09Reduced motion — turning inertia and springs off for instant, static values

<main class="stage">
<div class="rm" id="rm">
  <p class="rm__hint">The left panel chases with a spring, the right jumps straight to the value — if the real OS setting is detected, the left one switches to instant too</p>
  <div class="rm__row">
    <div class="rm__col">
      <span class="rm__label">Normal</span>
      <div class="rm__wrap" id="rmWrapA">
        <input class="rm__range" id="rmRangeA" type="range" min="0" max="100" step="1" value="50" aria-label="Normal slider">
      </div>
    </div>
    <div class="rm__col">
      <span class="rm__label">Reduce motion</span>
      <div class="rm__wrap" id="rmWrapB">
        <input class="rm__range" id="rmRangeB" type="range" min="0" max="100" step="1" value="50" aria-label="Reduced-motion slider">
      </div>
    </div>
  </div>
  <p class="rm__meta"><b class="rm__tag" id="rmMode">Detected: default</b><span class="rm__unit">prefers-reduced-motion</span></p>
</div>
</main>

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

// 동작 감소 대응(09) — 두 트랙을 나란히 두고 채움 계산은 동일한 커스텀
// 프로퍼티(--pct) 패턴으로 통일한다. 차이는 JS 쪽 위치 갱신 방식(스프링 vs 즉시)뿐.

$duration: $dur-quick;
$easing: $ease-out;
$color: $subject-blue;

@include stage($stage-ink);

$track-h: 8px;
$thumb-d: 18px;

.rm {
  display: flex; flex-direction: column; align-items: center; gap: $sp-3;
  width: 100%; max-width: 380px;
}

.rm__hint {
  margin: 0; font-weight: 700; font-size: clamp(9px, 2.6vw, 11px); line-height: 1.35;
  color: $subject-cream; text-align: center;
}

.rm__row { display: flex; gap: $sp-4; width: 100%; justify-content: center; }

.rm__col { display: flex; flex-direction: column; align-items: center; gap: $sp-2; width: 45%; }

.rm__label { font-weight: 700; font-size: 10px; color: rgba($subject-cream, .82); }

.rm__wrap {
  position: relative; width: 100%; height: 32px;
  display: flex; align-items: center;
  --pct: 50;
}

.rm__range {
  appearance: none; -webkit-appearance: none;
  width: 100%; height: $thumb-d; margin: 0; background: transparent;
}
.rm__range:focus-visible { outline: 2px solid $subject-blue-light; outline-offset: 4px; border-radius: $r-pill; }

.rm__range::-webkit-slider-runnable-track {
  height: $track-h; border-radius: $r-pill;
  background: linear-gradient(to right, $color calc(var(--pct) * 1%), rgba($subject-cream, .16) calc(var(--pct) * 1%));
}
.rm__range::-webkit-slider-thumb {
  appearance: none; -webkit-appearance: none;
  width: $thumb-d; height: $thumb-d; border-radius: 50%;
  background: $subject-cream; box-shadow: $shadow-press;
  margin-top: calc(($track-h - $thumb-d) / 2);
}
.rm__range::-moz-range-track {
  height: $track-h; border-radius: $r-pill; background: rgba($subject-cream, .16);
}
.rm__range::-moz-range-progress {
  height: $track-h; border-radius: $r-pill; background: $color;
}
.rm__range::-moz-range-thumb {
  width: $thumb-d; height: $thumb-d; border: 0; border-radius: 50%;
  background: $subject-cream; box-shadow: $shadow-press;
}

.rm__meta { margin: 0; font-size: clamp(9px, 2.2vw, 10px); color: rgba($subject-cream, .82); }
.rm__tag { font-weight: 700; color: $subject-blue-light; font-variant-numeric: tabular-nums; margin-right: $sp-1; }
.rm__unit { color: rgba($subject-cream, .72); }

@media (max-width: 340px) {
  .rm { gap: $sp-2; max-width: 280px; }
  .rm__row { gap: $sp-2; }
  .rm__hint { font-size: 7px; }
  .rm__meta { font-size: 7px; }
}

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

.rm {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  width: 100%;
  max-width: 380px;
}

.rm__hint {
  margin: 0;
  font-weight: 700;
  font-size: clamp(9px, 2.6vw, 11px);
  line-height: 1.35;
  color: #fff7e6;
  text-align: center;
}

.rm__row {
  display: flex;
  gap: 16px;
  width: 100%;
  justify-content: center;
}

.rm__col {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  width: 45%;
}

.rm__label {
  font-weight: 700;
  font-size: 10px;
  color: rgba(255, 247, 230, 0.82);
}

.rm__wrap {
  position: relative;
  width: 100%;
  height: 32px;
  display: flex;
  align-items: center;
  --pct: 50;
}

.rm__range {
  appearance: none;
  -webkit-appearance: none;
  width: 100%;
  height: 18px;
  margin: 0;
  background: transparent;
}

.rm__range:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 4px;
  border-radius: 999px;
}

.rm__range::-webkit-slider-runnable-track {
  height: 8px;
  border-radius: 999px;
  background: linear-gradient(to right, #2f6df6 calc(var(--pct) * 1%), rgba(255, 247, 230, 0.16) calc(var(--pct) * 1%));
}

.rm__range::-webkit-slider-thumb {
  appearance: none;
  -webkit-appearance: none;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: #fff7e6;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  margin-top: -5px;
}

.rm__range::-moz-range-track {
  height: 8px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.16);
}

.rm__range::-moz-range-progress {
  height: 8px;
  border-radius: 999px;
  background: #2f6df6;
}

.rm__range::-moz-range-thumb {
  width: 18px;
  height: 18px;
  border: 0;
  border-radius: 50%;
  background: #fff7e6;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

.rm__meta {
  margin: 0;
  font-size: clamp(9px, 2.2vw, 10px);
  color: rgba(255, 247, 230, 0.82);
}

.rm__tag {
  font-weight: 700;
  color: #5b8cf8;
  font-variant-numeric: tabular-nums;
  margin-right: 4px;
}

.rm__unit {
  color: rgba(255, 247, 230, 0.72);
}

@media (max-width: 340px) {
  .rm {
    gap: 8px;
    max-width: 280px;
  }
  .rm__row {
    gap: 8px;
  }
  .rm__hint {
    font-size: 7px;
  }
  .rm__meta {
    font-size: 7px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .rm__range {
    transition: none;
  }
}

// 동작 감소 대응(09) — 같은 목표값 배열을 두 패널이 같이 따라가되, 왼쪽(A)은
// 스프링 보간, 오른쪽(B)은 목표가 바뀌는 즉시 그 값으로 점프한다(애니메이션이
// 아니라 상태 전환). matchMedia('(prefers-reduced-motion: reduce)') 로 실제
// OS 설정을 읽어 reduce 이면 A 도 B 와 같은 즉시 점프로 전환한다 — 두 값 중
// 하나를 죽이는 게 아니라 "감쇠를 0 으로" 만드는 방식으로 구현 원리를 보여준다.
// aria-valuenow 는 두 패널 모두 화면 갱신과 같은 프레임에서 갈아준다.
(function () {
  var root = document.getElementById('rm');
  var wrapA = document.getElementById('rmWrapA');
  var wrapB = document.getElementById('rmWrapB');
  var rangeA = document.getElementById('rmRangeA');
  var rangeB = document.getElementById('rmRangeB');
  var modeEl = document.getElementById('rmMode');
  if (!root || !wrapA || !wrapB || !rangeA || !rangeB || !modeEl) return;

  var MIN = 0, MAX = 100;
  var K = 150, C = 17;
  var TAU = 0.13;

  var mq = window.matchMedia('(prefers-reduced-motion: reduce)');
  var reduce = mq.matches;
  var MODE_TEXT = { def: 'Detected: default', reduced: 'Detected: reduced motion' };
  modeEl.textContent = reduce ? MODE_TEXT.reduced : MODE_TEXT.def;

  function paint(wrap, range, v) {
    var pct = (v - MIN) / (MAX - MIN) * 100;
    wrap.style.setProperty('--pct', pct.toFixed(2));
    range.setAttribute('aria-valuenow', String(Math.round(v)));
  }

  var posA = 50, velA = 0, target = 50;
  var posB = 50;
  paint(wrapA, rangeA, posA);
  paint(wrapB, rangeB, posB);

  var playing = true;
  function stop() { playing = false; }
  [rangeA, rangeB].forEach(function (r) {
    r.addEventListener('pointerdown', stop);
    r.addEventListener('keydown', stop);
  });
  rangeA.addEventListener('input', function () {
    stop();
    target = Number(rangeA.value); posA = target; velA = 0; posB = target;
    rangeB.value = String(target);
    paint(wrapA, rangeA, posA); paint(wrapB, rangeB, posB);
  });

  var targets = [50, 12, 88, 30, 96, 50];
  var seg = 0, segFrom = target;
  var SEG_MS = 400;
  var segStart = performance.now();
  var last = segStart;

  if (reduce) {
    target = targets[0]; posA = target; posB = target;
    rangeA.value = String(target); rangeB.value = String(target);
    paint(wrapA, rangeA, posA); paint(wrapB, rangeB, posB);
  } else {
    (function step(now) {
      var dt = Math.min((now - last) / 1000, 0.05);
      last = now;
      if (playing) {
        var elapsed = now - segStart;
        if (elapsed >= SEG_MS) {
          seg = (seg + 1) % targets.length;
          segStart = now; elapsed = 0; segFrom = target;
          posB = targets[seg];
        }
        var t = elapsed / 1000;
        var k = 1 - Math.exp(-t / TAU);
        target = segFrom + (targets[seg] - segFrom) * k;
      }
      var acc = -K * (posA - target) - C * velA;
      velA += acc * dt;
      posA += velA * dt;
      rangeA.value = String(Math.round(posA));
      rangeB.value = String(Math.round(posB));
      paint(wrapA, rangeA, posA);
      paint(wrapB, rangeB, posB);
      requestAnimationFrame(step);
    })(last);
  }
})();

// RangeSliderReducedMotionStatic — vanilla 판(run/334/demo/09-range-slider-reduced-motion-static/index.html)
// 의 React 포트. 같은 목표값 배열을 두 패널이 같이 따라가되, 왼쪽(A)은 스프링 보간,
// 오른쪽(B)은 목표가 바뀌는 즉시 그 값으로 점프한다(애니메이션이 아니라 상태 전환).
// matchMedia('(prefers-reduced-motion: reduce)') 로 실제 OS 설정을 읽어 reduce 이면 A 도
// B 와 같은 즉시 점프로 전환한다 — 두 값 중 하나를 죽이는 게 아니라 "감쇠를 0 으로" 만드는
// 방식으로 구현 원리를 보여준다. aria-valuenow 는 두 패널 모두 화면 갱신과 같은 프레임에서 갈아준다.
import { useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./RangeSliderReducedMotionStatic.module.scss";

export type RangeSliderReducedMotionStaticProps = {
  duration?: string;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };

const HINT = "왼쪽은 스프링으로 뒤쫓고 오른쪽은 즉시 값으로 점프합니다 — 실제 OS 설정을 감지하면 왼쪽도 즉시 전환됩니다";
const LABEL_A = "일반";
const LABEL_B = "동작 줄이기";
const LABEL_RANGE_A = "일반 슬라이더";
const LABEL_RANGE_B = "동작을 줄인 슬라이더";
const MODE_DEF = "감지: 기본";
const MODE_REDUCED = "감지: 동작 줄이기";
const UNIT = "prefers-reduced-motion";

export default function RangeSliderReducedMotionStatic({
  duration = "220ms",
  easing = "ease-out",
  color = "#2f6df6"
}: RangeSliderReducedMotionStaticProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const wrapARef = useRef<HTMLDivElement | null>(null);
  const wrapBRef = useRef<HTMLDivElement | null>(null);
  const rangeARef = useRef<HTMLInputElement | null>(null);
  const rangeBRef = useRef<HTMLInputElement | null>(null);
  const modeRef = useRef<HTMLElement | null>(null);
  const rafRef = useRef(0) as Box<number>;

  useEffect(() => {
    const root = rootRef.current;
    const wrapA = wrapARef.current;
    const wrapB = wrapBRef.current;
    const rangeA = rangeARef.current;
    const rangeB = rangeBRef.current;
    const modeEl = modeRef.current;
    if (!root || !wrapA || !wrapB || !rangeA || !rangeB || !modeEl) return;

    const MIN = 0, MAX = 100;
    const K = 150, C = 17;
    const TAU = 0.13;

    const mq = window.matchMedia("(prefers-reduced-motion: reduce)");
    const reduce = mq.matches;
    modeEl.textContent = reduce ? MODE_REDUCED : MODE_DEF;

    function paint(wrap: HTMLDivElement, range: HTMLInputElement, v: number): void {
      const pct = ((v - MIN) / (MAX - MIN)) * 100;
      wrap.style.setProperty("--pct", pct.toFixed(2));
      range.setAttribute("aria-valuenow", String(Math.round(v)));
    }

    let posA = 50, velA = 0, target = 50;
    let posB = 50;
    paint(wrapA, rangeA, posA);
    paint(wrapB, rangeB, posB);

    let playing = true;
    const stop = (): void => {
      playing = false;
    };
    for (const r of [rangeA, rangeB]) {
      r.addEventListener("pointerdown", stop);
      r.addEventListener("keydown", stop);
    }
    const onInputA = (): void => {
      stop();
      target = Number(rangeA.value);
      posA = target;
      velA = 0;
      posB = target;
      rangeB.value = String(target);
      paint(wrapA, rangeA, posA);
      paint(wrapB, rangeB, posB);
    };
    rangeA.addEventListener("input", onInputA);

    const targets = [50, 12, 88, 30, 96, 50];
    let seg = 0, segFrom = target;
    const SEG_MS = 400;
    let segStart = performance.now();
    let last = segStart;

    if (reduce) {
      target = targets[0];
      posA = target;
      posB = target;
      rangeA.value = String(target);
      rangeB.value = String(target);
      paint(wrapA, rangeA, posA);
      paint(wrapB, rangeB, posB);
    } else {
      const step = (now: number): void => {
        const dt = Math.min((now - last) / 1000, 0.05);
        last = now;
        if (playing) {
          let elapsed = now - segStart;
          if (elapsed >= SEG_MS) {
            seg = (seg + 1) % targets.length;
            segStart = now;
            elapsed = 0;
            segFrom = target;
            posB = targets[seg];
          }
          const t = elapsed / 1000;
          const k = 1 - Math.exp(-t / TAU);
          target = segFrom + (targets[seg] - segFrom) * k;
        }
        const acc = -K * (posA - target) - C * velA;
        velA += acc * dt;
        posA += velA * dt;
        rangeA.value = String(Math.round(posA));
        rangeB.value = String(Math.round(posB));
        paint(wrapA, rangeA, posA);
        paint(wrapB, rangeB, posB);
        rafRef.current = requestAnimationFrame(step);
      };
      step(last);
    }

    return () => {
      for (const r of [rangeA, rangeB]) {
        r.removeEventListener("pointerdown", stop);
        r.removeEventListener("keydown", stop);
      }
      rangeA.removeEventListener("input", onInputA);
      cancelAnimationFrame(rafRef.current);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <div
        className={styles.rm}
        ref={rootRef}
        style={{ "--duration": duration, "--easing": easing, "--color": color } as Vars}
      >
        <p className={styles.hint}>{HINT}</p>
        <div className={styles.row}>
          <div className={styles.col}>
            <span className={styles.label}>{LABEL_A}</span>
            <div className={styles.wrap} ref={wrapARef}>
              <input
                className={styles.range}
                ref={rangeARef}
                type="range"
                min={0}
                max={100}
                step={1}
                defaultValue={50}
                aria-label={LABEL_RANGE_A}
              />
            </div>
          </div>
          <div className={styles.col}>
            <span className={styles.label}>{LABEL_B}</span>
            <div className={styles.wrap} ref={wrapBRef}>
              <input
                className={styles.range}
                ref={rangeBRef}
                type="range"
                min={0}
                max={100}
                step={1}
                defaultValue={50}
                aria-label={LABEL_RANGE_B}
              />
            </div>
          </div>
        </div>
        <p className={styles.meta}>
          <b className={styles.tag} ref={modeRef}>{MODE_DEF}</b>
          <span className={styles.unit}>{UNIT}</span>
        </p>
      </div>
    </main>
  );
}