelAnimationFrame(rafRef.current);
      tabRefs.current.forEach((t, i) => t?.removeEventListener("click", clickHandlers[i]));
      rootRef.current?.removeEventListener("keydown", onKeydown);
    };
  }, []);

  const cats = [
    { name: "공지", num: "03", line: "이번 주 공지 3건" },
    { name: "리뷰", num: "128", line: "누적 리뷰 128건" },
    { name: "기록", num: "47", line: "최근 기록 47건" },
  ];

  return (
    <main className={styles.stage}>
      <div className={styles.bf + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.tabs} role="tablist" aria-label="카테고리 탭">
          {cats.map((c, i) => (
            <button
              key={c.name}
              type="button"
              className={styles.tab + (i === 0 ? " " + styles.isActive : "")}
              role="tab"
              aria-selected={i === 0 ? "true" : "false"}
              tabIndex={i === 0 ? 0 : -1}
              ref={(el: HTMLButtonElement | null) => { tabRefs.current[i] = el; }}
            >{c.name}</button>
          ))}
        </div>
        <div className={styles.wrap}>
          {cats.map((c, i) => (
            <div
              key={c.name}
              className={styles.panel + (i === 0 ? " " + styles.isFront : "")}
              role="tabpanel"
              tabIndex={0}
              hidden={i !== 0}
              ref={(el: HTMLDivElement | null) => { panelRefs.current[i] = el; }}
            >
              <span className={styles.num}>{c.num}</span>
              <p className={styles.line}>{c.line}</p>
            </div>
          ))}
        </div>
        <p className={styles.meta}>
          전환 진행률 t=<b ref={tEl}>0.00</b>
        </p>
      </div>
    </main>
  );
}