06層ごとに明るさの値が変わり光沢が乗る金属文字

<main class="stage">
<div class="mt is-demo" id="mt">
  <p class="mt__badge"><span class="mt__badgeLabel">光沢角度</span> <span class="mt__badgeValue" id="mtValue">0deg</span></p>
  <h1 class="mt__word" id="mtWord">金属</h1>
</div>
</main>

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

// 핵심: 각도 값 하나로 SHEEN_LAYER_COUNT 층마다 밝기를 사인 곡선을 따라 다르게 겹친다.
// 각도가 돌면 밝은 띠가 층을 타고 흘러 금속 표면에 빛이 지나가는 것처럼 보인다.
// 상표명 없이 「금속 광택」이라고만 부른다.

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

@include stage($stage-yellow);

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

.mt__badge {
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .08);
  color: $subject-ink;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.mt__word {
  margin: 0;
  font-weight: 800;
  font-size: clamp(72px, 24vw, 140px);
  line-height: 1;
  white-space: nowrap;
  color: $color;
  will-change: text-shadow;
}

@media (max-width: 340px) {
  .mt__word { font-size: clamp(52px, 26vw, 92px); }
}

@media (prefers-reduced-motion: reduce) {
  .mt__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: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

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

.mt__badge {
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.08);
  color: #17141a;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.mt__word {
  margin: 0;
  font-weight: 800;
  font-size: clamp(72px, 24vw, 140px);
  line-height: 1;
  white-space: nowrap;
  color: #17141a;
  will-change: text-shadow;
}

@media (max-width: 340px) {
  .mt__word {
    font-size: clamp(52px, 26vw, 92px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .mt__word {
    transition: none;
  }
}

(function () {
  var SHEEN_LAYER_COUNT = 7;
  var PERIOD_MS = 900;

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

  // 각도 값 하나로 층마다 밝기를 사인 곡선을 따라 다르게 겹쳐, 위·아래가 서로 다르게 빛나는
  // 金属 광택을 만든다. 층 위상(phase)이 갈릴수록 밝은 띠가 층을 타고 흐른다
  function buildSheenShadow(angleDeg) {
    var rad = (angleDeg * Math.PI) / 180;
    var parts = [];
    for (var i = 1; i <= SHEEN_LAYER_COUNT; i++) {
      var phase = rad + (i / SHEEN_LAYER_COUNT) * Math.PI * 1.4;
      var bright = (Math.sin(phase) + 1) / 2;
      var l = Math.round(22 + bright * 58);
      var y = (i * 6.8).toFixed(2);
      parts.push('0px ' + y + 'px 0 hsl(220 10% ' + l + '%)');
    }
    return parts.join(', ');
  }

  function renderSheen(angleDeg) {
    word.style.textShadow = buildSheenShadow(angleDeg);
    value.textContent = Math.round(angleDeg % 360) + 'deg';
  }

  var startTime = null;
  function loop(now) {
    if (startTime === null) startTime = now;
    var t = (now - startTime) % PERIOD_MS;
    var angle = (t / PERIOD_MS) * 360;
    renderSheen(angle);
    requestAnimationFrame(loop);
  }

  if (reduce) {
    renderSheen(90);
  } else {
    requestAnimationFrame(loop);
  }
})();

// TextShadowMetalSheenLayer — vanilla 판(run/412/demo/06-text-shadow-metal-sheen-layer/index.html) 의 React 포트.
// 각도 값 하나로 SHEEN_LAYER_COUNT 층마다 밝기를 사인 곡선을 따라 다르게 겹친다.
// 각도가 돌면 밝은 띠가 층을 타고 흘러 금속 표면에 빛이 지나가는 것처럼 보인다.
import { useEffect, useRef, useState } from "react";
import styles from "./TextShadowMetalSheenLayer.module.scss";

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

const SHEEN_LAYER_COUNT = 7;
const PERIOD_MS = 900;

function buildSheenShadow(angleDeg: number): string {
  const rad = (angleDeg * Math.PI) / 180;
  const parts: string[] = [];
  for (let i = 1; i <= SHEEN_LAYER_COUNT; i++) {
    const phase = rad + (i / SHEEN_LAYER_COUNT) * Math.PI * 1.4;
    const bright = (Math.sin(phase) + 1) / 2;
    const l = Math.round(22 + bright * 58);
    const y = (i * 6.8).toFixed(2);
    parts.push("0px " + y + "px 0 hsl(220 10% " + l + "%)");
  }
  return parts.join(", ");
}

export default function TextShadowMetalSheenLayer() {
  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(angleDeg: number): void {
    const word = wordRef.current;
    const value = valueRef.current;
    if (!word || !value) return;
    word.style.textShadow = buildSheenShadow(angleDeg);
    value.textContent = Math.round(angleDeg % 360) + "deg";
  }

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

  useEffect(() => {
    if (reduce) {
      render(90);
      return;
    }
    function loop(now: number): void {
      if (t0Ref.current === 0) t0Ref.current = now;
      const t = (now - t0Ref.current) % PERIOD_MS;
      const angle = (t / PERIOD_MS) * 360;
      render(angle);
      frameRef.current = requestAnimationFrame(loop);
    }
    frameRef.current = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(frameRef.current);
  }, [reduce]);

  const cls = [styles.mt, demo ? styles.isDemo : ""].filter(Boolean).join(" ");
  return (
    <main className={styles.stage}>
      <div className={cls}>
        <p className={styles.badge}><span>광택 각도</span> <span ref={valueRef}>0deg</span></p>
        <h1 className={styles.word} ref={wordRef}>금속</h1>
      </div>
    </main>
  );
}