07Letters That Read as Stacked Paper by a Layer Value

<main class="stage">
<div class="pp is-demo" id="pp">
  <p class="pp__badge"><span class="pp__badgeLabel">Paper layers</span> <span class="pp__badgeValue" id="ppValue">1</span></p>
  <h1 class="pp__word" id="ppWord">Paper</h1>
</div>
</main>

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

// 핵심: 층 값(n) 하나로 색·거리 값이 다른 종이 층을 n 장 쌓는다. n 이 늘수록 종이를
// 여러 장 겹쳐 놓은 것처럼 보이고, 줄면 한두 장만 남은 듯 보인다.

$duration: $dur-loop;
$easing: linear;
$color: $subject-ink;

@include stage($stage-orange);

.pp {
  display: grid;
  gap: $sp-4;
  justify-items: center;
  text-align: center;
}

.pp__badge {
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .12);
  color: $subject-ink;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.pp__word {
  margin: 0;
  font-weight: 800;
  font-size: clamp(68px, 22vw, 128px);
  line-height: 1;
  white-space: nowrap;
  color: $color;
  will-change: text-shadow;
}

@media (max-width: 340px) {
  .pp__word { font-size: clamp(48px, 24vw, 84px); }
}

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

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);
}

.pp {
  display: grid;
  gap: 16px;
  justify-items: center;
  text-align: center;
}

.pp__badge {
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.12);
  color: #17141a;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.pp__word {
  margin: 0;
  font-weight: 800;
  font-size: clamp(68px, 22vw, 128px);
  line-height: 1;
  white-space: nowrap;
  color: #17141a;
  will-change: text-shadow;
}

@media (max-width: 340px) {
  .pp__word {
    font-size: clamp(48px, 24vw, 84px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .pp__word {
    transition: none;
  }
}

(function () {
  var PAPER_LAYER_COUNT = 6;
  var OFFSET_STEP_PX = 12;
  var PERIOD_MS = 1000;

  var word = document.getElementById('ppWord');
  var value = document.getElementById('ppValue');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  // 층 값(n) 하나로 색·거리 값이 다른 Paper 층을 n 장 쌓는다 — n 이 늘수록 종이가
  // 여러 장 겹친 것처럼 보인다
  function buildPaperShadow(n) {
    var parts = [];
    for (var i = 1; i <= n; i++) {
      var d = (i * OFFSET_STEP_PX).toFixed(2);
      var warm = i % 2 === 0;
      var sheet = warm ? 'rgba(255,247,230,.92)' : 'rgba(246,238,222,.92)';
      parts.push(d + 'px ' + d + 'px 0 ' + sheet);
      parts.push(d + 'px ' + (Number(d) + 1.4).toFixed(2) + 'px 2px rgba(23,20,26,' + (0.22 - i * 0.02).toFixed(2) + ')');
    }
    return parts.join(', ');
  }

  function renderPaper(n) {
    word.style.textShadow = buildPaperShadow(n);
    value.textContent = String(n);
  }

  var startTime = null;
  function loop(now) {
    if (startTime === null) startTime = now;
    var t = (now - startTime) % PERIOD_MS;
    var phase = (Math.sin((t / PERIOD_MS) * Math.PI * 2 - Math.PI / 2) + 1) / 2;
    var n = 1 + Math.round(phase * (PAPER_LAYER_COUNT - 1));
    renderPaper(n);
    requestAnimationFrame(loop);
  }

  if (reduce) {
    renderPaper(PAPER_LAYER_COUNT);
  } else {
    requestAnimationFrame(loop);
  }
})();

// TextShadowPaperStackLayer — vanilla 판(run/412/demo/07-text-shadow-paper-stack-layer/index.html) 의 React 포트.
// 층 값(n) 하나로 색·거리 값이 다른 종이 층을 n 장 쌓는다 — n 이 늘수록 종이가
// 여러 장 겹친 것처럼 보인다.
import { useEffect, useRef, useState } from "react";
import styles from "./TextShadowPaperStackLayer.module.scss";

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

const PAPER_LAYER_COUNT = 6;
const OFFSET_STEP_PX = 12;
const PERIOD_MS = 1000;

function buildPaperShadow(n: number): string {
  const parts: string[] = [];
  for (let i = 1; i <= n; i++) {
    const d = (i * OFFSET_STEP_PX).toFixed(2);
    const warm = i % 2 === 0;
    const sheet = warm ? "rgba(255,247,230,.92)" : "rgba(246,238,222,.92)";
    parts.push(d + "px " + d + "px 0 " + sheet);
    parts.push(d + "px " + (Number(d) + 1.4).toFixed(2) + "px 2px rgba(23,20,26," + (0.22 - i * 0.02).toFixed(2) + ")");
  }
  return parts.join(", ");
}

export default function TextShadowPaperStackLayer() {
  const wordRef = useRef<HTMLHeadingElement | null>(null);
  const valueRef = useRef<HTMLSpanElement | null>(null);
  const t0Ref = useRef<number>(0) as Box<number>;
  const frameRef = useRef<number>(0) as Box<number>;
  const [demo] = useState(true);
  const [reduce, setReduce] = useState(false);

  function render(n: number): void {
    const word = wordRef.current;
    const value = valueRef.current;
    if (!word || !value) return;
    word.style.textShadow = buildPaperShadow(n);
    value.textContent = String(n);
  }

  useEffect(() => {
    setReduce(window.matchMedia("(prefers-reduced-motion: reduce)").matches);
  }, []);

  useEffect(() => {
    if (reduce) {
      render(PAPER_LAYER_COUNT);
      return;
    }
    function loop(now: number): void {
      if (t0Ref.current === 0) t0Ref.current = now;
      const t = (now - t0Ref.current) % PERIOD_MS;
      const phase = (Math.sin((t / PERIOD_MS) * Math.PI * 2 - Math.PI / 2) + 1) / 2;
      const n = 1 + Math.round(phase * (PAPER_LAYER_COUNT - 1));
      render(n);
      frameRef.current = requestAnimationFrame(loop);
    }
    frameRef.current = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(frameRef.current);
  }, [reduce]);

  const cls = [styles.pp, demo ? styles.isDemo : ""].filter(Boolean).join(" ");
  return (
    <main className={styles.stage}>
      <div className={cls}>
        <p className={styles.badge}><span>종이 층</span> <span ref={valueRef}>1</span></p>
        <h1 className={styles.word} ref={wordRef}>종이</h1>
      </div>
    </main>
  );
}