02Button That Gradually Grows as the Distance Value Shrinks

<main class="stage">
<div class="sl is-demo" id="sl">
  <p class="sl__badge" id="slBadge">Distance value 100%</p>
  <div class="sl__scene" id="slScene">
    <button class="sl__btn" id="slBtn" type="button">Add</button>
  </div>
</div>
</main>

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

// 핵심: 거리 값을 스프링 방정식(강성·감쇠)에 흘려 버튼 크기·들림을 연속으로 바꾼다.
// 이진적 켜짐·꺼짐이 아니라 목표를 살짝 넘겼다가 정착하는 계산 한 겹(오버슛)을 더했다.

$duration: $dur-loop;
$easing: $ease-lerp-settle;
$color: $subject-ink;

@include stage($stage-yellow);

.sl {
  display: grid;
  gap: $sp-4;
  justify-items: center;
}

.sl__badge {
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .12);
  color: $subject-ink;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.sl__scene {
  position: relative;
  padding: $sp-10;
  --tone-p: 0;
}

.sl__scene::before {
  content: '';
  position: absolute;
  inset: 0;
  margin: auto;
  width: 220px;
  height: 140px;
  border-radius: $r-control;
  background: radial-gradient(circle, rgba($subject-blue-deep, .4), transparent 70%);
  transform: scale(calc(0.55 + var(--tone-p) * 0.7));
  opacity: var(--tone-p);
  pointer-events: none;
  z-index: 0;
}

.sl__btn {
  position: relative;
  z-index: 1;
  border: 0;
  cursor: pointer;
  padding: $sp-4 $sp-8;
  border-radius: $r-control;
  background: $color;
  color: $subject-cream;
  font-size: 16px;
  font-weight: 700;
  transform-origin: center;
  will-change: transform, box-shadow;
}

.sl__btn:focus-visible {
  outline: 2px solid $subject-cream;
  outline-offset: 3px;
}

@media (max-width: 340px) {
  .sl__scene { padding: $sp-6; }
  .sl__btn { padding: $sp-3 $sp-6; font-size: 14px; }
}

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

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);
}

.sl {
  display: grid;
  gap: 16px;
  justify-items: center;
}

.sl__badge {
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.12);
  color: #17141a;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.sl__scene {
  position: relative;
  padding: 40px;
  --tone-p: 0;
}

.sl__scene::before {
  content: "";
  position: absolute;
  inset: 0;
  margin: auto;
  width: 220px;
  height: 140px;
  border-radius: 12px;
  background: radial-gradient(circle, rgba(10, 79, 232, 0.4), transparent 70%);
  transform: scale(calc(0.55 + var(--tone-p) * 0.7));
  opacity: var(--tone-p);
  pointer-events: none;
  z-index: 0;
}

.sl__btn {
  position: relative;
  z-index: 1;
  border: 0;
  cursor: pointer;
  padding: 16px 32px;
  border-radius: 12px;
  background: #17141a;
  color: #fff7e6;
  font-size: 16px;
  font-weight: 700;
  transform-origin: center;
  will-change: transform, box-shadow;
}

.sl__btn:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 3px;
}

@media (max-width: 340px) {
  .sl__scene {
    padding: 24px;
  }
  .sl__btn {
    padding: 12px 24px;
    font-size: 14px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sl__btn {
    transition: none;
  }
}

(function () {
  var PROX_RADIUS_PX = 170;
  var SL_SCALE_MAX = 0.08;
  var SL_LIFT_MAX_PX = 6;
  // 스프링 방정식(강성·감쇠) — lerp 보다 한 겹 더한 관성: 목표를 살짝 넘겼다가 정착한다.
  var STIFFNESS = 0.22;
  var DAMPING = 0.72;

  var root = document.getElementById('sl');
  var scene = document.getElementById('slScene');
  var btn = document.getElementById('slBtn');
  var badge = document.getElementById('slBadge');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function clamp(v, lo, hi) { return Math.max(lo, Math.min(hi, v)); }

  var targetP = 0;
  var pos = 0;
  var vel = 0;
  var hasPointer = false;

  function distanceToButton(x, y) {
    var r = btn.getBoundingClientRect();
    var cx = r.left + r.width / 2;
    var cy = r.top + r.height / 2;
    return Math.hypot(x - cx, y - cy);
  }

  function render(p) {
    var scale = 1 + p * SL_SCALE_MAX;
    var lift = p * SL_LIFT_MAX_PX;
    var depth = 8 + p * 18;
    btn.style.transform = 'translateY(' + (-lift).toFixed(2) + 'px) scale(' + scale.toFixed(4) + ')';
    btn.style.boxShadow = '0 ' + depth.toFixed(1) + 'px ' + (depth * 1.6).toFixed(1) + 'px rgba(23,20,26,' + (0.18 + p * 0.18).toFixed(2) + ')';
    // 계산 레이어: 스프링 오버슛(p) 을 배경 톤(그림자 뒤 글로우)에도 같은 값으로 전파한다.
    var tone = clamp(p, 0, 1.15);
    scene.style.setProperty('--tone-p', tone.toFixed(3));
    badge.textContent = 'Distance value ' + Math.round((1 - clamp(p, 0, 1)) * 100) + '%';
  }

  function springStep(target) {
    var force = (target - pos) * STIFFNESS;
    vel = (vel + force) * DAMPING;
    pos += vel;
  }

  function syntheticOffset(t) {
    var ang = t * 1.4 + 0.6;
    var rad = 110 * (1 + Math.cos(t * Math.PI));
    return [Math.cos(ang) * rad, Math.sin(ang) * rad];
  }

  var startTime = null;
  function loop(now) {
    if (startTime === null) { startTime = now; }
    var t = (now - startTime) / 1000;
    if (!hasPointer && !reduce) {
      var off = syntheticOffset(t);
      var d = Math.hypot(off[0], off[1]);
      targetP = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
    }
    springStep(targetP);
    render(clamp(pos, -0.2, 1.2));
    requestAnimationFrame(loop);
  }

  scene.addEventListener('pointermove', function (e) {
    hasPointer = true;
    root.classList.remove('is-demo');
    var d = distanceToButton(e.clientX, e.clientY);
    targetP = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
    if (reduce) { pos = targetP; render(pos); }
  });
  scene.addEventListener('pointerleave', function () {
    hasPointer = false;
    targetP = 0;
    if (reduce) { pos = 0; render(0); }
  });
  btn.addEventListener('focus', function () {
    hasPointer = true;
    targetP = 1;
    if (reduce) { pos = 1; render(1); }
  });
  btn.addEventListener('blur', function () {
    hasPointer = false;
    targetP = 0;
    if (reduce) { pos = 0; render(0); }
  });

  if (reduce) {
    render(0);
  } else {
    requestAnimationFrame(loop);
  }
})();

// ProximityScaleLiftButton — vanilla 판(run/408/demo/02-btn-proximity-scale-lift-hover/index.html) 의 React 포트.
// 거리 값을 스프링 방정식(강성 STIFFNESS·감쇠 DAMPING)에 흘려 목표를 살짝 넘겼다가 정착하는
// 오버슛 한 겹을 더한다 — 단순 lerp 보다 한 계산 층이 깊다.
import { useEffect, useRef, useState } from "react";
import type { PointerEvent as ReactPointerEvent } from "react";
import styles from "./ProximityScaleLiftButton.module.scss";

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

const PROX_RADIUS_PX = 170;
const SL_SCALE_MAX = 0.08;
const SL_LIFT_MAX_PX = 6;
const STIFFNESS = 0.22;
const DAMPING = 0.72;

function clamp(v: number, lo: number, hi: number): number {
  return Math.max(lo, Math.min(hi, v));
}

function syntheticOffset(t: number): [number, number] {
  const ang = t * 1.4 + 0.6;
  const rad = 110 * (1 + Math.cos(t * Math.PI));
  return [Math.cos(ang) * rad, Math.sin(ang) * rad];
}

export default function ProximityScaleLiftButton() {
  const sceneRef = useRef<HTMLDivElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);
  const badgeRef = useRef<HTMLParagraphElement | null>(null);
  const targetPRef = useRef<number>(0) as Box<number>;
  const posRef = useRef<number>(0) as Box<number>;
  const velRef = useRef<number>(0) as Box<number>;
  const hasPointerRef = useRef<boolean>(false) as Box<boolean>;
  const frameRef = useRef<number>(0) as Box<number>;
  const t0Ref = useRef<number>(0) as Box<number>;
  const [demo, setDemo] = useState(true);
  const [reduce, setReduce] = useState(false);

  function render(p: number): void {
    const btn = btnRef.current;
    const badge = badgeRef.current;
    const scene = sceneRef.current;
    if (!btn || !badge || !scene) return;
    const scale = 1 + p * SL_SCALE_MAX;
    const lift = p * SL_LIFT_MAX_PX;
    const depth = 8 + p * 18;
    btn.style.transform = "translateY(" + (-lift).toFixed(2) + "px) scale(" + scale.toFixed(4) + ")";
    btn.style.boxShadow = "0 " + depth.toFixed(1) + "px " + (depth * 1.6).toFixed(1) + "px rgba(23,20,26," + (0.18 + p * 0.18).toFixed(2) + ")";
    // 계산 레이어: 스프링 오버슛 값(p, 1 을 넘나든다)을 장면 배경 글로우 크기·불투명도에도 전파한다.
    const tone = clamp(p, 0, 1.15);
    scene.style.setProperty("--tone-p", tone.toFixed(3));
    badge.textContent = "거리 값 " + Math.round((1 - clamp(p, 0, 1)) * 100) + "%";
  }

  function springStep(target: number): void {
    const force = (target - posRef.current) * STIFFNESS;
    velRef.current = (velRef.current + force) * DAMPING;
    posRef.current += velRef.current;
  }

  function distanceToButton(x: number, y: number): number {
    const btn = btnRef.current;
    if (!btn) return PROX_RADIUS_PX;
    const r = btn.getBoundingClientRect();
    const cx = r.left + r.width / 2;
    const cy = r.top + r.height / 2;
    return Math.hypot(x - cx, y - cy);
  }

  useEffect(() => {
    setReduce(window.matchMedia("(prefers-reduced-motion: reduce)").matches);
  }, []);

  useEffect(() => {
    if (reduce) {
      render(0);
      return;
    }
    function loop(now: number): void {
      if (t0Ref.current === 0) t0Ref.current = now;
      const t = (now - t0Ref.current) / 1000;
      if (!hasPointerRef.current) {
        const off = syntheticOffset(t);
        const d = Math.hypot(off[0], off[1]);
        targetPRef.current = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
      }
      springStep(targetPRef.current);
      render(clamp(posRef.current, -0.2, 1.2));
      frameRef.current = requestAnimationFrame(loop);
    }
    frameRef.current = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(frameRef.current);
  }, [reduce]);

  function onPointerMove(event: ReactPointerEvent<HTMLDivElement>): void {
    hasPointerRef.current = true;
    setDemo(false);
    const d = distanceToButton(event.clientX, event.clientY);
    targetPRef.current = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
    if (reduce) { posRef.current = targetPRef.current; render(posRef.current); }
  }

  function onPointerLeave(): void {
    hasPointerRef.current = false;
    targetPRef.current = 0;
    if (reduce) { posRef.current = 0; render(0); }
  }

  function onFocus(): void {
    hasPointerRef.current = true;
    targetPRef.current = 1;
    if (reduce) { posRef.current = 1; render(1); }
  }

  function onBlur(): void {
    hasPointerRef.current = false;
    targetPRef.current = 0;
    if (reduce) { posRef.current = 0; render(0); }
  }

  const cls = [styles.sl, demo ? styles.isDemo : ""].filter(Boolean).join(" ");
  return (
    <main className={styles.stage}>
      <div className={cls}>
        <p className={styles.badge} ref={badgeRef}>거리 값 100%</p>
        <div className={styles.scene} ref={sceneRef} onPointerMove={onPointerMove} onPointerLeave={onPointerLeave}>
          <button className={styles.btn} ref={btnRef} type="button" onFocus={onFocus} onBlur={onBlur}>담기</button>
        </div>
      </div>
    </main>
  );
}