08테두리에서 채우기로

<main class="stage">
  <div class="fl-wrap is-demo">
    <span class="fl-text fl-text--outline" aria-hidden="true">SIGNATURE</span>
    <span class="fl-text fl-text--fill">SIGNATURE</span>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$easing: $ease-out;
$color: $subject-blue;

@include stage($stage-paper);

.fl-wrap {
  position: relative;
  overflow: hidden;
  font: 800 clamp(18px, 6vw, 28px)/1.2 -apple-system, "Segoe UI", sans-serif;
  letter-spacing: .02em;
}

.fl-text {
  display: block;
  white-space: nowrap;
}

.fl-text--outline {
  color: transparent;
  -webkit-text-stroke: 1px $color;
}

.fl-text--fill {
  position: absolute;
  inset: 0;
  color: $color;
  clip-path: inset(0 100% 0 0);
  filter: blur(6px);
}

// 데모 루프: 테두리만 있던 글자 위로 채워진 글자가 왼쪽부터 clip-path 로 드러났다가 다시 걷힌다
// 한 겹: blur→focus — 채움이 흘러드는 동안 blur(6px)→0 으로 잉크가 스며들 듯 초점이 맞는다
// (clip-path 는 오버슈트가 안 보이는 값이라 lerp-settle 대신 초점 수렴으로 계산 한 겹을 얹는다).
@keyframes fl-wipe {
  0%, 10% { clip-path: inset(0 100% 0 0); filter: blur(6px); }
  55%, 70% { clip-path: inset(0 0 0 0); filter: blur(0); }
  90% { clip-path: inset(0 0 0 0); filter: blur(0); }
  100% { clip-path: inset(0 100% 0 0); filter: blur(6px); }
}

.fl-wrap.is-demo .fl-text--fill { animation: fl-wipe $duration $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .fl-text--fill,
  .fl-wrap.is-demo .fl-text--fill {
    animation: none !important;
    clip-path: inset(0 0 0 0) !important;
    filter: none !important;
  }
}

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);
}

.fl-wrap {
  position: relative;
  overflow: hidden;
  font: 800 clamp(18px, 6vw, 28px)/1.2 -apple-system, "Segoe UI", sans-serif;
  letter-spacing: 0.02em;
}

.fl-text {
  display: block;
  white-space: nowrap;
}

.fl-text--outline {
  color: transparent;
  -webkit-text-stroke: 1px #2f6df6;
}

.fl-text--fill {
  position: absolute;
  inset: 0;
  color: #2f6df6;
  clip-path: inset(0 100% 0 0);
  filter: blur(6px);
}

@keyframes fl-wipe {
  0%, 10% {
    clip-path: inset(0 100% 0 0);
    filter: blur(6px);
  }
  55%, 70% {
    clip-path: inset(0 0 0 0);
    filter: blur(0);
  }
  90% {
    clip-path: inset(0 0 0 0);
    filter: blur(0);
  }
  100% {
    clip-path: inset(0 100% 0 0);
    filter: blur(6px);
  }
}
.fl-wrap.is-demo .fl-text--fill {
  animation: fl-wipe 2s ease-out infinite;
}

@media (prefers-reduced-motion: reduce) {
  .fl-text--fill,
  .fl-wrap.is-demo .fl-text--fill {
    animation: none !important;
    clip-path: inset(0 0 0 0) !important;
    filter: none !important;
  }
}

import { CSSProperties, useEffect, useRef, useState } from "react";
import styles from "./StrokeToFill.module.scss";

export interface StrokeToFillProps {
  text?: string;
  duration?: string;
  easing?: string;
}

// 실사용: 뷰포트에 들어오면 테두리만 있던 글자가 왼쪽부터 한 번 채워지며 완성된 글자로 바뀐다.
export default function StrokeToFill({
  text = "SIGNATURE",
  duration = "700ms",
  easing = "ease-out",
}: StrokeToFillProps) {
  const ref = useRef<HTMLDivElement>(null);
  const [inView, setInView] = useState(false);

  useEffect(() => {
    const el = ref.current;
    if (!el) return;
    const io = new IntersectionObserver((entries) => {
      entries.forEach((e) => { if (e.isIntersecting) { setInView(true); io.unobserve(e.target); } });
    }, { threshold: 0.3 });
    io.observe(el);
    return () => io.disconnect();
  }, []);

  const style = { "--duration": duration, "--easing": easing } as CSSProperties;

  return (
    <div className={styles.wrap} style={style} ref={ref}>
      <span className={styles.outline} aria-hidden="true">{text}</span>
      <span className={`${styles.fill} ${inView ? styles.in : ""}`}>{text}</span>
    </div>
  );
}