04인덱스 거리 값이 눕히는 스택 패널

<main class="stage">
<div class="sd is-demo" id="sd">
  <div class="sd__tabs" role="tablist" aria-label="카테고리 탭">
    <button type="button" class="sd__tab is-active" role="tab" id="sd-tab-0" aria-selected="true" aria-controls="sd-panel-0" data-idx="0">풍경</button>
    <button type="button" class="sd__tab" role="tab" id="sd-tab-1" aria-selected="false" aria-controls="sd-panel-1" data-idx="1" tabindex="-1">인물</button>
    <button type="button" class="sd__tab" role="tab" id="sd-tab-2" aria-selected="false" aria-controls="sd-panel-2" data-idx="2" tabindex="-1">정물</button>
  </div>
  <div class="sd__wrap" id="sdWrap">
    <div class="sd__panel" id="sd-panel-0" role="tabpanel" aria-labelledby="sd-tab-0" tabindex="0" style="--d:0"><span class="sd__num">01</span><p class="sd__line">풍경 12장</p></div>
    <div class="sd__panel" id="sd-panel-1" role="tabpanel" aria-labelledby="sd-tab-1" tabindex="0" aria-hidden="true" style="--d:1"><span class="sd__num">02</span><p class="sd__line">인물 8장</p></div>
    <div class="sd__panel" id="sd-panel-2" role="tabpanel" aria-labelledby="sd-tab-2" tabindex="0" aria-hidden="true" style="--d:2"><span class="sd__num">03</span><p class="sd__line">정물 5장</p></div>
  </div>
  <p class="sd__meta">거리 <b id="sdDist">0</b>칸 · scale <b id="sdScale">1.00</b></p>
</div>
</main>

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

// 계산 겹: index.html apply() 가 |탭 인덱스 - 활성 인덱스| 로 정수 거리(--d)를 구해 각 패널에 심는다.
// 이 scss 는 그 --d 하나로 scale·translateY·translateZ·opacity·filter 를 calc() 로 유도한다 —
// 값이 바뀔 때마다 transform·opacity·filter 가 transition 대상이라 자동으로 부드럽게 물러난다.
@include stage($stage-paper);

.sd { width: min(100%, 300px); min-width: 0; display: flex; flex-direction: column; gap: $sp-3; }
.sd__tabs { display: flex; gap: $sp-1; background: rgba($subject-ink, .06); padding: $sp-1; border-radius: $r-pill; }
.sd__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-ink, .68);
}
.sd__tab.is-active { background: $subject-blue-deep; color: $subject-cream; }
.sd__tab:focus-visible { outline: 2px solid $subject-blue-deep; outline-offset: 2px; }

.sd__wrap { position: relative; min-width: 0; height: 150px; perspective: 900px; }
.sd__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;
  border-radius: $r-card; background: $subject-cream; box-shadow: 0 6px 18px rgba($subject-ink, .12);
  transform-origin: center 70%;
  transform:
    translateY(calc(var(--d) * 10px))
    translateZ(calc(var(--d) * -40px))
    scale(calc(1 - var(--d) * 0.08));
  opacity: calc(1 - var(--d) * 0.22);
  filter: brightness(calc(1 - var(--d) * 0.12));
  z-index: calc(3 - var(--d));
  transition: transform $dur-base $ease-out, opacity $dur-base $ease-out, filter $dur-base $ease-out;
}
.sd__panel[aria-hidden="true"] { pointer-events: none; }
.sd__num { font-size: 30px; font-weight: 800; color: $subject-blue-deep; }
.sd__line { margin: 0; font-size: 12px; color: rgba($subject-ink, .72); }

.sd__meta { margin: 0; font-size: 11px; color: rgba($subject-ink, .68); text-align: center; }
.sd__meta b { color: $subject-ink; font-weight: 700; }

@media (max-width: 340px) {
  .sd { width: 100%; gap: $sp-2; }
  .sd__tab { padding: $sp-1 $sp-2; }
  .sd__wrap { height: 96px; }
  .sd__num { font-size: 24px; }
}

@media (prefers-reduced-motion: reduce) {
  .sd__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: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.sd {
  width: min(100%, 300px);
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.sd__tabs {
  display: flex;
  gap: 4px;
  background: rgba(23, 20, 26, 0.06);
  padding: 4px;
  border-radius: 999px;
}

.sd__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(23, 20, 26, 0.68);
}

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

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

.sd__wrap {
  position: relative;
  min-width: 0;
  height: 150px;
  perspective: 900px;
}

.sd__panel {
  position: absolute;
  inset: 0;
  box-sizing: border-box;
  padding: 16px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border-radius: 16px;
  background: #fff7e6;
  box-shadow: 0 6px 18px rgba(23, 20, 26, 0.12);
  transform-origin: center 70%;
  transform: translateY(calc(var(--d) * 10px)) translateZ(calc(var(--d) * -40px)) scale(calc(1 - var(--d) * 0.08));
  opacity: calc(1 - var(--d) * 0.22);
  filter: brightness(calc(1 - var(--d) * 0.12));
  z-index: calc(3 - var(--d));
  transition: transform 300ms ease-out, opacity 300ms ease-out, filter 300ms ease-out;
}

.sd__panel[aria-hidden=true] {
  pointer-events: none;
}

.sd__num {
  font-size: 30px;
  font-weight: 800;
  color: #0a4fe8;
}

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

.sd__meta {
  margin: 0;
  font-size: 11px;
  color: rgba(23, 20, 26, 0.68);
  text-align: center;
}

.sd__meta b {
  color: #17141a;
  font-weight: 700;
}

@media (max-width: 340px) {
  .sd {
    width: 100%;
    gap: 8px;
  }
  .sd__tab {
    padding: 4px 8px;
  }
  .sd__wrap {
    height: 96px;
  }
  .sd__num {
    font-size: 24px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sd__panel {
    transition: none;
  }
}

(function () {
  var SCALE_STEP = 0.08; // 계산 겹 상수: 인덱스 거리 1칸마다 scale 이 이만큼 줄어든다
  var HOLD_MS = 780;
  var COUNT = 3;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var root = document.getElementById('sd');
  var distEl = document.getElementById('sdDist');
  var scaleEl = document.getElementById('sdScale');
  var tabs = [0, 1, 2].map(function (i) { return document.getElementById('sd-tab-' + i); });
  var panels = [0, 1, 2].map(function (i) { return document.getElementById('sd-panel-' + i); });

  var isDemo = true;
  var active = 0;

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

  function apply() {
    panels.forEach(function (p, i) {
      var d = Math.abs(i - active); // 계산 겹: 활성 탭과의 정수 인덱스 거리
      p.style.setProperty('--d', String(d));
      p.setAttribute('aria-hidden', d === 0 ? 'false' : 'true');
    });
    var scale = (1 - SCALE_STEP).toFixed(2); // 바로 다음 겹(거리1)의 scale 값을 대표로 표시
    distEl.textContent = '1';
    scaleEl.textContent = scale;
  }

  function select(idx) {
    if (idx === active) return;
    tabs[active].classList.remove('is-active');
    tabs[active].setAttribute('aria-selected', 'false');
    tabs[active].setAttribute('tabindex', '-1');
    tabs[idx].classList.add('is-active');
    tabs[idx].setAttribute('aria-selected', 'true');
    tabs[idx].setAttribute('tabindex', '0');
    active = idx;
    apply();
  }

  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');
  }
})();

// TabStackDepthScale — vanilla 판(run/394/demo/04-tab-panel-stack-depth-scale/index.html) 의 React 포트.
// apply() 가 |탭 인덱스 - 활성 인덱스| 로 정수 거리(--d)를 구해 각 패널에 심으면, module.scss 의
// calc(var(--d) * ...) 가 scale·translateY·translateZ·opacity·filter 를 유도해 물러난다.
import { useEffect, useRef, CSSProperties } from "react";
import styles from "./TabStackDepthScale.module.scss";

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

const SCALE_STEP = 0.08; // 계산 겹 상수: 인덱스 거리 1칸마다 scale 이 이만큼 줄어든다
const HOLD_MS = 780;
const COUNT = 3;

export default function TabStackDepthScale() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const distRef = useRef(null) as unknown as Box<HTMLElement>;
  const scaleRef = 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>;

  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 apply() {
      panelRefs.current.forEach((p, i) => {
        if (!p) return;
        const d = Math.abs(i - active); // 계산 겹: 활성 탭과의 정수 인덱스 거리
        p.style.setProperty("--d", String(d));
        p.setAttribute("aria-hidden", d === 0 ? "false" : "true");
      });
      if (distRef.current) distRef.current.textContent = "1";
      if (scaleRef.current) scaleRef.current.textContent = (1 - SCALE_STEP).toFixed(2);
    }

    function select(idx: number) {
      if (idx === active) return;
      const prevTab = tabRefs.current[active], 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");
      active = idx;
      apply();
    }

    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);
      tabRefs.current.forEach((t, i) => t?.removeEventListener("click", clickHandlers[i]));
      rootRef.current?.removeEventListener("keydown", onKeydown);
    };
  }, []);

  const cats = [
    { name: "풍경", num: "01", line: "풍경 12장" },
    { name: "인물", num: "02", line: "인물 8장" },
    { name: "정물", num: "03", line: "정물 5장" },
  ];

  return (
    <main className={styles.stage}>
      <div className={styles.sd + " " + 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}
              role="tabpanel"
              tabIndex={0}
              aria-hidden={i === 0 ? "false" : "true"}
              style={{ ["--d" as string]: String(i) } as CSSProperties}
              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}>
          거리 <b ref={distRef}>0</b>칸 · scale <b ref={scaleRef}>1.00</b>
        </p>
      </div>
    </main>
  );
}