03Loader Whose Back Card Recomputes Depth Order to Move to the Front With Each Step

<main class="stage">
<div class="ld" id="ld">
  <p class="ld__hint">Click or press the space bar to pause or restart</p>
  <div class="ld__field" id="field" role="application" aria-label="Card-stack depth-cycle test panel" tabindex="0">
    <div class="c3__deck" id="deck">
      <div class="c3__card" id="c0">1</div>
      <div class="c3__card" id="c1">2</div>
      <div class="c3__card" id="c2">3</div>
      <div class="c3__card" id="c3">4</div>
      <div class="c3__card" id="c4">5</div>
    </div>
    <b class="ld__badge" aria-hidden="true"><span class="ld__badgeNum" id="pct">0%</span><span class="ld__badgeUnit">Progress</span></b>
  </div>
</div>
</main>

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

// 카드 스택 깊이 순환 로더 — 카드마다 깊이 값(rankPos, 0=맨 앞)을 진행률의 연속 함수로 계산해
// translateZ·translateY·scale·opacity·z-index 를 매 프레임 다시 매긴다(화가 알고리즘 계열, 이산 스냅이 아니라 연속 순환).
// 395(캔버스 rAF 물리)·393(포인터 tilt) 과 다른 축 — 깊이 순위 자체를 진행률의 모듈러 함수로 계산한다.

$duration: $dur-loop;
$easing: $ease-out;
$color: $subject-cream;

@include stage($stage-orange);

.ld { display: flex; flex-direction: column; gap: $sp-2; width: 100%; max-width: 360px; }

.ld__hint {
  margin: 0;
  font-weight: 700; font-size: clamp(10px, 2.8vw, 12px); line-height: 1.35;
  color: $subject-ink;
  text-align: center;
}

.ld__field {
  position: relative; height: 208px;
  border-radius: $r-card; overflow: hidden;
  background: darken($stage-orange, 6%);
  box-shadow: inset 0 0 0 1px rgba($subject-ink, .16);
  display: grid; place-items: center;
  cursor: pointer;
  perspective: clamp(320px, 70vw, 480px);
}
.ld__field:focus-visible { outline: 2px solid $subject-ink; outline-offset: 2px; }

.c3__deck { position: relative; width: 116px; height: 74px; transform-style: preserve-3d; }

.c3__card {
  position: absolute; inset: 0;
  display: grid; place-items: center;
  border-radius: $r-sm;
  background: $color;
  color: $subject-ink;
  font-weight: 700; font-size: 20px; line-height: 1;
  box-shadow: $shadow-raised;
  will-change: transform, opacity;
}

.ld__badge {
  position: absolute; right: $sp-2; top: $sp-2;
  display: flex; align-items: baseline; gap: $sp-1;
  padding: $sp-1 $sp-2; border-radius: $r-pill;
  background: rgba($subject-ink, .78);
  color: $subject-cream; font-weight: 700; font-size: 11px;
}
.ld__badgeNum { font-size: 13px; color: $stage-yellow; }
.ld__badgeUnit { font-weight: 700; }

@media (max-width: 340px) {
  .ld { gap: $sp-1; }
  .ld__field { height: 124px; }
  .c3__deck { width: 84px; height: 54px; }
  .ld__badge { font-size: 10px; padding: 0 $sp-1; }
  .ld__badgeNum { font-size: 11px; }
}

@media (prefers-reduced-motion: reduce) {
  .ld.is-still .ld__field { cursor: default !important; }
  .ld.is-still .ld__badge { opacity: .92 !important; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ld {
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 100%;
  max-width: 360px;
}

.ld__hint {
  margin: 0;
  font-weight: 700;
  font-size: clamp(10px, 2.8vw, 12px);
  line-height: 1.35;
  color: #17141a;
  text-align: center;
}

.ld__field {
  position: relative;
  height: 208px;
  border-radius: 16px;
  overflow: hidden;
  background: rgb(100%, 20.6603641457%, 0.1568627451%);
  box-shadow: inset 0 0 0 1px rgba(23, 20, 26, 0.16);
  display: grid;
  place-items: center;
  cursor: pointer;
  perspective: clamp(320px, 70vw, 480px);
}

.ld__field:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

.c3__deck {
  position: relative;
  width: 116px;
  height: 74px;
  transform-style: preserve-3d;
}

.c3__card {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  border-radius: 8px;
  background: #fff7e6;
  color: #17141a;
  font-weight: 700;
  font-size: 20px;
  line-height: 1;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  will-change: transform, opacity;
}

.ld__badge {
  position: absolute;
  right: 8px;
  top: 8px;
  display: flex;
  align-items: baseline;
  gap: 4px;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.78);
  color: #fff7e6;
  font-weight: 700;
  font-size: 11px;
}

.ld__badgeNum {
  font-size: 13px;
  color: #ffd23f;
}

.ld__badgeUnit {
  font-weight: 700;
}

@media (max-width: 340px) {
  .ld {
    gap: 4px;
  }
  .ld__field {
    height: 124px;
  }
  .c3__deck {
    width: 84px;
    height: 54px;
  }
  .ld__badge {
    font-size: 10px;
    padding: 0 4px;
  }
  .ld__badgeNum {
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ld.is-still .ld__field {
    cursor: default !important;
  }
  .ld.is-still .ld__badge {
    opacity: 0.92 !important;
  }
}

(function () {
'use strict';
var root = document.getElementById('ld');
var field = document.getElementById('field');
var pctEl = document.getElementById('pct');
var cards = [];
for (var ci = 0; ci < 5; ci++) cards.push(document.getElementById('c' + ci));

var CARD_COUNT = 5;
var ZGAP = 22;         // 깊이 한 칸당 뒤로 물러나는 거리(px)
var YOFF = 10;          // 깊이 한 칸당 아래로 내려가는 거리(px)
var SHRINK = 0.09;      // 깊이 한 칸당 축소 비율
var OPACITY_STEP = 0.15;

var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
var LOOP = 2;
var REDUCE_P = 0.7;
var t0 = 0, raf = 0, paused = false, lastP = 0;

// 카드 i 의 현재 깊이 순위(0=맨 앞)를 진행률의 연속 모듈러 함수로 계산 — 상태를 누적하지 않고
// 매 프레임 p 하나로부터 전체 순서를 다시 구한다(화가 알고리즘과 같은 원리).
function rankOf(i, s) {
  var r = (i - s) % CARD_COUNT;
  if (r < 0) r += CARD_COUNT;
  return r;
}

function render(p) {
  lastP = p;
  var s = p * CARD_COUNT;
  for (var i = 0; i < CARD_COUNT; i++) {
    var rank = rankOf(i, s);
    var z = -rank * ZGAP;
    var y = rank * YOFF;
    var scale = 1 - rank * SHRINK;
    var op = 1 - rank * OPACITY_STEP;
    cards[i].style.transform = 'translateY(' + y + 'px) translateZ(' + z + 'px) scale(' + scale + ')';
    cards[i].style.opacity = String(Math.max(0.25, op));
    cards[i].style.zIndex = String(Math.round((CARD_COUNT - rank) * 1000));
  }
  pctEl.textContent = Math.round(p * 100) + '%';
}

function frame(now) {
  if (!paused) { var t = (now - t0) / 1000; render((t % LOOP) / LOOP); }
  raf = requestAnimationFrame(frame);
}
function togglePause() {
  paused = !paused;
  root.classList.toggle('is-paused', paused);
  render(reduce ? REDUCE_P : lastP);
}
function restart() {
  t0 = performance.now();
  render(reduce ? REDUCE_P : 0);
}

field.addEventListener('click', function () { togglePause(); });
field.addEventListener('keydown', function (e) {
  if (e.key === ' ' || e.key === 'Enter') { e.preventDefault(); togglePause(); }
  else if (e.key === 'r' || e.key === 'R') { e.preventDefault(); restart(); }
});
window.addEventListener('resize', function () {
  if (paused || reduce) render(reduce ? REDUCE_P : lastP);
});

t0 = performance.now();
if (reduce) {
  root.classList.add('is-still');
  render(REDUCE_P);
} else {
  raf = requestAnimationFrame(frame);
}
})();

// CardStackDepthCycle — vanilla 판(run/399/demo/03-loader-3d-card-stack-depth-cycle/index.html) 의 React 포트.
// 카드 i 의 깊이 순위를 진행률의 연속 모듈러 함수로 계산해 매 프레임 transform·opacity·z-index 를 다시 매긴다.
// 395(캔버스 rAF 물리)·393(포인터 tilt) 과 다른 축 — 깊이 순위 자체를 진행률의 모듈러 함수로 계산한다.
import { useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./CardStackDepthCycle.module.scss";

export type CardStackDepthCycleProps = {
  duration?: string;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };
type KeyEvt = { key: string; preventDefault(): void };

const CARD_COUNT = 5;
const ZGAP = 22;
const YOFF = 10;
const SHRINK = 0.09;
const OPACITY_STEP = 0.15;
const LOOP = 2;
const REDUCE_P = 0.7;
const FIELD_LABEL = "카드 스택 깊이 순환 진행 실험판";

function rankOf(i: number, s: number): number {
  let r = (i - s) % CARD_COUNT;
  if (r < 0) r += CARD_COUNT;
  return r;
}

export default function CardStackDepthCycle({
  duration = "2s",
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#fff7e6",
}: CardStackDepthCycleProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const fieldRef = useRef<HTMLDivElement | null>(null);
  const pctRef = useRef<HTMLSpanElement | null>(null);
  const cardsRef = useRef<(HTMLDivElement | null)[]>([null, null, null, null, null]) as Box<(HTMLDivElement | null)[]>;
  const pausedRef = useRef(false) as Box<boolean>;
  const lastPRef = useRef(0) as Box<number>;
  const t0Ref = useRef(0) as Box<number>;
  const rafRef = useRef(0) as Box<number>;
  const vars: Vars = { "--duration": duration, "--easing": easing, "--color": color };

  function reduced(): boolean {
    return window.matchMedia("(prefers-reduced-motion: reduce)").matches;
  }

  function render(p: number): void {
    lastPRef.current = p;
    const s = p * CARD_COUNT;
    const cards = cardsRef.current;
    for (let i = 0; i < CARD_COUNT; i++) {
      const el = cards[i];
      if (!el) continue;
      const rank = rankOf(i, s);
      const z = -rank * ZGAP;
      const y = rank * YOFF;
      const scale = 1 - rank * SHRINK;
      const op = Math.max(0.25, 1 - rank * OPACITY_STEP);
      el.style.transform = "translateY(" + y + "px) translateZ(" + z + "px) scale(" + scale + ")";
      el.style.opacity = String(op);
      el.style.zIndex = String(Math.round((CARD_COUNT - rank) * 1000));
    }
    if (pctRef.current) pctRef.current.textContent = Math.round(p * 100) + "%";
  }

  function togglePause(): void {
    pausedRef.current = !pausedRef.current;
    const root = rootRef.current;
    if (root) root.classList.toggle("is-paused", pausedRef.current);
    render(reduced() ? REDUCE_P : lastPRef.current);
  }

  function restart(): void {
    t0Ref.current = performance.now();
    render(reduced() ? REDUCE_P : 0);
  }

  function onKey(e: KeyEvt): void {
    if (e.key === " " || e.key === "Enter") { e.preventDefault(); togglePause(); }
    else if (e.key === "r" || e.key === "R") { e.preventDefault(); restart(); }
  }

  function onClick(): void {
    togglePause();
  }

  function onResize(): void {
    if (pausedRef.current || reduced()) render(reduced() ? REDUCE_P : lastPRef.current);
  }

  function frame(now: number): void {
    if (!pausedRef.current) {
      const t = (now - t0Ref.current) / 1000;
      render((t % LOOP) / LOOP);
    }
    rafRef.current = requestAnimationFrame(frame);
  }

  useEffect(() => {
    t0Ref.current = performance.now();
    window.addEventListener("resize", onResize);
    if (reduced()) {
      const root = rootRef.current;
      if (root) root.classList.add("is-still");
      render(REDUCE_P);
    } else {
      rafRef.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.root} ref={rootRef} style={vars}>
        <p className={styles.hint}>클릭하거나 스페이스바를 누르면 멈추거나 다시 갑니다</p>
        <div
          className={styles.field}
          ref={fieldRef}
          role="application"
          aria-label={FIELD_LABEL}
          tabIndex={0}
          onClick={onClick}
          onKeyDown={onKey}
        >
          <div className={styles.deck}>
            {[1, 2, 3, 4, 5].map((n, i) => (
              <div key={n} className={styles.card} ref={(el: HTMLDivElement | null) => { cardsRef.current[i] = el; }}>{n}</div>
            ))}
          </div>
          <b className={styles.badge} aria-hidden="true"><span className={styles.badgeNum} ref={pctRef}>0%</span><span className={styles.badgeUnit}>진행</span></b>
        </div>
      </div>
    </main>
  );
}