01Press-value overshoot — the pressed value passes its target value and swings back, repeating while the swing shrinks

<main class="stage">
<div class="bso is-demo" id="bso">
  <button class="bso__btn" id="bsoBtn" type="button">Submit</button>
  <p class="bso__val"><span>Depth value</span><b id="bsoVal">0.0px</b></p>
</div>
</main>

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

// 계산 겹(스프링-감쇠 적분)은 JS 에 있다 — 여기는 정적 배치만.
@include stage($stage-paper);

.stage { position: relative; }

.bso {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-4;
}

.bso__btn {
  border: 0;
  border-radius: $r-control;
  padding: $sp-4 $sp-8;
  background: $subject-blue-deep;
  color: $subject-cream;
  font-size: 16px;
  font-weight: 700;
  line-height: 1.2;
  cursor: pointer;
  transform-origin: 50% 0;
  box-shadow: $shadow-raised;
}

.bso__val {
  display: flex;
  align-items: center;
  gap: $sp-2;
  color: $subject-ink;
  font-size: 13px;

  span { opacity: .64; }
  b { font-weight: 700; min-width: 52px; }
}

@media (max-width: 340px) {
  .bso__btn { padding: $sp-3 $sp-6; font-size: 15px; }
}

@media (prefers-reduced-motion: reduce) {
  .bso__btn { transition: none !important; }
}

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

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

.stage {
  position: relative;
}

.bso {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}

.bso__btn {
  border: 0;
  border-radius: 12px;
  padding: 16px 32px;
  background: #0a4fe8;
  color: #fff7e6;
  font-size: 16px;
  font-weight: 700;
  line-height: 1.2;
  cursor: pointer;
  transform-origin: 50% 0;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.bso__val {
  display: flex;
  align-items: center;
  gap: 8px;
  color: #17141a;
  font-size: 13px;
}
.bso__val span {
  opacity: 0.64;
}
.bso__val b {
  font-weight: 700;
  min-width: 52px;
}

@media (max-width: 340px) {
  .bso__btn {
    padding: 12px 24px;
    font-size: 15px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .bso__btn {
    transition: none !important;
  }
}

(function () {
  var root = document.getElementById('bso');
  var btn = document.getElementById('bsoBtn');
  var val = document.getElementById('bsoVal');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  // 계산 겹: 스프링-감쇠 방정식 accel = -(K/MASS)*(depth-target) - (C/MASS)*vel.
  // 목표 값을 지나쳤다가 되돌아오는 오버슈트는 감쇠비(zeta = C/(2*sqrt(K*MASS)))가
  // 1보다 작은 저감쇠(underdamped) 상태라 생긴다 — zeta 를 낮출수록 반동 폭이 커진다.
  var K = 300, C = 7, MASS = 1, PRESS_DEPTH = 14;
  var depth = 0, vel = 0, target = 0, last = 0, raf = null;

  function paint() {
    var scale = 1 - depth / 340;
    btn.style.transform = 'translateY(' + depth.toFixed(2) + 'px) scale(' + scale.toFixed(4) + ')';
    val.textContent = depth.toFixed(1) + 'px';
  }
  function tick(now) {
    var dt = Math.min((now - last) / 1000, 0.032);
    last = now;
    var accel = (-K * (depth - target) - C * vel) / MASS;
    vel += accel * dt;
    depth += vel * dt;
    paint();
    raf = requestAnimationFrame(tick);
  }
  function start() {
    if (raf === null) { last = performance.now(); raf = requestAnimationFrame(tick); }
  }
  function press(p) {
    if (reduce) { depth = p; vel = 0; target = p; paint(); return; }
    target = p;
    start();
  }

  function wireReal() {
    btn.addEventListener('pointerdown', function () { root.classList.remove('is-demo'); stopAutoplay(); press(PRESS_DEPTH); });
    window.addEventListener('pointerup', function () { press(0); });
    btn.addEventListener('pointercancel', function () { press(0); });
  }
  wireReal();
  paint();

  // 자동 루프: 누름 350ms 뒤 뗌으로 같은 press() 스프링 경로를 반복 재현한다.
  var autoTimer = null, autoDown = null;
  function autoTick() { press(PRESS_DEPTH); autoDown = setTimeout(function () { press(0); }, 350); }
  function stopAutoplay() {
    if (autoTimer) { clearInterval(autoTimer); autoTimer = null; }
    if (autoDown) { clearTimeout(autoDown); autoDown = null; }
  }
  if (!reduce) { autoTick(); autoTimer = setInterval(autoTick, 1500); }
})();

import { useEffect, useRef } from "react";
import styles from "./ButtonPhysicsSpringOvershoot.module.scss";

export type ButtonPhysicsSpringOvershootProps = {
  color?: string;
};

export default function ButtonPhysicsSpringOvershoot({
  color = "#0a4fe8",
}: ButtonPhysicsSpringOvershootProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const btn = root.querySelector<HTMLButtonElement>(`.${styles.btn}`);
    const val = root.querySelector<HTMLElement>(`.${styles.valNum}`);
    if (!btn || !val) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    // 계산 겹: 스프링-감쇠 방정식 accel = -(K/MASS)*(depth-target) - (C/MASS)*vel.
    // 목표 값을 지나쳤다가 되돌아오는 오버슈트는 감쇠비(zeta = C/(2*sqrt(K*MASS)))가
    // 1보다 작은 저감쇠(underdamped) 상태라 생긴다 — zeta 를 낮출수록 반동 폭이 커진다.
    const K = 300, C = 7, MASS = 1, PRESS_DEPTH = 14;
    let depth = 0, vel = 0, target = 0, last = 0, raf: number | null = null;

    function paint() {
      const scale = 1 - depth / 340;
      btn!.style.transform = "translateY(" + depth.toFixed(2) + "px) scale(" + scale.toFixed(4) + ")";
      val!.textContent = depth.toFixed(1) + "px";
    }
    function tick(now: number) {
      const dt = Math.min((now - last) / 1000, 0.032);
      last = now;
      const accel = (-K * (depth - target) - C * vel) / MASS;
      vel += accel * dt;
      depth += vel * dt;
      paint();
      raf = requestAnimationFrame(tick);
    }
    function start() { if (raf === null) { last = performance.now(); raf = requestAnimationFrame(tick); } }
    function press(p: number) {
      if (reduce) { depth = p; vel = 0; target = p; paint(); return; }
      target = p;
      start();
    }

    function onPointerDown() { stopAutoplay(); press(PRESS_DEPTH); }
    function onPointerUp() { press(0); }
    btn.addEventListener("pointerdown", onPointerDown);
    window.addEventListener("pointerup", onPointerUp);
    btn.addEventListener("pointercancel", onPointerUp);
    paint();

    let autoTimer: number | null = null, autoDown: number | null = null;
    function autoTick() { press(PRESS_DEPTH); autoDown = window.setTimeout(() => { press(0); }, 350); }
    function stopAutoplay() {
      if (autoTimer !== null) { window.clearInterval(autoTimer); autoTimer = null; }
      if (autoDown !== null) { window.clearTimeout(autoDown); autoDown = null; }
    }
    if (!reduce) { autoTick(); autoTimer = window.setInterval(autoTick, 1500); }

    return () => {
      stopAutoplay();
      if (raf !== null) cancelAnimationFrame(raf);
      btn.removeEventListener("pointerdown", onPointerDown);
      window.removeEventListener("pointerup", onPointerUp);
      btn.removeEventListener("pointercancel", onPointerUp);
    };
  }, []);

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.bso}>
        <button className={styles.btn} type="button" style={{ background: color }}>제출하기</button>
        <p className={styles.val}><span className={styles.valLabel}>깊이 값</span><b className={styles.valNum}>0.0px</b></p>
      </div>
    </div>
  );
}