01밑에서 마스크 등장

<main class="stage">
  <div class="mask">
    <h1 class="mask__text" data-split>당신의 이야기</h1>
  </div>
</main>

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

$duration: $dur-loop;                              // 마스크가 걷히는 한 주기
$easing: $ease-spring;                             // 처음 빠르고 끝은 부드럽게
$color: $subject-cream;                            // 글자 색

@include stage($stage-ink);

.mask {
  overflow: hidden;                                // 상자 밖은 자른다 — 이게 마스크
  max-width: min(380px, 90vw);
}

.mask__text {
  margin: 0;
  font-weight: 800; font-size: clamp(26px, 8vw, 42px); line-height: 1.2; font-family: inherit;
  color: $color;
  text-align: center;
}

.mask__text .letter {
  display: inline-block;
  animation: mask-up $duration $easing infinite, letter-blur-in $duration $easing infinite;
  animation-delay: calc(var(--i) * 30ms + var(--n) * 70ms);   // --i 시차 + --n 노이즈로 기계적 정렬을 깬다
}

@keyframes mask-up {
  0%, 4%    { transform: translateY(115%); }
  30%, 78%  { transform: translateY(0); }
  96%, 100% { transform: translateY(115%); }
}

@keyframes letter-blur-in {
  0%, 4%    { filter: blur(10px); }
  30%, 78%  { filter: blur(0); }
  96%, 100% { filter: blur(10px); }
}

@media (prefers-reduced-motion: reduce) {
  .mask__text .letter { animation: none; transform: none; filter: 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);
}

.mask {
  overflow: hidden;
  max-width: min(380px, 90vw);
}

.mask__text {
  margin: 0;
  font-weight: 800;
  font-size: clamp(26px, 8vw, 42px);
  line-height: 1.2;
  font-family: inherit;
  color: #fff7e6;
  text-align: center;
}

.mask__text .letter {
  display: inline-block;
  animation: mask-up 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite, letter-blur-in 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
  animation-delay: calc(var(--i) * 30ms + var(--n) * 70ms);
}

@keyframes mask-up {
  0%, 4% {
    transform: translateY(115%);
  }
  30%, 78% {
    transform: translateY(0);
  }
  96%, 100% {
    transform: translateY(115%);
  }
}
@keyframes letter-blur-in {
  0%, 4% {
    filter: blur(10px);
  }
  30%, 78% {
    filter: blur(0);
  }
  96%, 100% {
    filter: blur(10px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .mask__text .letter {
    animation: none;
    transform: none;
    filter: none;
  }
}

(function(){
  function splitLetters(el){
    var text = el.textContent;
    el.textContent = "";
    Array.from(text).forEach(function(ch, i){
      var span = document.createElement("span");
      span.className = "letter";
      var seed = Math.sin((i + 1) * 12.9898) * 43758.5453;
      var noise = seed - Math.floor(seed);
      span.style.setProperty("--i", i);
      span.style.setProperty("--n", noise.toFixed(3));
      span.textContent = ch === " " ? " " : ch;
      el.appendChild(span);
    });
  }
  document.querySelectorAll("[data-split]").forEach(splitLetters);
})();

import type { CSSProperties } from "react";
import styles from "./MaskRevealUp.module.scss";

type Vars = CSSProperties & { "--i"?: number; "--n"?: number };

function noise(i: number): number {
  const s = Math.sin((i + 1) * 12.9898) * 43758.5453;
  return Number((s - Math.floor(s)).toFixed(3));
}

export type MaskRevealUpProps = {
  text: string;
  /** 마스크가 걷히는 한 주기 (기본 2000ms) */
  duration?: number;
  color?: string;
};

export default function MaskRevealUp({ text, duration = 2000, color = "#fff7e6" }: MaskRevealUpProps) {
  const vars = { "--duration": `${duration}ms`, "--color": color } as CSSProperties;
  const chars = Array.from(text);
  return (
    <div className={styles.mask}>
      <h1 className={styles.text} style={vars}>
        {chars.map((ch, i) => (
          <span key={i} className={styles.letter} style={{ "--i": i, "--n": noise(i) } as Vars}>
            {ch === " " ? " " : ch}
          </span>
        ))}
      </h1>
    </div>
  );
}