05눈금 스냅 — 가장 가까운 눈금을 찾아 복원력으로 튕겨 붙는 단속 함수

<main class="stage">
<div class="ts" id="ts">
  <p class="ts__hint">가장 가까운 눈금을 round() 로 찾아 복원력으로 튕겨 붙입니다 — 눈금 10개</p>
  <div class="ts__wrap" id="tsWrap" role="img" aria-label="드래그가 가장 가까운 눈금에 자석처럼 튕겨 붙는 장면">
    <div class="ts__ticks" id="tsTicks"></div>
    <input class="ts__range" id="tsRange" type="range" min="0" max="100" step="1" value="50" aria-label="값 슬라이더">
  </div>
  <p class="ts__meta"><b class="ts__tag" id="tsTick">50</b><span class="ts__unit">가장 가까운 눈금 (간격 10)</span></p>
</div>
</main>

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

// 눈금 스냅(05) — 눈금 점은 장식(::before 대신 JS 로 생성한 절대배치 span), 트랙 채움과
// 썸은 pseudo-element 로 직접 커스텀한다.

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

@include stage($stage-ink);

$track-h: 8px;
$thumb-d: 20px;

.ts {
  display: flex; flex-direction: column; align-items: center; gap: $sp-3;
  width: 100%; max-width: 360px;
}

.ts__hint {
  margin: 0; font-weight: 700; font-size: clamp(10px, 2.8vw, 12px); line-height: 1.35;
  color: $subject-cream; text-align: center;
}

.ts__wrap {
  position: relative; width: 100%; height: 40px;
  display: flex; align-items: center;
  --pct: 50;
}

.ts__ticks {
  position: absolute; left: 0; right: 0; top: 50%; height: 4px; margin-top: -2px;
  pointer-events: none;
}
.ts__tick {
  position: absolute; top: 0; width: 4px; height: 4px; margin-left: -2px;
  border-radius: 50%; background: rgba($subject-cream, .40);
}

.ts__range {
  appearance: none; -webkit-appearance: none;
  width: 100%; height: $thumb-d; margin: 0; background: transparent;
  position: relative; z-index: 1;
}
.ts__range:focus-visible { outline: 2px solid $subject-cream; outline-offset: 4px; border-radius: $r-pill; }

.ts__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%));
}
.ts__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);
}
.ts__range::-moz-range-track {
  height: $track-h; border-radius: $r-pill; background: rgba($subject-cream, .16);
}
.ts__range::-moz-range-progress {
  height: $track-h; border-radius: $r-pill; background: $color;
}
.ts__range::-moz-range-thumb {
  width: $thumb-d; height: $thumb-d; border: 0; border-radius: 50%;
  background: $subject-cream; box-shadow: $shadow-press;
}

.ts__meta { margin: 0; font-size: clamp(9px, 2.4vw, 11px); color: rgba($subject-cream, .82); }
.ts__tag { font-weight: 700; color: $stage-yellow; font-variant-numeric: tabular-nums; margin-right: $sp-1; }
.ts__unit { color: rgba($subject-cream, .72); }

@media (max-width: 340px) {
  .ts { gap: $sp-2; max-width: 280px; }
  .ts__hint { font-size: 8px; }
  .ts__meta { font-size: 7px; }
}

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

.ts {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  width: 100%;
  max-width: 360px;
}

.ts__hint {
  margin: 0;
  font-weight: 700;
  font-size: clamp(10px, 2.8vw, 12px);
  line-height: 1.35;
  color: #fff7e6;
  text-align: center;
}

.ts__wrap {
  position: relative;
  width: 100%;
  height: 40px;
  display: flex;
  align-items: center;
  --pct: 50;
}

.ts__ticks {
  position: absolute;
  left: 0;
  right: 0;
  top: 50%;
  height: 4px;
  margin-top: -2px;
  pointer-events: none;
}

.ts__tick {
  position: absolute;
  top: 0;
  width: 4px;
  height: 4px;
  margin-left: -2px;
  border-radius: 50%;
  background: rgba(255, 247, 230, 0.4);
}

.ts__range {
  appearance: none;
  -webkit-appearance: none;
  width: 100%;
  height: 20px;
  margin: 0;
  background: transparent;
  position: relative;
  z-index: 1;
}

.ts__range:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 4px;
  border-radius: 999px;
}

.ts__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%));
}

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

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

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

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

.ts__meta {
  margin: 0;
  font-size: clamp(9px, 2.4vw, 11px);
  color: rgba(255, 247, 230, 0.82);
}

.ts__tag {
  font-weight: 700;
  color: #ffd23f;
  font-variant-numeric: tabular-nums;
  margin-right: 4px;
}

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

@media (max-width: 340px) {
  .ts {
    gap: 8px;
    max-width: 280px;
  }
  .ts__hint {
    font-size: 8px;
  }
  .ts__meta {
    font-size: 7px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ts__range {
    transition: none;
  }
}

// 눈금 스냅(05) — 원시 드래그 목표(rawTarget)를 매 프레임 계산하고, 그 값을 눈금
// 간격(STEP=10)으로 나눈 round() 결과를 "이산 목표(tickTarget)" 로 삼는다. pos 는
// 항상 tickTarget 을 스프링(-k(pos-tick)-c·속도)으로 뒤쫓으므로, tickTarget 이 한
// 칸 건너뛸 때마다 pos 가 살짝 지나쳤다가 튕겨 붙는다. CSS @keyframes 는 없다.
(function () {
  var root = document.getElementById('ts');
  var wrap = document.getElementById('tsWrap');
  var ticksEl = document.getElementById('tsTicks');
  var range = document.getElementById('tsRange');
  var tickEl = document.getElementById('tsTick');
  if (!root || !wrap || !ticksEl || !range || !tickEl) return;

  var MIN = 0, MAX = 100;
  var STEP = (MAX - MIN) / 10; // 변형: max/20 이면 STEP = (MAX-MIN)/20
  var K = 260, C = 22; // 스냅 스프링 상수 · 감쇠 (오버슈트 약 5%)
  var TAU = 0.16;

  for (var i = 0; i <= 10; i++) {
    var d = document.createElement('span');
    d.className = 'ts__tick';
    d.style.left = (i * 10) + '%';
    ticksEl.appendChild(d);
  }

  var rawTarget = 50;
  var pos = 50, vel = 0;

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

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var playing = true;
  function stop() { playing = false; }
  range.addEventListener('pointerdown', stop);
  range.addEventListener('keydown', stop);
  range.addEventListener('input', function () {
    rawTarget = Number(range.value);
    pos = Math.round(rawTarget / STEP) * STEP;
    vel = 0;
    range.value = String(Math.round(pos));
  });

  var segTargets = [50, 8, 77, 24, 96, 50];
  var seg = 0, segFrom = rawTarget;
  var SEG_MS = 380;
  var segStart = performance.now();
  var last = segStart;

  if (reduce) {
    rawTarget = segTargets[0];
    pos = Math.round(rawTarget / STEP) * STEP;
    range.value = String(pos);
    paint();
  } 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) % segTargets.length;
          segStart = now; elapsed = 0; segFrom = rawTarget;
        }
        var target = segTargets[seg];
        var t = elapsed / 1000;
        var k = 1 - Math.exp(-t / TAU);
        rawTarget = segFrom + (target - segFrom) * k;
      }
      var tickTarget = Math.round(rawTarget / STEP) * STEP;
      var acc = -K * (pos - tickTarget) - C * vel;
      vel += acc * dt;
      pos += vel * dt;
      range.value = String(Math.round(pos));
      paint();
      requestAnimationFrame(step);
    })(last);
  }
})();

// RangeSliderTickSnapBounce — vanilla 판(run/334/demo/05-range-slider-tick-snap-bounce/index.html)
// 의 React 포트. 원시 드래그 목표(rawTarget)를 매 프레임 계산하고, 그 값을 눈금 간격(STEP=10)
// 으로 나눈 round() 결과를 "이산 목표(tickTarget)" 로 삼는다. pos 는 항상 tickTarget 을
// 스프링(-k(pos-tick)-c·속도)으로 뒤쫓으므로, tickTarget 이 한 칸 건너뛸 때마다 pos 가
// 살짝 지나쳤다가 튕겨 붙는다. CSS @keyframes 는 없다.
import { useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./RangeSliderTickSnapBounce.module.scss";

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

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

const HINT = "가장 가까운 눈금을 round() 로 찾아 복원력으로 튕겨 붙입니다 — 눈금 10개";
const ARIA_SCENE = "드래그가 가장 가까운 눈금에 자석처럼 튕겨 붙는 장면";
const RANGE_LABEL = "값 슬라이더";
const UNIT = "가장 가까운 눈금 (간격 10)";

const MIN = 0, MAX = 100;
const STEP = (MAX - MIN) / 10; // 변형: max/20 이면 STEP = (MAX-MIN)/20
const K = 260, C = 22; // 스냅 스프링 상수 · 감쇠 (오버슈트 약 5%)
const TAU = 0.16;
const SEG_TARGETS = [50, 8, 77, 24, 96, 50];
const SEG_MS = 380;

export default function RangeSliderTickSnapBounce({
  duration = "220ms",
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#2f6df6"
}: RangeSliderTickSnapBounceProps) {
  const wrapRef = useRef<HTMLDivElement | null>(null);
  const ticksRef = useRef<HTMLDivElement | null>(null);
  const rangeRef = useRef<HTMLInputElement | null>(null);
  const tickRef = useRef<HTMLElement | null>(null);
  const rafRef = useRef(0) as Box<number>;

  useEffect(() => {
    const wrap = wrapRef.current;
    const ticksEl = ticksRef.current;
    const range = rangeRef.current;
    const tickEl = tickRef.current;
    if (!wrap || !ticksEl || !range || !tickEl) return;

    for (let i = 0; i <= 10; i++) {
      const d = document.createElement("span");
      d.className = styles.tick;
      d.style.left = i * 10 + "%";
      ticksEl.appendChild(d);
    }

    let rawTarget = 50;
    let pos = 50, vel = 0;

    function paint(): void {
      const pct = ((pos - MIN) / (MAX - MIN)) * 100;
      wrap!.style.setProperty("--pct", pct.toFixed(2));
      const tick = Math.round(rawTarget / STEP) * STEP;
      tickEl!.textContent = String(Math.round(tick));
      range!.setAttribute("aria-valuenow", String(Math.round(pos)));
    }
    paint();

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    let playing = true;
    function stop(): void { playing = false; }
    const onInput = (): void => {
      rawTarget = Number(range!.value);
      pos = Math.round(rawTarget / STEP) * STEP;
      vel = 0;
      range!.value = String(Math.round(pos));
    };
    range.addEventListener("pointerdown", stop);
    range.addEventListener("keydown", stop);
    range.addEventListener("input", onInput);

    let seg = 0, segFrom = rawTarget;
    let segStart = performance.now();
    let last = segStart;

    if (reduce) {
      rawTarget = SEG_TARGETS[0];
      pos = Math.round(rawTarget / STEP) * STEP;
      range.value = String(pos);
      paint();
    } 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) % SEG_TARGETS.length;
            segStart = now; elapsed = 0; segFrom = rawTarget;
          }
          const target = SEG_TARGETS[seg];
          const t = elapsed / 1000;
          const k = 1 - Math.exp(-t / TAU);
          rawTarget = segFrom + (target - segFrom) * k;
        }
        const tickTarget = Math.round(rawTarget / STEP) * STEP;
        const acc = -K * (pos - tickTarget) - C * vel;
        vel += acc * dt;
        pos += vel * dt;
        range!.value = String(Math.round(pos));
        paint();
        rafRef.current = requestAnimationFrame(step);
      };
      rafRef.current = requestAnimationFrame(step);
    }

    return () => {
      cancelAnimationFrame(rafRef.current);
      range.removeEventListener("pointerdown", stop);
      range.removeEventListener("keydown", stop);
      range.removeEventListener("input", onInput);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <div
        className={styles.ts}
        style={{ "--duration": duration, "--easing": easing, "--color": color } as Vars}
      >
        <p className={styles.hint}>{HINT}</p>
        <div className={styles.wrap} ref={wrapRef} role="img" aria-label={ARIA_SCENE}>
          <div className={styles.ticks} ref={ticksRef}></div>
          <input
            className={styles.range}
            ref={rangeRef}
            type="range"
            min={0}
            max={100}
            step={1}
            defaultValue={50}
            aria-label={RANGE_LABEL}
          />
        </div>
        <p className={styles.meta}>
          <b className={styles.tag} ref={tickRef}>50</b>
          <span className={styles.unit}>{UNIT}</span>
        </p>
      </div>
    </main>
  );
}