09Inset frame — an outer curve value and an inner curve value sit apart, forming a double border

<main class="stage">
<div class="wrap is-demo" id="wrap">
  <button class="frame" id="frame" type="button" aria-pressed="false" aria-label="Push or pull the inner curve">
    <span class="inner" id="inner">Core</span>
  </button>
  <p class="readout" id="readout" aria-live="polite">Inset 10.0</p>
</div>
</main>

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

// 계산 겹은 index.html 에 있다 — 인셋 산술(안쪽 반경 = 바깥 반경 − 인셋)과 관성 복귀.
@include stage($stage-yellow);

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

.frame {
  appearance: none;
  border: none;
  width: 200px;
  height: 132px;
  padding: $sp-4;
  background: $subject-blue-deep;
  corner-shape: superellipse(3);
  border-radius: $r-card;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: $shadow-raised;

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

.inner {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  background: $subject-mint;
  corner-shape: superellipse(3);
  border-radius: $r-pill;
  color: $subject-ink;
  font-size: 15px;
  font-weight: 800;
  pointer-events: none;
}

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

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

@media (max-width: 340px) {
  .frame { width: 156px; height: 106px; }
  .inner { font-size: 13px; }
}

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

.frame {
  appearance: none;
  border: none;
  width: 200px;
  height: 132px;
  padding: 16px;
  background: #0a4fe8;
  corner-shape: superellipse(3);
  border-radius: 16px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}
.frame:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 3px;
}

.inner {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #4cd4a6;
  corner-shape: superellipse(3);
  border-radius: 999px;
  color: #17141a;
  font-size: 15px;
  font-weight: 800;
  pointer-events: none;
}

@supports not (corner-shape: superellipse(1)) {
  .frame {
    border: 1px solid rgba(23, 20, 26, 0.2);
  }
  .inner {
    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) {
  .frame {
    width: 156px;
    height: 106px;
  }
  .inner {
    font-size: 13px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .frame {
    transition: none;
  }
}

(function () {
  var OUTER_R = 40; // 바깥 프레임의 고정 Radius(px)
  var INSET_MIN = 6; // 안쪽 곡선이 프레임에서 떨어지는 최소 거리(px)
  var INSET_MAX = 22; // 최대 거리(px) — 커질수록 안쪽 곡선이 더 안으로 밀려든다
  var SWEEP_MS = 2400; // 인셋이 한 번 왕복하는 주기
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var SUPPORTS = CSS.supports('corner-shape', 'superellipse(1)');

  var wrap = document.getElementById('wrap');
  var frame = document.getElementById('frame');
  var inner = document.getElementById('inner');
  var readout = document.getElementById('readout');
  var isDemo = true;
  var held = false;
  var heldStart = 0;

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

  // 계산 겹: Inset 산술 — 안쪽 Radius = 바깥 Radius − Inset. 인셋이 커질수록 안쪽 곡선이 더 깎인다
  function innerRadius(inset) { return Math.max(2, OUTER_R - inset); }

  function applyInset(inset) {
    var r = innerRadius(inset);
    if (SUPPORTS) {
      frame.style.cornerShape = 'superellipse(3)';
      inner.style.cornerShape = 'superellipse(3)';
    }
    frame.style.borderRadius = OUTER_R + 'px';
    inner.style.borderRadius = r.toFixed(2) + 'px';
    readout.textContent = 'Inset ' + inset.toFixed(1);
  }

  frame.addEventListener('pointerdown', function () { human(); held = true; heldStart = performance.now(); frame.setAttribute('aria-pressed', 'true'); });
  frame.addEventListener('pointerup', function () { human(); held = false; heldStart = performance.now(); frame.setAttribute('aria-pressed', 'false'); });
  frame.addEventListener('pointerleave', function () { if (held) { held = false; heldStart = performance.now(); frame.setAttribute('aria-pressed', 'false'); } });
  frame.addEventListener('keydown', function (e) { if (e.key === ' ' || e.key === 'Enter') { e.preventDefault(); frame.dispatchEvent(new PointerEvent('pointerdown')); } });
  frame.addEventListener('keyup', function (e) { if (e.key === ' ' || e.key === 'Enter') { e.preventDefault(); frame.dispatchEvent(new PointerEvent('pointerup')); } });

  // 계산 겹: 뗄 때 인셋이 목표로 관성(지수 감쇠)으로 되돌아간다
  var INSET_SPRING_K = 8;
  var insetNow = INSET_MIN;
  function stepInset(ts) {
    var target = held ? INSET_MAX : INSET_MIN;
    var dt = (ts - (stepInset.last || ts)) / 1000;
    stepInset.last = ts;
    var follow = 1 - Math.exp(-INSET_SPRING_K * dt);
    insetNow += (target - insetNow) * follow;
    if (Math.abs(insetNow - target) < 0.01) insetNow = target;
  }

  var start = 0;
  function loop(ts) {
    if (!start) start = ts;
    if (isDemo) {
      if (reduce) {
        insetNow = INSET_MAX;
      } else {
        var t = ((ts - start) % SWEEP_MS) / SWEEP_MS;
        var tri = t < 0.5 ? t * 2 : (1 - t) * 2;
        insetNow = INSET_MIN + (INSET_MAX - INSET_MIN) * tri;
      }
    } else if (!reduce) {
      stepInset(ts);
    }
    applyInset(insetNow);
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

// FrameInset — vanilla 판(run/372/demo/09-corner-shape-frame-inset/index.html) 의 React 포트.
// 인셋 산술(안쪽 반경 = 바깥 반경 − 인셋)과, 뗄 때 목표로 지수 감쇠 관성 복귀.
import { useEffect, useRef } from "react";
import styles from "./FrameInset.module.scss";

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

const OUTER_R = 40; // 바깥 프레임의 고정 반경(px)
const INSET_MIN = 6; // 안쪽 곡선이 프레임에서 떨어지는 최소 거리(px)
const INSET_MAX = 22; // 최대 거리(px) — 커질수록 안쪽 곡선이 더 안으로 밀려든다
const SWEEP_MS = 2400; // 인셋이 한 번 왕복하는 주기
const INSET_SPRING_K = 8; // 뗄 때 목표로 되돌아가는 관성 속도 상수

export default function FrameInset() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const frameRef = useRef(null) as unknown as Box<HTMLButtonElement>;
  const innerRef = useRef(null) as unknown as Box<HTMLSpanElement>;
  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 = CSS.supports("corner-shape", "superellipse(1)");

    const root = rootRef.current;
    const frame = frameRef.current;
    const inner = innerRef.current;
    const readout = readoutRef.current;
    if (!root || !frame || !inner || !readout) return;

    let isDemo = true;
    let held = false;
    let insetNow = INSET_MIN;
    let lastStepTs = 0;

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

    // 계산 겹: 인셋 산술 — 안쪽 반경 = 바깥 반경 − 인셋. 인셋이 커질수록 안쪽 곡선이 더 깎인다
    function innerRadius(inset: number) { return Math.max(2, OUTER_R - inset); }

    function applyInset(inset: number) {
      const r = innerRadius(inset);
      if (SUPPORTS) {
        (frame!.style as any).cornerShape = "superellipse(3)";
        (inner!.style as any).cornerShape = "superellipse(3)";
      }
      frame!.style.borderRadius = OUTER_R + "px";
      inner!.style.borderRadius = r.toFixed(2) + "px";
      readout!.textContent = "인셋 " + inset.toFixed(1);
    }

    function onPointerDown() { human(); held = true; frame!.setAttribute("aria-pressed", "true"); }
    function onPointerUp() { human(); held = false; frame!.setAttribute("aria-pressed", "false"); }
    function onPointerLeave() { if (held) { held = false; frame!.setAttribute("aria-pressed", "false"); } }
    function onKeyDown(e: KeyboardEvent) { if (e.key === " " || e.key === "Enter") { e.preventDefault(); onPointerDown(); } }
    function onKeyUp(e: KeyboardEvent) { if (e.key === " " || e.key === "Enter") { e.preventDefault(); onPointerUp(); } }
    frame.addEventListener("pointerdown", onPointerDown);
    frame.addEventListener("pointerup", onPointerUp);
    frame.addEventListener("pointerleave", onPointerLeave);
    frame.addEventListener("keydown", onKeyDown);
    frame.addEventListener("keyup", onKeyUp);

    // 계산 겹: 뗄 때 인셋이 목표로 관성(지수 감쇠)으로 되돌아간다
    function stepInset(ts: number) {
      const target = held ? INSET_MAX : INSET_MIN;
      const dt = (ts - (lastStepTs || ts)) / 1000;
      lastStepTs = ts;
      const follow = 1 - Math.exp(-INSET_SPRING_K * dt);
      insetNow += (target - insetNow) * follow;
      if (Math.abs(insetNow - target) < 0.01) insetNow = target;
    }

    let start = 0;
    function loop(ts: number) {
      if (!start) start = ts;
      if (isDemo) {
        if (reduce) {
          insetNow = INSET_MAX;
        } else {
          const t = ((ts - start) % SWEEP_MS) / SWEEP_MS;
          const tri = t < 0.5 ? t * 2 : (1 - t) * 2;
          insetNow = INSET_MIN + (INSET_MAX - INSET_MIN) * tri;
        }
      } else if (!reduce) {
        stepInset(ts);
      }
      applyInset(insetNow);
      rafRef.current = requestAnimationFrame(loop);
    }
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      frame.removeEventListener("pointerdown", onPointerDown);
      frame.removeEventListener("pointerup", onPointerUp);
      frame.removeEventListener("pointerleave", onPointerLeave);
      frame.removeEventListener("keydown", onKeyDown);
      frame.removeEventListener("keyup", onKeyUp);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.wrap + " " + styles.isDemo} ref={rootRef}>
        <button
          className={styles.frame}
          ref={frameRef}
          type="button"
          aria-pressed="false"
          aria-label="안쪽 곡선 밀기/당기기"
        >
          <span className={styles.inner} ref={innerRef}>코어</span>
        </button>
        <p className={styles.readout} ref={readoutRef} aria-live="polite">인셋 10.0</p>
      </div>
    </main>
  );
}