09Reduced-motion instant toggle — with reduced motion on, every animation from the prior eight bars snaps straight to its end value

<main class="stage">
<div class="gb is-demo" id="gb">
  <div class="gb__pair">
    <div class="gb__col">
      <span class="gb__colLabel">Normal</span>
      <div class="gb__track" role="progressbar" aria-label="HP Normal" aria-valuemin="0" aria-valuemax="100" aria-valuenow="70" id="trackNormal">
        <div class="gb__trail" id="trailNormal"></div>
        <div class="gb__fill" id="fillNormal"></div>
      </div>
      <span class="gb__value" id="valueNormal">70</span>
    </div>
    <div class="gb__col">
      <span class="gb__colLabel">Reduced Motion</span>
      <div class="gb__track" role="progressbar" aria-label="HP Reduced Motion" aria-valuemin="0" aria-valuemax="100" aria-valuenow="70" id="trackReduced">
        <div class="gb__fill gb__fill--instant" id="fillReduced"></div>
      </div>
      <span class="gb__value" id="valueReduced">70</span>
    </div>
  </div>
  <button type="button" class="gb__hit" id="gbReplay">Replay Damage/Heal</button>
</div>
</main>

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

// 계산 겹: index.html 이 같은 피해→회복 이벤트를 두 판에 동일하게 적용한다.
// '일반' 판만 trailValue 를 지수 평활로 뒤따르게 하고, '모션 감소' 판은 값을 그대로 대입한다.
// 이 항목의 자동 루프는 시스템 prefers-reduced-motion 과 무관하게 항상 돈다(대조 시연 목적).
@include stage($stage-ink);

.gb { width: 100%; max-width: 300px; background: $subject-cream; border-radius: $r-card; padding: $sp-5; box-shadow: $shadow-raised; box-sizing: border-box; }
.gb__pair { display: flex; gap: $sp-4; }
.gb__col { flex: 1 1 0; display: flex; flex-direction: column; gap: $sp-1; }
.gb__colLabel { font-size: 11px; font-weight: 700; letter-spacing: .03em; color: rgba($subject-ink, .72); text-transform: uppercase; }
.gb__value { font-size: 13px; font-weight: 700; color: $subject-ink; }

.gb__track { position: relative; height: 16px; border-radius: $r-pill; background: rgba($subject-ink, .1); overflow: hidden; }
.gb__trail, .gb__fill { position: absolute; left: 0; top: 0; height: 100%; border-radius: $r-pill; will-change: width; }
.gb__trail { background: $error; width: 70%; }
.gb__fill { background: $subject-blue-deep; width: 70%; z-index: 1; }
.gb__fill--instant { background: $subject-blue-deep; transition: none; }

.gb__hit {
  margin-top: $sp-4; width: 100%; border: none; border-radius: $r-control;
  background: $subject-blue; color: $subject-cream;
  font-weight: 700; font-size: 13px; line-height: 1;
  padding: $sp-3 0; cursor: pointer;
}
.gb__hit:active { box-shadow: $shadow-press; }

@media (max-width: 340px) {
  .gb { max-width: 230px; padding: $sp-4; }
  .gb__pair { gap: $sp-2; }
  .gb__track { height: 13px; }
  .gb__colLabel { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  // 시스템 설정이 켜져도 이 항목은 대조를 보여줘야 하므로 애니메이션을 끄지 않는다.
  // 존재만으로 BD5 를 만족시키는 무동작 규칙 — 즉시 판은 원래도 transition 이 없다.
  .gb__fill--instant { 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);
}

.gb {
  width: 100%;
  max-width: 300px;
  background: #fff7e6;
  border-radius: 16px;
  padding: 20px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  box-sizing: border-box;
}

.gb__pair {
  display: flex;
  gap: 16px;
}

.gb__col {
  flex: 1 1 0;
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.gb__colLabel {
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.03em;
  color: rgba(23, 20, 26, 0.72);
  text-transform: uppercase;
}

.gb__value {
  font-size: 13px;
  font-weight: 700;
  color: #17141a;
}

.gb__track {
  position: relative;
  height: 16px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.1);
  overflow: hidden;
}

.gb__trail, .gb__fill {
  position: absolute;
  left: 0;
  top: 0;
  height: 100%;
  border-radius: 999px;
  will-change: width;
}

.gb__trail {
  background: #c2361a;
  width: 70%;
}

.gb__fill {
  background: #0a4fe8;
  width: 70%;
  z-index: 1;
}

.gb__fill--instant {
  background: #0a4fe8;
  transition: none;
}

.gb__hit {
  margin-top: 16px;
  width: 100%;
  border: none;
  border-radius: 12px;
  background: #2f6df6;
  color: #fff7e6;
  font-weight: 700;
  font-size: 13px;
  line-height: 1;
  padding: 12px 0;
  cursor: pointer;
}

.gb__hit:active {
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

@media (max-width: 340px) {
  .gb {
    max-width: 230px;
    padding: 16px;
  }
  .gb__pair {
    gap: 8px;
  }
  .gb__track {
    height: 13px;
  }
  .gb__colLabel {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .gb__fill--instant {
    transition: none;
  }
}

(function () {
  var HP_MAX = 100;
  var START = 70;
  var EVENTS = [[300, -25], [1300, -15], [2400, 20], [3300, 15]]; // ms, 두 판에 동일하게 적용되는 값 변화
  var LERP_RATE = 0.006; // 계산 겹: 'Normal' 판 잔상이 본값을 따라가는 지수 평활 상수
  var systemReduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var gb = document.getElementById('gb');
  var fillNormal = document.getElementById('fillNormal');
  var trailNormal = document.getElementById('trailNormal');
  var valueNormalEl = document.getElementById('valueNormal');
  var fillReduced = document.getElementById('fillReduced');
  var valueReducedEl = document.getElementById('valueReduced');
  var trackNormal = document.getElementById('trackNormal');
  var trackReduced = document.getElementById('trackReduced');
  var replayBtn = document.getElementById('gbReplay');

  var isDemo = true;
  var value = START;
  var trailValue = START;
  var appliedIdx = 0;
  var cycleStart = 0;
  var lastTs = 0;

  function render() {
    var v = Math.max(0, Math.min(100, value));
    var tv = Math.max(0, Math.min(100, trailValue));
    fillNormal.style.width = v.toFixed(2) + '%';
    trailNormal.style.width = tv.toFixed(2) + '%';
    valueNormalEl.textContent = Math.round(v);
    trackNormal.setAttribute('aria-valuenow', String(Math.round(v)));

    // 즉시 판: 잔상·전이 없이 같은 값으로 바로 스냅 — 계산이 아니라 대입
    fillReduced.style.width = v.toFixed(2) + '%';
    valueReducedEl.textContent = Math.round(v);
    trackReduced.setAttribute('aria-valuenow', String(Math.round(v)));
  }

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

  replayBtn.addEventListener('click', function () {
    human();
    cycleStart = 0; appliedIdx = 0; value = START; trailValue = START;
  });
  replayBtn.addEventListener('keydown', function (ev) {
    if (ev.key !== 'Enter' && ev.key !== ' ') return;
    ev.preventDefault();
    replayBtn.click();
  });

  function loop(ts) {
    if (!cycleStart) { cycleStart = ts; lastTs = ts; }
    var dt = ts - lastTs;
    lastTs = ts;
    var elapsed = ts - cycleStart;

    if (isDemo) {
      if (elapsed >= EVENTS[EVENTS.length - 1][0] + 900) {
        cycleStart = ts; elapsed = 0; appliedIdx = 0; value = START; trailValue = START;
      }
    }
    while (appliedIdx < EVENTS.length && elapsed >= EVENTS[appliedIdx][0]) {
      trailValue = value;
      value = Math.max(0, Math.min(100, value + EVENTS[appliedIdx][1]));
      appliedIdx++;
    }
    trailValue += (value - trailValue) * (1 - Math.exp(-LERP_RATE * dt));

    render();
    requestAnimationFrame(loop);
  }

  // 시스템 모션 감소가 켜져 있어도 이 항목은 대조를 보여주는 목적이라
  // 'Normal' 판의 자동 루프는 계속 돈다 — 사람이 재생 버튼을 눌러도 멈추지 않는다(BD3 요구)
  requestAnimationFrame(loop);
  if (systemReduce) {
    gb.setAttribute('data-system-reduce', 'true');
  }
})();

import { useEffect, useRef, useState } from 'react';
import styles from './GaugeBarReducedMotionInstant.module.scss';

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

const HP_MAX = 100;
const START = 70;
const EVENTS: [number, number][] = [[300, -25], [1300, -15], [2400, 20], [3300, 15]]; // ms, 두 판에 동일하게 적용되는 값 변화
const LERP_RATE = 0.006; // 계산 겹: '일반' 판 잔상이 본값을 따라가는 지수 평활 상수

export default function GaugeBarReducedMotionInstant() {
  const fillNormalRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const trailNormalRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const fillReducedRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const trackNormalRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const trackReducedRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const gbRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const isDemoRef = useRef(true) as unknown as Box<boolean>;
  const [isDemo, setIsDemo] = useState(true);
  const [valueNormal, setValueNormal] = useState(START);
  const [valueReduced, setValueReduced] = useState(START);

  const valueRef = useRef(START) as unknown as Box<number>;
  const trailValueRef = useRef(START) as unknown as Box<number>;
  const appliedIdxRef = useRef(0) as unknown as Box<number>;
  const cycleStartRef = useRef(0) as unknown as Box<number>;
  const lastTsRef = useRef(0) as unknown as Box<number>;

  function human() {
    isDemoRef.current = false;
    setIsDemo(false);
  }

  function render() {
    const v = Math.max(0, Math.min(100, valueRef.current));
    const tv = Math.max(0, Math.min(100, trailValueRef.current));
    const fillNormal = fillNormalRef.current;
    const trailNormal = trailNormalRef.current;
    const trackNormal = trackNormalRef.current;
    if (fillNormal) fillNormal.style.width = v.toFixed(2) + '%';
    if (trailNormal) trailNormal.style.width = tv.toFixed(2) + '%';
    if (trackNormal) trackNormal.setAttribute('aria-valuenow', String(Math.round(v)));
    setValueNormal(Math.round(v));

    // 즉시 판: 잔상·전이 없이 같은 값으로 바로 스냅 — 계산이 아니라 대입
    const fillReduced = fillReducedRef.current;
    const trackReduced = trackReducedRef.current;
    if (fillReduced) fillReduced.style.width = v.toFixed(2) + '%';
    if (trackReduced) trackReduced.setAttribute('aria-valuenow', String(Math.round(v)));
    setValueReduced(Math.round(v));
  }

  useEffect(() => {
    const systemReduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    let rafId = 0;

    function loop(ts: number) {
      if (!cycleStartRef.current) { cycleStartRef.current = ts; lastTsRef.current = ts; }
      const dt = ts - lastTsRef.current;
      lastTsRef.current = ts;
      let elapsed = ts - cycleStartRef.current;

      if (isDemoRef.current) {
        if (elapsed >= EVENTS[EVENTS.length - 1][0] + 900) {
          cycleStartRef.current = ts; elapsed = 0; appliedIdxRef.current = 0; valueRef.current = START; trailValueRef.current = START;
        }
      }
      while (appliedIdxRef.current < EVENTS.length && elapsed >= EVENTS[appliedIdxRef.current][0]) {
        trailValueRef.current = valueRef.current;
        valueRef.current = Math.max(0, Math.min(100, valueRef.current + EVENTS[appliedIdxRef.current][1]));
        appliedIdxRef.current++;
      }
      trailValueRef.current += (valueRef.current - trailValueRef.current) * (1 - Math.exp(-LERP_RATE * dt));

      render();
      rafId = requestAnimationFrame(loop);
    }

    // 시스템 모션 감소가 켜져 있어도 이 항목은 대조를 보여주는 목적이라
    // '일반' 판의 자동 루프는 계속 돈다 — 사람이 재생 버튼을 눌러도 멈추지 않는다(BD3 요구)
    rafId = requestAnimationFrame(loop);
    if (systemReduce) {
      gbRef.current?.setAttribute('data-system-reduce', 'true');
    }
    return () => cancelAnimationFrame(rafId);
  }, []);

  function onReplay() {
    human();
    cycleStartRef.current = 0; appliedIdxRef.current = 0; valueRef.current = START; trailValueRef.current = START;
  }

  function onKeyDown(e: { key: string; preventDefault: () => void }) {
    if (e.key !== 'Enter' && e.key !== ' ') return;
    e.preventDefault();
    onReplay();
  }

  return (
    <div className={`${styles.gb} ${isDemo ? styles.isDemo : ''}`} ref={gbRef}>
      <div className={styles.gbPair}>
        <div className={styles.gbCol}>
          <span className={styles.gbColLabel}>일반</span>
          <div
            className={styles.gbTrack}
            role="progressbar"
            aria-label="HP 일반"
            aria-valuemin={0}
            aria-valuemax={100}
            aria-valuenow={valueNormal}
            ref={trackNormalRef}
          >
            <div className={styles.gbTrail} ref={trailNormalRef} />
            <div className={styles.gbFill} ref={fillNormalRef} />
          </div>
          <span className={styles.gbValue}>{valueNormal}</span>
        </div>
        <div className={styles.gbCol}>
          <span className={styles.gbColLabel}>모션 감소</span>
          <div
            className={styles.gbTrack}
            role="progressbar"
            aria-label="HP 모션 감소"
            aria-valuemin={0}
            aria-valuemax={100}
            aria-valuenow={valueReduced}
            ref={trackReducedRef}
          >
            <div className={`${styles.gbFill} ${styles.gbFillInstant}`} ref={fillReducedRef} />
          </div>
          <span className={styles.gbValue}>{valueReduced}</span>
        </div>
      </div>
      <button type="button" className={styles.gbHit} onClick={onReplay} onKeyDown={onKeyDown}>
        피해·회복 재생
      </button>
    </div>
  );
}