01チェック線描画切替 — チェック値がオンになるとチェックマークの線の長さの値が0から最後まで順に描かれる方式

<main class="stage">
<label class="cbd is-demo" id="cbd">
  <input type="checkbox" class="cbd__input" id="cbdInput">
  <span class="cbd__box" id="cbdBox" aria-hidden="true">
    <svg class="cbd__svg" viewBox="0 0 20 20" width="14" height="14">
      <path id="cbdCheck" class="cbd__path" d="M4 10.5l3.5 3.5L16 5.5" fill="none" stroke="currentColor" stroke-width="2.6" stroke-linecap="round" stroke-linejoin="round"/>
    </svg>
  </span>
  <span class="cbd__text">利用規約に同意します</span>
</label>
</main>

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

// 계산 겹: index.html 이 SVG path.getTotalLength() 로 체크 표시의 실제 선 길이를 측정해
// stroke-dasharray 를 만들고, easeOutCubic 을 rAF 로 직접 적분해 stroke-dashoffset 을
// 0(그려짐)과 길이값(안 그려짐) 사이로 보간한다 — CSS transition 이 아니라 계산이 선을 그린다.
@include stage($stage-ink);

.cbd {
  display: flex;
  align-items: center;
  gap: $sp-3;
  cursor: pointer;
  user-select: none;
}

.cbd__input {
  position: absolute;
  width: 1px;
  height: 1px;
  opacity: 0;
  pointer-events: none;
}

.cbd__box {
  flex: 0 0 auto;
  width: 26px;
  height: 26px;
  border-radius: $r-sm;
  background: transparent;
  border: 2px solid rgba($subject-cream, .5);
  color: transparent;
  display: grid;
  place-items: center;
  box-sizing: border-box;
  transition: background-color $dur-quick $ease-out, border-color $dur-quick $ease-out, color $dur-quick $ease-out;
}

.cbd__box--on {
  background: $subject-blue;
  border-color: $subject-blue;
  color: $subject-cream;
}

.cbd__input:focus-visible + .cbd__box {
  outline: 2px solid $subject-blue-light;
  outline-offset: 2px;
}

.cbd__text {
  color: $subject-cream;
  font-size: 14px;
  font-weight: 600;
}

@media (max-width: 340px) {
  .cbd__text { font-size: 13px; }
}

@media (prefers-reduced-motion: reduce) {
  .cbd__box { transition: 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);
}

.cbd {
  display: flex;
  align-items: center;
  gap: 12px;
  cursor: pointer;
  user-select: none;
}

.cbd__input {
  position: absolute;
  width: 1px;
  height: 1px;
  opacity: 0;
  pointer-events: none;
}

.cbd__box {
  flex: 0 0 auto;
  width: 26px;
  height: 26px;
  border-radius: 8px;
  background: transparent;
  border: 2px solid rgba(255, 247, 230, 0.5);
  color: transparent;
  display: grid;
  place-items: center;
  box-sizing: border-box;
  transition: background-color 220ms ease-out, border-color 220ms ease-out, color 220ms ease-out;
}

.cbd__box--on {
  background: #2f6df6;
  border-color: #2f6df6;
  color: #fff7e6;
}

.cbd__input:focus-visible + .cbd__box {
  outline: 2px solid #5b8cf8;
  outline-offset: 2px;
}

.cbd__text {
  color: #fff7e6;
  font-size: 14px;
  font-weight: 600;
}

@media (max-width: 340px) {
  .cbd__text {
    font-size: 13px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .cbd__box {
    transition: none;
  }
}

(function () {
  var DRAW_MS = 460; // 계산 겹 상수: 체크 선이 0에서 끝까지 그려지는 데 걸리는 실제 시간(ms)
  var CYCLE_MS = 640; // 자동 루프가 체크·해제를 오가는 간격
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var root = document.getElementById('cbd');
  var input = document.getElementById('cbdInput');
  var box = document.getElementById('cbdBox');
  var path = document.getElementById('cbdCheck');

  // 계산 겹: SVG path 의 실제 길이를 getTotalLength() 로 측정해 stroke-dasharray 를 만든다 — 짐작 px 를 쓰지 않는다
  var LEN = path.getTotalLength();
  path.style.strokeDasharray = String(LEN);

  var isDemo = true;
  var drawing = false, drawStart = 0, drawFrom = LEN, drawTo = LEN;
  path.style.setProperty('stroke-dashoffset', String(LEN));

  function easeOutCubic(t) { return 1 - Math.pow(1 - t, 3); }

  function currentOffset(ts) {
    if (!drawing) return drawTo;
    var t = Math.min(1, (ts - drawStart) / DRAW_MS);
    return drawFrom + (drawTo - drawFrom) * easeOutCubic(t);
  }

  function setChecked(next, ts) {
    input.checked = next;
    box.classList.toggle('cbd__box--on', next);
    drawFrom = currentOffset(ts);
    drawTo = next ? 0 : LEN;
    drawStart = ts;
    drawing = true;
  }

  function human() {
    if (isDemo) { root.classList.remove('is-demo'); isDemo = false; }
  }

  input.addEventListener('change', function () {
    human();
    setChecked(input.checked, performance.now());
  });

  var cycleStart = 0;
  var lastState = false;

  function loop(ts) {
    if (!cycleStart) cycleStart = ts;

    if (isDemo) {
      var step = Math.floor((ts - cycleStart) / CYCLE_MS) % 2 === 1;
      if (step !== lastState) { lastState = step; setChecked(step, ts); }
    }

    if (drawing) {
      var off = currentOffset(ts);
      path.style.setProperty('stroke-dashoffset', off.toFixed(2));
      if (Math.abs(off - drawTo) < 0.05) { path.style.setProperty('stroke-dashoffset', String(drawTo)); drawing = false; }
    }

    requestAnimationFrame(loop);
  }

  if (reduce) {
    // 계산 자체는 유지하되 중간 프레임 없이 목표 값으로 바로 놓는다
    DRAW_MS = 1;
  }
  requestAnimationFrame(loop);
})();

// CheckDraw — vanilla 판(run/368/demo/01-custom-checkbox-check-draw/index.html) 의 React 포트.
// path.getTotalLength() 로 실측한 체크 선 길이를 easeOutCubic 로 rAF 적분해 strokeDashoffset 을
// 그린다 — CSS transition 이 아니라 계산으로 선을 그린다.
import { useEffect, useRef } from "react";
import styles from "./CheckDraw.module.scss";

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

export default function CheckDraw() {
  const rootRef = useRef(null) as unknown as Box<HTMLLabelElement>;
  const inputRef = useRef(null) as unknown as Box<HTMLInputElement>;
  const boxRef = useRef(null) as unknown as Box<HTMLSpanElement>;
  const pathRef = useRef(null) as unknown as Box<SVGPathElement>;
  const rafRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    let DRAW_MS = 460; // 계산 겹 상수: 체크 선이 0에서 끝까지 그려지는 데 걸리는 실제 시간(ms)
    const CYCLE_MS = 640; // 자동 루프가 체크·해제를 오가는 간격
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    const input = inputRef.current;
    const path = pathRef.current;
    if (!input || !path) return;

    let isDemo = true;
    const LEN = path.getTotalLength();
    path.style.strokeDasharray = String(LEN);
    path.style.setProperty("stroke-dashoffset", String(LEN));

    let drawing = false, drawStart = 0, drawFrom = LEN, drawTo = LEN;

    function easeOutCubic(t: number) { return 1 - Math.pow(1 - t, 3); }

    function currentOffset(ts: number) {
      if (!drawing) return drawTo;
      const t = Math.min(1, (ts - drawStart) / DRAW_MS);
      return drawFrom + (drawTo - drawFrom) * easeOutCubic(t);
    }

    function human() {
      if (isDemo) { rootRef.current?.classList.remove(styles.isDemo); isDemo = false; }
    }

    function setChecked(next: boolean, ts: number) {
      input!.checked = next;
      boxRef.current?.classList.toggle(styles.boxOn, next);
      drawFrom = currentOffset(ts);
      drawTo = next ? 0 : LEN;
      drawStart = ts;
      drawing = true;
    }

    function onChange() { human(); setChecked(input!.checked, performance.now()); }
    input.addEventListener("change", onChange);

    let cycleStart = 0;
    let lastState = false;

    function loop(ts: number) {
      if (!cycleStart) cycleStart = ts;

      if (isDemo) {
        const step = Math.floor((ts - cycleStart) / CYCLE_MS) % 2 === 1;
        if (step !== lastState) { lastState = step; setChecked(step, ts); }
      }

      if (drawing) {
        const off = currentOffset(ts);
        path!.style.setProperty("stroke-dashoffset", String(off));
        if (Math.abs(off - drawTo) < 0.05) drawing = false;
      }

      rafRef.current = requestAnimationFrame(loop);
    }

    if (reduce) { DRAW_MS = 1; }
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      input.removeEventListener("change", onChange);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <label className={styles.cbd + " " + styles.isDemo} ref={rootRef}>
        <input type="checkbox" className={styles.cbdInput} ref={inputRef} />
        <span className={styles.cbdBox} ref={boxRef} aria-hidden="true">
          <svg className={styles.cbdSvg} viewBox="0 0 20 20" width={14} height={14}>
            <path ref={pathRef} className={styles.cbdPath} d="M4 10.5l3.5 3.5L16 5.5" fill="none" stroke="currentColor" strokeWidth={2.6} strokeLinecap="round" strokeLinejoin="round" />
          </svg>
        </span>
        <span className={styles.cbdText}>약관에 동의합니다</span>
      </label>
    </main>
  );
}