06Hover morph — the corner curve value interpolates between the idle state and the hover state

<main class="stage">
<div class="wrap is-demo" id="wrap">
  <button class="card" id="card" type="button" aria-pressed="false" aria-label="Hover to change the card shape"></button>
  <p class="readout" id="readout" aria-live="polite">Interpolation ratio 0%</p>
</div>
</main>

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

// 계산 겹은 index.html 에 있다 — 목표 비율로 순간 이동하지 않고 지수 감쇠 lerp 로 따라붙는다.
@include stage($stage-yellow);

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

.card {
  appearance: none;
  border: none;
  width: 168px;
  height: 108px;
  background: $subject-blue-deep;
  border-radius: $r-card;
  cursor: pointer;
  box-shadow: $shadow-raised;

  &:hover { box-shadow: $shadow-press; }
  &:focus-visible { outline: 2px solid $subject-ink; outline-offset: 3px; }
}

@supports not (corner-shape: bevel) {
  .card { border: 1px solid rgba($subject-ink, .2); }
}

.readout {
  margin: 0;
  color: $subject-ink;
  font-size: 13px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .card { width: 130px; height: 88px; }
}

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

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

.card {
  appearance: none;
  border: none;
  width: 168px;
  height: 108px;
  background: #0a4fe8;
  border-radius: 16px;
  cursor: pointer;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}
.card:hover {
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}
.card:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 3px;
}

@supports not (corner-shape: bevel) {
  .card {
    border: 1px solid rgba(23, 20, 26, 0.2);
  }
}
.readout {
  margin: 0;
  color: #17141a;
  font-size: 13px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .card {
    width: 130px;
    height: 88px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .card {
    transition: none;
  }
}

(function () {
  var ROUND_R = 48; // 대기 상태(둥근 원형)의 Radius 상한(px)
  var BEVEL_R = 6; // 호버 상태(각진 베벨)의 Radius 하한(px)
  var LERP_K = 9; // 목표 비율로 붙는 속도 상수 — 클수록 빨리 따라붙는다
  var AUTO_MS = 2000; // 자동 루프에서 대기·호버를 오가는 주기
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var SUPPORTS_ROUND = CSS.supports('corner-shape', 'round');
  var SUPPORTS_BEVEL = CSS.supports('corner-shape', 'bevel');

  var wrap = document.getElementById('wrap');
  var card = document.getElementById('card');
  var readout = document.getElementById('readout');
  var isDemo = true;
  var target = 0;
  var ratio = 0;

  function human() { if (isDemo) { wrap.classList.remove('is-demo'); isDemo = false; } }

  function setTarget(v) { target = v; }
  card.addEventListener('pointerenter', function () { human(); setTarget(1); });
  card.addEventListener('pointerleave', function () { human(); setTarget(0); });
  card.addEventListener('focus', function () { human(); setTarget(1); });
  card.addEventListener('blur', function () { human(); setTarget(0); });
  card.addEventListener('click', function () { human(); card.setAttribute('aria-pressed', String(target === 1)); });

  // 계산 겹: 비율 값을 목표로 순간 이동시키지 않고 지수 감쇠(dt 기반 관성 lerp)로 붙인다 — 두 모양 사이 보간 비율이다
  var last = 0;
  function stepRatio(ts) {
    var dt = last ? (ts - last) / 1000 : 0;
    last = ts;
    var follow = 1 - Math.exp(-LERP_K * dt);
    ratio += (target - ratio) * follow;
    if (Math.abs(ratio - target) < 0.001) ratio = target;
  }

  function applyMorph() {
    var r = ROUND_R + (BEVEL_R - ROUND_R) * ratio;
    var shape = ratio < 0.5 ? (SUPPORTS_ROUND ? 'round' : null) : (SUPPORTS_BEVEL ? 'bevel' : null);
    if (shape) card.style.cornerShape = shape;
    card.style.borderRadius = r.toFixed(2) + 'px';
    readout.textContent = 'Interpolation ratio ' + Math.round(ratio * 100) + '%';
  }

  var start = 0;
  function loop(ts) {
    if (!start) start = ts;
    if (isDemo) {
      if (reduce) {
        target = 1; // 계산은 유지, 시간 축소 대신 호버 목표 상태로 즉시 고정
      } else {
        var t = ((ts - start) % AUTO_MS) / AUTO_MS;
        target = t < 0.5 ? 0 : 1;
      }
    }
    if (reduce) {
      ratio = target;
    } else {
      stepRatio(ts);
    }
    applyMorph();
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

// MorphHover — vanilla 판(run/372/demo/06-corner-shape-morph-hover/index.html) 의 React 포트.
// 비율 값을 목표로 순간 이동시키지 않고 지수 감쇠(dt 기반 관성 lerp)로 붙인다.
import { useEffect, useRef } from "react";
import styles from "./MorphHover.module.scss";

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

const ROUND_R = 48; // 대기 상태(둥근 원형)의 반경 상한(px)
const BEVEL_R = 6; // 호버 상태(각진 베벨)의 반경 하한(px)
const LERP_K = 9; // 목표 비율로 붙는 속도 상수 — 클수록 빨리 따라붙는다
const AUTO_MS = 2000; // 자동 루프에서 대기·호버를 오가는 주기

export default function MorphHover() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const cardRef = useRef(null) as unknown as Box<HTMLButtonElement>;
  const readoutRef = useRef(null) as unknown as Box<HTMLParagraphElement>;
  const rafRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const SUPPORTS_ROUND = CSS.supports("corner-shape", "round");
    const SUPPORTS_BEVEL = CSS.supports("corner-shape", "bevel");

    const root = rootRef.current;
    const card = cardRef.current;
    const readout = readoutRef.current;
    if (!root || !card || !readout) return;

    let isDemo = true;
    let target = 0;
    let ratio = 0;

    function human() { if (isDemo) { root!.classList.remove(styles.isDemo); isDemo = false; } }

    function setTarget(v: number) { target = v; }
    function onEnter() { human(); setTarget(1); }
    function onLeave() { human(); setTarget(0); }
    function onFocus() { human(); setTarget(1); }
    function onBlur() { human(); setTarget(0); }
    function onClick() { human(); card!.setAttribute("aria-pressed", String(target === 1)); }
    card.addEventListener("pointerenter", onEnter);
    card.addEventListener("pointerleave", onLeave);
    card.addEventListener("focus", onFocus);
    card.addEventListener("blur", onBlur);
    card.addEventListener("click", onClick);

    // 계산 겹: 비율 값을 목표로 순간 이동시키지 않고 지수 감쇠(dt 기반 관성 lerp)로 붙인다 — 두 모양 사이 보간 비율이다
    let last = 0;
    function stepRatio(ts: number) {
      const dt = last ? (ts - last) / 1000 : 0;
      last = ts;
      const follow = 1 - Math.exp(-LERP_K * dt);
      ratio += (target - ratio) * follow;
      if (Math.abs(ratio - target) < 0.001) ratio = target;
    }

    function applyMorph() {
      const r = ROUND_R + (BEVEL_R - ROUND_R) * ratio;
      const shape = ratio < 0.5 ? (SUPPORTS_ROUND ? "round" : null) : (SUPPORTS_BEVEL ? "bevel" : null);
      if (shape) (card!.style as any).cornerShape = shape;
      card!.style.borderRadius = r.toFixed(2) + "px";
      readout!.textContent = "보간 비율 " + Math.round(ratio * 100) + "%";
    }

    let start = 0;
    function loop(ts: number) {
      if (!start) start = ts;
      if (isDemo) {
        if (reduce) {
          target = 1;
        } else {
          const t = ((ts - start) % AUTO_MS) / AUTO_MS;
          target = t < 0.5 ? 0 : 1;
        }
      }
      if (reduce) {
        ratio = target;
      } else {
        stepRatio(ts);
      }
      applyMorph();
      rafRef.current = requestAnimationFrame(loop);
    }
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      card.removeEventListener("pointerenter", onEnter);
      card.removeEventListener("pointerleave", onLeave);
      card.removeEventListener("focus", onFocus);
      card.removeEventListener("blur", onBlur);
      card.removeEventListener("click", onClick);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.wrap + " " + styles.isDemo} ref={rootRef}>
        <button
          className={styles.card}
          ref={cardRef}
          type="button"
          aria-pressed="false"
          aria-label="올려서 카드 모양 바꾸기"
        />
        <p className={styles.readout} ref={readoutRef} aria-live="polite">보간 비율 0%</p>
      </div>
    </main>
  );
}