09Carousel That Crossfades Cards Back Into Depth

<main class="stage">
<section class="carousel is-demo" id="carousel" role="region" aria-roledescription="carousel" aria-label="Card carousel">
  <div class="viewport" id="viewport" tabindex="0">
    <div class="layers" id="layers">
      <div class="card card--0"><span class="num">1</span></div>
      <div class="card card--1"><span class="num">2</span></div>
      <div class="card card--2"><span class="num">3</span></div>
      <div class="card card--3"><span class="num">4</span></div>
      <div class="card card--4"><span class="num">5</span></div>
    </div>
  </div>
  <button type="button" class="navBtn navBtn--prev" id="prevBtn" aria-label="Previous card">
    <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true"><g fill="currentColor"><path d="M112 56v144l-72-72Z" opacity=".2"/><path d="M216 120h-96V56a8 8 0 0 0-13.66-5.66l-72 72a8 8 0 0 0 0 11.32l72 72A8 8 0 0 0 120 200v-64h96a8 8 0 0 0 0-16m-112 60.69L51.31 128L104 75.31Z"/></g></svg>
  </button>
  <button type="button" class="navBtn navBtn--next" id="nextBtn" aria-label="Next card">
    <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true"><g fill="currentColor"><path d="m216 128l-72 72V56Z" opacity=".2"/><path d="m221.66 122.34l-72-72A8 8 0 0 0 136 56v64H40a8 8 0 0 0 0 16h96v64a8 8 0 0 0 13.66 5.66l72-72a8 8 0 0 0 0-11.32M152 180.69V75.31L204.69 128Z"/></g></svg>
  </button>
  <div class="dots" id="dots" role="tablist" aria-label="Jump to card"></div>
  <div class="readout" id="readout" aria-live="polite"></div>
</section>
</main>

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

// 변수 3개
$duration: $dur-base;
$easing: $ease-out;
$color: $subject-mint;

// 계산 겹: index.html 의 goTo() 가 CSS 트랜지션 없이 매 프레임 삼차 이징(easeInOutCubic)으로
// opacity·scale·translateZ 세 값을 동시에 계산해 나가는 카드는 가라앉고 들어오는 카드는 떠오른다.
@include stage($stage-ink);

.carousel {
  position: relative;
  width: 300px;
}

.viewport {
  position: relative;
  width: 300px;
  height: 168px;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $stage-ink;
  outline: none;
  perspective: 600px;
}

.layers {
  position: relative;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
}

.card {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  will-change: transform, opacity;

  .num {
    font-weight: 700;
    font-size: 56px;
    line-height: 1;
  }
}

.card--0 { background: linear-gradient(160deg, $subject-mint, #63b299); .num { color: $subject-ink; } }
.card--1 { background: linear-gradient(160deg, $subject-pink, #d97fa0); .num { color: $subject-ink; } }
.card--2 { background: linear-gradient(160deg, $subject-blue-deep, #475690); .num { color: $subject-cream; } }
.card--3 { background: linear-gradient(160deg, $subject-lilac, #bdb3da); .num { color: $subject-ink; } }
.card--4 { background: linear-gradient(160deg, $subject-sky, #9cb8ce); .num { color: $subject-ink; } }

.navBtn {
  position: absolute;
  top: 50%;
  margin-top: -18px;
  width: 36px;
  height: 36px;
  border-radius: $r-pill;
  border: none;
  display: grid;
  place-items: center;
  background: rgba($stage-ink, .6);
  color: $subject-cream;
  cursor: pointer;
  z-index: 4;

  &:focus-visible { outline: 2px solid $color; outline-offset: 2px; }
}
.navBtn--prev { left: -($sp-3); }
.navBtn--next { right: -($sp-3); }

.dots {
  position: absolute;
  left: 50%;
  bottom: $sp-3;
  transform: translateX(-50%);
  display: flex;
  gap: $sp-2;
  z-index: 4;
}
.dot {
  width: 8px;
  height: 8px;
  border-radius: $r-pill;
  border: none;
  background: rgba($subject-cream, .4);
  cursor: pointer;
  padding: 0;

  &.isActive { background: $subject-cream; }
  &:focus-visible { outline: 2px solid $color; outline-offset: 2px; }
}

.readout {
  position: absolute;
  right: $sp-3;
  top: $sp-3;
  padding: $sp-1 $sp-2;
  border-radius: $r-pill;
  background: rgba($stage-ink, .6);
  color: rgba($subject-cream, .9);
  font-size: 11px;
  font-weight: 600;
  line-height: 1;
  font-variant-numeric: tabular-nums;
  z-index: 4;
}

@media (max-width: 340px) {
  .carousel { width: 220px; }
  .viewport { width: 220px; height: 106px; }
  .card .num { font-size: 36px; }
  .navBtn { width: 28px; height: 28px; margin-top: -14px; }
  .dot { width: 6px; height: 6px; }
  .readout { font-size: 9px; }
}

@media (prefers-reduced-motion: reduce) {
  // 실사용 경로 적용 — 점·버튼·키보드는 index.html 이 그대로 이징 계산을 돌린다.
  // scss 만: 포커스 아웃라인 전환만 꺼서 잔여 트랜지션을 없앤다.
  .navBtn, .dot { 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);
}

.carousel {
  position: relative;
  width: 300px;
}

.viewport {
  position: relative;
  width: 300px;
  height: 168px;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #17141a;
  outline: none;
  perspective: 600px;
}

.layers {
  position: relative;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
}

.card {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  will-change: transform, opacity;
}
.card .num {
  font-weight: 700;
  font-size: 56px;
  line-height: 1;
}

.card--0 {
  background: linear-gradient(160deg, #4cd4a6, #63b299);
}
.card--0 .num {
  color: #17141a;
}

.card--1 {
  background: linear-gradient(160deg, #ff9ebb, #d97fa0);
}
.card--1 .num {
  color: #17141a;
}

.card--2 {
  background: linear-gradient(160deg, #0a4fe8, #475690);
}
.card--2 .num {
  color: #fff7e6;
}

.card--3 {
  background: linear-gradient(160deg, #b9a0ff, #bdb3da);
}
.card--3 .num {
  color: #17141a;
}

.card--4 {
  background: linear-gradient(160deg, #6ec8ff, #9cb8ce);
}
.card--4 .num {
  color: #17141a;
}

.navBtn {
  position: absolute;
  top: 50%;
  margin-top: -18px;
  width: 36px;
  height: 36px;
  border-radius: 999px;
  border: none;
  display: grid;
  place-items: center;
  background: rgba(23, 20, 26, 0.6);
  color: #fff7e6;
  cursor: pointer;
  z-index: 4;
}
.navBtn:focus-visible {
  outline: 2px solid #4cd4a6;
  outline-offset: 2px;
}

.navBtn--prev {
  left: -12px;
}

.navBtn--next {
  right: -12px;
}

.dots {
  position: absolute;
  left: 50%;
  bottom: 12px;
  transform: translateX(-50%);
  display: flex;
  gap: 8px;
  z-index: 4;
}

.dot {
  width: 8px;
  height: 8px;
  border-radius: 999px;
  border: none;
  background: rgba(255, 247, 230, 0.4);
  cursor: pointer;
  padding: 0;
}
.dot.isActive {
  background: #fff7e6;
}
.dot:focus-visible {
  outline: 2px solid #4cd4a6;
  outline-offset: 2px;
}

.readout {
  position: absolute;
  right: 12px;
  top: 12px;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.6);
  color: rgba(255, 247, 230, 0.9);
  font-size: 11px;
  font-weight: 600;
  line-height: 1;
  font-variant-numeric: tabular-nums;
  z-index: 4;
}

@media (max-width: 340px) {
  .carousel {
    width: 220px;
  }
  .viewport {
    width: 220px;
    height: 106px;
  }
  .card .num {
    font-size: 36px;
  }
  .navBtn {
    width: 28px;
    height: 28px;
    margin-top: -14px;
  }
  .dot {
    width: 6px;
    height: 6px;
  }
  .readout {
    font-size: 9px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .navBtn, .dot {
    transition: none;
  }
}

(function () {
  var TOTAL = 5;
  var CROSSFADE_MS = 480;
  var DEPTH_SCALE = 0.18;   // 페이드 도중 줄었다 늘어나는 scale 폭
  var DEPTH_PUSH = 70;      // 페이드 도중 밀려나는 translateZ(px) 깊이
  var DEMO_HOLD_MS = 620;

  var carousel = document.getElementById('carousel');
  var viewport = document.getElementById('viewport');
  var layers = document.getElementById('layers');
  var cards = Array.prototype.slice.call(layers.querySelectorAll('.card'));
  var dotsWrap = document.getElementById('dots');
  var readout = document.getElementById('readout');
  var prevBtn = document.getElementById('prevBtn');
  var nextBtn = document.getElementById('nextBtn');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var LABEL_PREFIX = 'Card ';
  var LABEL_SEP = ' / ';
  var GOTO_LABEL_PREFIX = 'Card ';
  var GOTO_LABEL_SUFFIX = ' — go to';

  var current = 0;
  var fadeFrame = null;
  var demoTimers = [];
  var dots = [];

  for (var i = 0; i < TOTAL; i++) {
    var d = document.createElement('button');
    d.type = 'button';
    d.className = 'dot';
    d.setAttribute('role', 'tab');
    d.setAttribute('aria-label', GOTO_LABEL_PREFIX + (i + 1) + GOTO_LABEL_SUFFIX);
    (function (idx) { d.addEventListener('click', function () { human(); goTo(idx); }); })(i);
    dotsWrap.appendChild(d);
    dots.push(d);
  }

  // 이징 겹 — CSS 트랜지션이 아니라 매 프레임 p 를 직접 삼차 이징으로 굽혀
  // opacity·scale·translateZ 세 값을 동시에 계산한다.
  function easeInOutCubic(p) {
    return p < 0.5 ? 4 * p * p * p : 1 - Math.pow(-2 * p + 2, 3) / 2;
  }

  function paintStatic() {
    cards.forEach(function (el, n) {
      var active = n === current;
      el.style.opacity = active ? '1' : '0';
      el.style.transform = active ? 'translateZ(0) scale(1)' : 'translateZ(' + (-DEPTH_PUSH) + 'px) scale(' + (1 - DEPTH_SCALE).toFixed(3) + ')';
      el.style.zIndex = active ? '2' : '1';
    });
    dots.forEach(function (el, n) { el.classList.toggle('isActive', n === current); });
    readout.textContent = LABEL_PREFIX + (current + 1) + LABEL_SEP + TOTAL;
  }

  function stopFade() {
    if (fadeFrame) { cancelAnimationFrame(fadeFrame); fadeFrame = null; }
  }

  function goTo(target) {
    target = ((target % TOTAL) + TOTAL) % TOTAL;
    if (target === current) return;
    stopFade();
    var from = current, to = target;
    var fromEl = cards[from], toEl = cards[to];
    toEl.style.zIndex = '2';
    fromEl.style.zIndex = '1';
    var start = performance.now();
    function frame(now) {
      var raw = Math.min(1, (now - start) / CROSSFADE_MS);
      var p = easeInOutCubic(raw);
      fromEl.style.opacity = (1 - p).toFixed(3);
      fromEl.style.transform = 'translateZ(' + (-p * DEPTH_PUSH).toFixed(1) + 'px) scale(' + (1 - p * DEPTH_SCALE).toFixed(3) + ')';
      toEl.style.opacity = p.toFixed(3);
      toEl.style.transform = 'translateZ(' + (-(1 - p) * DEPTH_PUSH).toFixed(1) + 'px) scale(' + (1 - DEPTH_SCALE + p * DEPTH_SCALE).toFixed(3) + ')';
      if (raw < 1) {
        fadeFrame = requestAnimationFrame(frame);
      } else {
        current = to;
        fadeFrame = null;
        dots.forEach(function (el, n) { el.classList.toggle('isActive', n === current); });
        readout.textContent = LABEL_PREFIX + (current + 1) + LABEL_SEP + TOTAL;
      }
    }
    fadeFrame = requestAnimationFrame(frame);
  }

  function human() {
    if (carousel.classList.contains('is-demo')) {
      carousel.classList.remove('is-demo');
      demoTimers.forEach(function (t) { clearTimeout(t); });
      demoTimers = [];
    }
  }

  prevBtn.addEventListener('click', function () { human(); goTo(current - 1); });
  nextBtn.addEventListener('click', function () { human(); goTo(current + 1); });
  function onKeydown(e) {
    if (e.key === 'ArrowLeft') { human(); goTo(current - 1); e.preventDefault(); }
    else if (e.key === 'ArrowRight') { human(); goTo(current + 1); e.preventDefault(); }
  }
  viewport.addEventListener('keydown', onKeydown);

  // reduce: 실사용 경로 적용 — 점·버튼·키보드는 위 리스너가 그대로 이징 계산을 돌린다.
  // 아래 demoCycle() 은 시연 게이트만이고 reduce 에서는 돌지 않는다.
  function demoCycle(i) {
    if (!carousel.classList.contains('is-demo')) return;
    goTo(current + 1);
    demoTimers.push(setTimeout(function () { demoCycle(i + 1); }, DEMO_HOLD_MS));
  }

  function init() {
    paintStatic();
    if (!reduce) demoCycle(0);
  }
  init();
})();

import { useEffect, useRef } from 'react';
import styles from './CarouselCrossfadeDepth.module.scss';

// 상수 — vanilla demo 09 (run/384/demo/09-carousel-slide-fade-crossfade-depth/index.html) 과 동일
const TOTAL = 5;
const CROSSFADE_MS = 480;
const DEPTH_SCALE = 0.18; // 페이드 도중 줄었다 늘어나는 scale 폭
const DEPTH_PUSH = 70;    // 페이드 도중 밀려나는 translateZ(px) 깊이
const DEMO_HOLD_MS = 620;
const LABEL_PREFIX = '카드 ';
const LABEL_SEP = ' / ';
const GOTO_LABEL_PREFIX = '카드 ';
const GOTO_LABEL_SUFFIX = '로 이동';

// 이징 겹 — CSS 트랜지션이 아니라 매 프레임 p 를 직접 삼차 이징으로 굽혀
// opacity·scale·translateZ 세 값을 동시에 계산한다.
function easeInOutCubic(p: number) {
  return p < 0.5 ? 4 * p * p * p : 1 - Math.pow(-2 * p + 2, 3) / 2;
}

export default function CarouselCrossfadeDepth() {
  const carouselRef = useRef<HTMLElement>(null);

  useEffect(() => {
    const carousel = carouselRef.current;
    if (!carousel) return undefined;
    const viewport = carousel.querySelector<HTMLDivElement>('.' + styles.viewport);
    const layers = carousel.querySelector<HTMLDivElement>('.' + styles.layers);
    const dotsWrap = carousel.querySelector<HTMLDivElement>('.' + styles.dots);
    const readout = carousel.querySelector<HTMLDivElement>('.' + styles.readout);
    const prevBtn = carousel.querySelector<HTMLButtonElement>('.' + styles['navBtn--prev']);
    const nextBtn = carousel.querySelector<HTMLButtonElement>('.' + styles['navBtn--next']);
    if (!viewport || !layers || !dotsWrap || !readout || !prevBtn || !nextBtn) return undefined;
    const cards = Array.prototype.slice.call(
      layers.querySelectorAll<HTMLDivElement>('.' + styles.card)
    ) as HTMLDivElement[];

    let current = 0;
    let fadeFrame = 0;
    let demoTimers: number[] = [];
    const dots: HTMLButtonElement[] = [];
    const dotClickHandlers: (() => void)[] = [];

    dotsWrap.innerHTML = '';
    for (let i = 0; i < TOTAL; i++) {
      const d = document.createElement('button');
      d.type = 'button';
      d.className = styles.dot;
      d.setAttribute('role', 'tab');
      d.setAttribute('aria-label', GOTO_LABEL_PREFIX + (i + 1) + GOTO_LABEL_SUFFIX);
      const idx = i;
      const handler = () => { human(); goTo(idx); };
      dotClickHandlers.push(handler);
      d.addEventListener('click', handler);
      dotsWrap.appendChild(d);
      dots.push(d);
    }

    function paintStatic() {
      cards.forEach((el, n) => {
        const active = n === current;
        el.style.opacity = active ? '1' : '0';
        el.style.transform = active
          ? 'translateZ(0) scale(1)'
          : 'translateZ(' + -DEPTH_PUSH + 'px) scale(' + (1 - DEPTH_SCALE).toFixed(3) + ')';
        el.style.zIndex = active ? '2' : '1';
      });
      dots.forEach((el, n) => el.classList.toggle(styles.isActive, n === current));
      readout!.textContent = LABEL_PREFIX + (current + 1) + LABEL_SEP + TOTAL;
    }

    function stopFade() {
      if (fadeFrame) { cancelAnimationFrame(fadeFrame); fadeFrame = 0; }
    }

    function goTo(target: number) {
      target = ((target % TOTAL) + TOTAL) % TOTAL;
      if (target === current) return;
      stopFade();
      const from = current, to = target;
      const fromEl = cards[from], toEl = cards[to];
      toEl.style.zIndex = '2';
      fromEl.style.zIndex = '1';
      const start = performance.now();
      function frame(now: number) {
        const raw = Math.min(1, (now - start) / CROSSFADE_MS);
        const p = easeInOutCubic(raw);
        fromEl.style.opacity = (1 - p).toFixed(3);
        fromEl.style.transform = 'translateZ(' + (-p * DEPTH_PUSH).toFixed(1) + 'px) scale(' + (1 - p * DEPTH_SCALE).toFixed(3) + ')';
        toEl.style.opacity = p.toFixed(3);
        toEl.style.transform = 'translateZ(' + (-(1 - p) * DEPTH_PUSH).toFixed(1) + 'px) scale(' + (1 - DEPTH_SCALE + p * DEPTH_SCALE).toFixed(3) + ')';
        if (raw < 1) {
          fadeFrame = requestAnimationFrame(frame);
        } else {
          current = to;
          fadeFrame = 0;
          dots.forEach((el, n) => el.classList.toggle(styles.isActive, n === current));
          readout!.textContent = LABEL_PREFIX + (current + 1) + LABEL_SEP + TOTAL;
        }
      }
      fadeFrame = requestAnimationFrame(frame);
    }

    function human() {
      if (carousel!.classList.contains(styles['is-demo'])) {
        carousel!.classList.remove(styles['is-demo']);
        demoTimers.forEach((t) => window.clearTimeout(t));
        demoTimers = [];
      }
    }

    function onPrev() { human(); goTo(current - 1); }
    function onNext() { human(); goTo(current + 1); }
    function onKeydown(e: KeyboardEvent) {
      if (e.key === 'ArrowLeft') { human(); goTo(current - 1); e.preventDefault(); }
      else if (e.key === 'ArrowRight') { human(); goTo(current + 1); e.preventDefault(); }
    }

    prevBtn.addEventListener('click', onPrev);
    nextBtn.addEventListener('click', onNext);
    viewport.addEventListener('keydown', onKeydown);

    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

    // reduce: 실사용 경로 적용 — 점·버튼·키보드는 위 리스너가 그대로 이징 계산을 돌린다.
    // 아래 demoCycle() 은 시연 게이트만이고 reduce 에서는 돌지 않는다.
    function demoCycle(i: number) {
      if (!carousel!.classList.contains(styles['is-demo'])) return;
      goTo(current + 1);
      demoTimers.push(window.setTimeout(() => demoCycle(i + 1), DEMO_HOLD_MS));
    }

    paintStatic();
    if (!reduce) demoCycle(0);

    return () => {
      prevBtn.removeEventListener('click', onPrev);
      nextBtn.removeEventListener('click', onNext);
      viewport.removeEventListener('keydown', onKeydown);
      dots.forEach((d, i) => d.removeEventListener('click', dotClickHandlers[i]));
      demoTimers.forEach((t) => window.clearTimeout(t));
      stopFade();
    };
  }, []);

  return (
    <main className={styles.stage}>
      <section
        className={styles.carousel + ' ' + styles['is-demo']}
        ref={carouselRef}
        role="region"
        aria-roledescription="carousel"
        aria-label="카드 캐러셀"
      >
        <div className={styles.viewport} tabIndex={0}>
          <div className={styles.layers}>
            <div className={styles.card + ' ' + styles['card--0']}><span className={styles.num}>1</span></div>
            <div className={styles.card + ' ' + styles['card--1']}><span className={styles.num}>2</span></div>
            <div className={styles.card + ' ' + styles['card--2']}><span className={styles.num}>3</span></div>
            <div className={styles.card + ' ' + styles['card--3']}><span className={styles.num}>4</span></div>
            <div className={styles.card + ' ' + styles['card--4']}><span className={styles.num}>5</span></div>
          </div>
        </div>
        <button type="button" className={styles.navBtn + ' ' + styles['navBtn--prev']} aria-label="이전 카드">
          <svg viewBox="0 0 256 256" width={18} height={18} aria-hidden="true"><g fill="currentColor"><path d="M112 56v144l-72-72Z" opacity=".2" /><path d="M216 120h-96V56a8 8 0 0 0-13.66-5.66l-72 72a8 8 0 0 0 0 11.32l72 72A8 8 0 0 0 120 200v-64h96a8 8 0 0 0 0-16m-112 60.69L51.31 128L104 75.31Z" /></g></svg>
        </button>
        <button type="button" className={styles.navBtn + ' ' + styles['navBtn--next']} aria-label="다음 카드">
          <svg viewBox="0 0 256 256" width={18} height={18} aria-hidden="true"><g fill="currentColor"><path d="m216 128l-72 72V56Z" opacity=".2" /><path d="m221.66 122.34l-72-72A8 8 0 0 0 136 56v64H40a8 8 0 0 0 0 16h96v64a8 8 0 0 0 13.66 5.66l72-72a8 8 0 0 0 0-11.32M152 180.69V75.31L204.69 128Z" /></g></svg>
        </button>
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}