07Tracking squeeze

<main class="stage">
  <h2 class="tk-word is-demo">
    <span class="tk-ch" style="--x:-40px">F</span>
    <span class="tk-ch" style="--x:-20px">O</span>
    <span class="tk-ch" style="--x:0px">C</span>
    <span class="tk-ch" style="--x:20px">U</span>
    <span class="tk-ch" style="--x:40px">S</span>
  </h2>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$easing: $ease-lerp-settle; // 관성 lerp — 벌어진 글자가 목표(자간 0)를 살짝 지나쳤다 정착한다 (2026-09-15 형태 2차 한 겹)
$color: $subject-cream;

@include stage($stage-orange);

.tk-word {
  margin: 0;
  font: 700 clamp(26px, 7vw, 40px)/1.2 -apple-system, "Segoe UI", sans-serif;
  color: $color;
}

.tk-ch {
  display: inline-block;
  opacity: 0;
  transform: translateX(var(--x, 0));
  filter: blur(var(--tk-blur, 6px));
}

// 데모 루프: 글자마다 --x 만큼 벌어진 채로 있다가 0 으로 모이며 자간이 좁아지듯 보인다
// 한 겹: 수렴 구간을 $ease-lerp-settle(관성 lerp) 로 목표를 살짝 지나쳤다 되돌아오게 하고,
// 같은 구간에서 blur(var(--tk-blur))→0 으로 초점이 맞아 좁아질수록 또렷해진다.
@keyframes tk-converge {
  0% { opacity: 0; transform: translateX(var(--x, 0)); filter: blur(var(--tk-blur, 6px)); }
  35%, 80% { opacity: 1; transform: translateX(0); filter: blur(0); }
  100% { opacity: 0; transform: translateX(var(--x, 0)); filter: blur(var(--tk-blur, 6px)); }
}

.tk-word.is-demo .tk-ch { animation: tk-converge $duration $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .tk-ch,
  .tk-word.is-demo .tk-ch {
    animation: none !important;
    opacity: 1 !important;
    transform: none !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: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.tk-word {
  margin: 0;
  font: 700 clamp(26px, 7vw, 40px)/1.2 -apple-system, "Segoe UI", sans-serif;
  color: #fff7e6;
}

.tk-ch {
  display: inline-block;
  opacity: 0;
  transform: translateX(var(--x, 0));
  filter: blur(var(--tk-blur, 6px));
}

@keyframes tk-converge {
  0% {
    opacity: 0;
    transform: translateX(var(--x, 0));
    filter: blur(var(--tk-blur, 6px));
  }
  35%, 80% {
    opacity: 1;
    transform: translateX(0);
    filter: blur(0);
  }
  100% {
    opacity: 0;
    transform: translateX(var(--x, 0));
    filter: blur(var(--tk-blur, 6px));
  }
}
.tk-word.is-demo .tk-ch {
  animation: tk-converge 2s linear(0, 0.051, 0.176, 0.341, 0.518, 0.685, 0.831, 0.947, 1.032, 1.087, 1.117, 1.126, 1.121, 1.105, 1.085, 1.062, 1.041, 1.022, 1.008, 0.997, 1) infinite;
}

@media (prefers-reduced-motion: reduce) {
  .tk-ch,
  .tk-word.is-demo .tk-ch {
    animation: none !important;
    opacity: 1 !important;
    transform: none !important;
    filter: none !important;
  }
}

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

export interface TrackingSqueezeProps {
  text?: string;
  duration?: string;
  easing?: string;
  spread?: number;
}

// 실사용: 뷰포트에 들어오면 벌어져 있던 글자들이 한 번 좁혀지며 자간이 정리된 제목으로 모인다.
export default function TrackingSqueeze({
  text = "FOCUS",
  duration = "650ms",
  easing = "ease-out",
  spread = 20,
}: TrackingSqueezeProps) {
  const ref = useRef<HTMLHeadingElement>(null);
  const [inView, setInView] = useState(false);
  const chars = text.split("");
  const mid = (chars.length - 1) / 2;

  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 (
    <h2 className={styles.word} style={style} ref={ref}>
      {chars.map((ch, i) => (
        <span
          key={i}
          className={`${styles.ch} ${inView ? styles.in : ""}`}
          style={{ "--x": `${(i - mid) * spread}px` } as CSSProperties}
        >
          {ch}
        </span>
      ))}
    </h2>
  );
}