02Spring overshoot — a damped oscillation that pops the thumb in on change

<main class="stage">
<div class="so" id="so">
  <p class="so__hint">Every time the value changes, a spring-damper equation makes the thumb overshoot slightly then settle</p>
  <div class="so__wrap" id="soWrap" role="img" aria-label="Spring-overshoot scene where the thumb bounces and settles every time the value changes">
    <input class="so__range" id="soRange" type="range" min="0" max="100" step="1" value="50" aria-label="Value slider">
  </div>
  <p class="so__meta"><b class="so__tag" id="soScale">1.000</b><span class="so__unit">scale = integral of -k(target-current) - c·velocity</span></p>
</div>
</main>

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

// 스프링 오버슈트(02) — 썸 스케일은 JS 스프링 적분값을 --scale 로 받아
// ::-webkit-slider-thumb 에 transform: scale() 로만 얹는다. 위치·스케일 모두 rAF 계산.

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

@include stage($stage-yellow);

$track-h: 8px;
$thumb-d: 22px;

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

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

.so__wrap {
  position: relative; width: 100%; height: 40px;
  display: flex; align-items: center;
  --pct: 50; --scale: 1;
}

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

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

.so__meta { margin: 0; font-size: clamp(9px, 2.4vw, 11px); color: rgba($subject-ink, .82); }
.so__tag { font-weight: 700; color: $subject-blue-deep; font-variant-numeric: tabular-nums; margin-right: $sp-1; }
.so__unit { color: rgba($subject-ink, .72); }

@media (max-width: 340px) {
  .so { gap: $sp-2; max-width: 280px; }
  .so__hint { font-size: 8px; }
  .so__meta { font-size: 7px; }
}

@media (prefers-reduced-motion: reduce) {
  .so__range::-webkit-slider-thumb { transform: scale(1); }
  .so__range::-moz-range-thumb { transform: scale(1); }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

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

.so__hint {
  margin: 0;
  font-weight: 700;
  font-size: clamp(10px, 2.8vw, 12px);
  line-height: 1.35;
  color: #17141a;
  text-align: center;
}

.so__wrap {
  position: relative;
  width: 100%;
  height: 40px;
  display: flex;
  align-items: center;
  --pct: 50;
  --scale: 1;
}

.so__range {
  appearance: none;
  -webkit-appearance: none;
  width: 100%;
  height: 22px;
  margin: 0;
  background: transparent;
}

.so__range:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 4px;
  border-radius: 999px;
}

.so__range::-webkit-slider-runnable-track {
  height: 8px;
  border-radius: 999px;
  background: linear-gradient(to right, #2f6df6 calc(var(--pct) * 1%), rgba(23, 20, 26, 0.16) calc(var(--pct) * 1%));
}

.so__range::-webkit-slider-thumb {
  appearance: none;
  -webkit-appearance: none;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: #17141a;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  margin-top: -7px;
  transform: scale(var(--scale, 1));
  transform-origin: center center;
}

.so__range::-moz-range-track {
  height: 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.16);
}

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

.so__range::-moz-range-thumb {
  width: 22px;
  height: 22px;
  border: 0;
  border-radius: 50%;
  background: #17141a;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  transform: scale(var(--scale, 1));
  transform-origin: center center;
}

.so__meta {
  margin: 0;
  font-size: clamp(9px, 2.4vw, 11px);
  color: rgba(23, 20, 26, 0.82);
}

.so__tag {
  font-weight: 700;
  color: #0a4fe8;
  font-variant-numeric: tabular-nums;
  margin-right: 4px;
}

.so__unit {
  color: rgba(23, 20, 26, 0.72);
}

@media (max-width: 340px) {
  .so {
    gap: 8px;
    max-width: 280px;
  }
  .so__hint {
    font-size: 8px;
  }
  .so__meta {
    font-size: 7px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .so__range::-webkit-slider-thumb {
    transform: scale(1);
  }
  .so__range::-moz-range-thumb {
    transform: scale(1);
  }
}

// 스프링 오버슈트(02) — 값이 바뀌는 순간 썸 스케일에 속도 킥을 넣고, 매 프레임
// accel = -k*(scale-1) - c*velocity 를 적분해 감쇠 진동을 만든다. k·c 두 계수만으로
// 튕김의 세기와 빠르기가 정해진다. CSS @keyframes·transition 은 없다 — 위치와 스케일
// 둘 다 requestAnimationFrame 이 매 프레임 다시 계산해 그린다.
(function () {
  var root = document.getElementById('so');
  var wrap = document.getElementById('soWrap');
  var range = document.getElementById('soRange');
  var scaleEl = document.getElementById('soScale');
  if (!root || !wrap || !range || !scaleEl) return;

  var MIN = 0, MAX = 100;
  var K = 170, C = 14; // 스프링 상수 · 감쇠 계수 (임계감쇠비 약 0.54 — 12~14% 오버슈트)
  var KICK = 9; // 값이 바뀔 때 스케일 속도에 주는 충격량

  var pos = 50;      // 트랙 위 표시 값(0~100)
  var scale = 1;
  var vel = 0;

  function paint() {
    var pct = (pos - MIN) / (MAX - MIN) * 100;
    wrap.style.setProperty('--pct', pct.toFixed(2));
    wrap.style.setProperty('--scale', scale.toFixed(4));
    range.setAttribute('aria-valuenow', String(Math.round(pos)));
    scaleEl.textContent = scale.toFixed(3);
  }
  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 () {
    pos = Number(range.value);
    vel += KICK;
    paint();
  });

  var targets = [50, 15, 85, 40, 95, 50];
  var seg = 0, posFrom = pos;
  var SEG_MS = 400;
  var segStart = performance.now();
  var last = segStart;

  if (reduce) {
    pos = targets[0];
    range.value = String(pos);
    scale = 1; vel = 0;
    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) % targets.length;
          segStart = now; elapsed = 0; posFrom = pos;
          vel += KICK; // 목표가 바뀔 때마다 튕김 킥
        }
        var target = targets[seg];
        var t = elapsed / SEG_MS;
        pos = posFrom + (target - posFrom) * t;
        range.value = String(Math.round(pos));
      }
      var acc = -K * (scale - 1) - C * vel;
      vel += acc * dt;
      scale += vel * dt;
      paint();
      requestAnimationFrame(step);
    })(segStart);
  }
})();

// RangeSliderSpringThumbOvershoot — vanilla 판(run/334/demo/02-range-slider-spring-thumb-overshoot/index.html)
// 의 React 포트. 값이 바뀌는 순간 썸 스케일에 속도 킥을 넣고, 매 프레임
// accel = -k*(scale-1) - c*velocity 를 적분해 감쇠 진동을 만든다. CSS @keyframes·transition 은
// 없다 — 위치와 스케일 둘 다 requestAnimationFrame 이 매 프레임 다시 계산해 그린다.
import { useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./RangeSliderSpringThumbOvershoot.module.scss";

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

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

const HINT = "값이 바뀔 때마다 스프링-감쇠 방정식으로 썸이 살짝 튕겼다가 안착합니다";
const ARIA_SCENE = "값이 바뀔 때마다 썸이 튕겨 안착하는 스프링 오버슈트 장면";
const ARIA_RANGE = "값 슬라이더";
const UNIT = "스케일 = -k(목표-현재) - c·속도 적분";

const MIN = 0, MAX = 100;
const K = 170, C = 14; // 스프링 상수 · 감쇠 계수 (임계감쇠비 약 0.54 — 12~14% 오버슈트)
const KICK = 9; // 값이 바뀔 때 스케일 속도에 주는 충격량
const TARGETS = [50, 15, 85, 40, 95, 50];
const SEG_MS = 400;

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

  useEffect(() => {
    const wrap = wrapRef.current;
    const range = rangeRef.current;
    const scaleEl = scaleRef.current;
    if (!wrap || !range || !scaleEl) return;

    let pos = 50; // 트랙 위 표시 값(0~100)
    let scale = 1;
    let vel = 0;

    function paint(): void {
      const pct = ((pos - MIN) / (MAX - MIN)) * 100;
      wrap!.style.setProperty("--pct", pct.toFixed(2));
      wrap!.style.setProperty("--scale", scale.toFixed(4));
      range!.setAttribute("aria-valuenow", String(Math.round(pos)));
      scaleEl!.textContent = scale.toFixed(3);
    }
    paint();

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

    let playing = true;
    function stop(): void {
      playing = false;
    }
    function onInput(): void {
      pos = Number(range!.value);
      vel += KICK;
      paint();
    }
    range.addEventListener("pointerdown", stop);
    range.addEventListener("keydown", stop);
    range.addEventListener("input", onInput);

    if (reduce) {
      pos = TARGETS[0];
      range.value = String(pos);
      scale = 1;
      vel = 0;
      paint();
    } else {
      let seg = 0;
      let posFrom = pos;
      let segStart = performance.now();
      let last = segStart;
      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;
            posFrom = pos;
            vel += KICK; // 목표가 바뀔 때마다 튕김 킥
          }
          const target = TARGETS[seg];
          const t = elapsed / SEG_MS;
          pos = posFrom + (target - posFrom) * t;
          range!.value = String(Math.round(pos));
        }
        const acc = -K * (scale - 1) - C * vel;
        vel += acc * dt;
        scale += vel * dt;
        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.so}
        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}>
          <input
            className={styles.range}
            ref={rangeRef}
            type="range"
            min={0}
            max={100}
            step={1}
            defaultValue={50}
            aria-label={ARIA_RANGE}
          />
        </div>
        <p className={styles.meta}>
          <b className={styles.tag} ref={scaleRef}>1.000</b>
          <span className={styles.unit}>{UNIT}</span>
        </p>
      </div>
    </main>
  );
}