04対角線の長さ値だけ伸びるレトロな文字

<main class="stage">
<div class="rt is-demo" id="rt">
  <p class="rt__badge"><span class="rt__badgeLabel">影の長さ</span> <span class="rt__badgeValue" id="rtValue">4px</span></p>
  <h1 class="rt__word" id="rtWord">レトロ</h1>
</div>
</main>

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

// 핵심: 길이 값(len) 하나를 대각선 방향으로 1px 씩 반복해 그 값만큼 길게 늘어뜨린다.
// 복고 포스터에서 보던 긴 그림자 글자 — 값이 커질수록 그림자가 길어진다.

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

@include stage($stage-paper);

.rt {
  display: grid;
  gap: $sp-4;
  justify-items: center;
  text-align: center;
  padding-bottom: $sp-8;
}

.rt__badge {
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .06);
  color: $subject-ink;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.rt__word {
  margin: 0;
  font-weight: 800;
  font-size: clamp(56px, 18vw, 104px);
  line-height: 1;
  white-space: nowrap;
  color: $color;
  will-change: text-shadow;
}

@media (max-width: 340px) {
  .rt__word { font-size: clamp(40px, 20vw, 68px); }
}

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

.rt {
  display: grid;
  gap: 16px;
  justify-items: center;
  text-align: center;
  padding-bottom: 32px;
}

.rt__badge {
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.06);
  color: #17141a;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.rt__word {
  margin: 0;
  font-weight: 800;
  font-size: clamp(56px, 18vw, 104px);
  line-height: 1;
  white-space: nowrap;
  color: #17141a;
  will-change: text-shadow;
}

@media (max-width: 340px) {
  .rt__word {
    font-size: clamp(40px, 20vw, 68px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .rt__word {
    transition: none;
  }
}

(function () {
  var RETRO_MAX_LEN = 34;
  var RETRO_MIN_LEN = 4;
  var PERIOD_MS = 1000;

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

  // 값(len) 하나를 대각선 방향으로 한 칸(1px)씩 반복해 길이만큼 길게 늘어뜨린다
  function buildRetroShadow(len) {
    var parts = [];
    var n = Math.round(len);
    for (var i = 1; i <= n; i++) {
      parts.push(i + 'px ' + i + 'px 0 rgba(10,79,232,' + (0.9 - (i / n) * 0.35).toFixed(2) + ')');
    }
    return parts.join(', ');
  }

  function renderRetro(len) {
    word.style.textShadow = buildRetroShadow(len);
    value.textContent = Math.round(len) + 'px';
  }

  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;
    renderRetro(RETRO_MIN_LEN + (RETRO_MAX_LEN - RETRO_MIN_LEN) * phase);
    requestAnimationFrame(loop);
  }

  if (reduce) {
    renderRetro(RETRO_MAX_LEN);
  } else {
    requestAnimationFrame(loop);
  }
})();

// TextShadowLongDiagonalRetro — vanilla 판(run/412/demo/04-text-shadow-long-diagonal-retro/index.html) 의 React 포트.
// 길이 값(len) 하나를 대각선 방향으로 1px 씩 반복해 그 값만큼 길게 늘어뜨린다.
import { useEffect, useRef, useState } from "react";
import styles from "./TextShadowLongDiagonalRetro.module.scss";

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

const RETRO_MAX_LEN = 34;
const RETRO_MIN_LEN = 4;
const PERIOD_MS = 1000;

function buildRetroShadow(len: number): string {
  const parts: string[] = [];
  const n = Math.round(len);
  for (let i = 1; i <= n; i++) {
    parts.push(i + "px " + i + "px 0 rgba(10,79,232," + (0.9 - (i / n) * 0.35).toFixed(2) + ")");
  }
  return parts.join(", ");
}

export default function TextShadowLongDiagonalRetro() {
  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(len: number): void {
    const word = wordRef.current;
    const value = valueRef.current;
    if (!word || !value) return;
    word.style.textShadow = buildRetroShadow(len);
    value.textContent = Math.round(len) + "px";
  }

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

  useEffect(() => {
    if (reduce) {
      render(RETRO_MAX_LEN);
      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;
      render(RETRO_MIN_LEN + (RETRO_MAX_LEN - RETRO_MIN_LEN) * phase);
      frameRef.current = requestAnimationFrame(loop);
    }
    frameRef.current = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(frameRef.current);
  }, [reduce]);

  const cls = [styles.rt, demo ? styles.isDemo : ""].filter(Boolean).join(" ");
  return (
    <main className={styles.stage}>
      <div className={cls}>
        <p className={styles.badge}><span>그림자 길이</span> <span ref={valueRef}>4px</span></p>
        <h1 className={styles.word} ref={wordRef}>레트로</h1>
      </div>
    </main>
  );
}