07メニュー項目の間をばねで滑る強調ピル

<main class="stage">
<div class="pm is-demo" id="pm" data-demo="1">
  <p class="pm__live" data-r="live" aria-live="off" aria-atomic="true"></p>
  <div class="pm__menu" data-r="menu">
    <i class="pm__pill" data-r="pill"><i class="pm__sheen" data-r="sheen"></i></i>
    <button class="pm__it" data-r="it" type="button">プロフィール</button>
    <button class="pm__it" data-r="it" type="button">通知</button>
    <button class="pm__it" data-r="it" type="button">料金</button>
    <button class="pm__it pm__it--tall" data-r="it" type="button">ログアウト</button>
  </div>
</div>
</main>

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

// 핵심: 알약은 항목마다 켜졌다 꺼지지 않고 하나가 위치와 높이를 스프링으로 따라 움직이며, 바뀔 때마다 빛줄기가 한 번 훑는다.

@include stage($stage-ink);

.pm {
  position: relative;
  box-sizing: border-box;
  overflow: hidden;
  width: min(100%, 440px);
  height: min(252px, calc(100vh - 2 * clamp(8px, 4vw, 24px)));
  border-radius: $r-card;
  background: rgba($subject-cream, .07);
  color: $subject-cream;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}
.pm b { font-weight: 800; font-variant-numeric: tabular-nums; }
.pm__live {
  position: absolute;
  left: $sp-3;
  top: $sp-2;
  margin: 0;
  z-index: 9;
  color: $tick-mute;
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
  pointer-events: none;
}
.pm button { font-family: inherit; }
.pm button:focus-visible { outline: 3px solid $subject-pink; outline-offset: 2px; }


.pm__menu {
  position: absolute;
  left: 50%;
  top: 22px;
  box-sizing: border-box;
  width: min(192px, calc(100% - 24px));
  margin-left: calc(min(192px, 100% - 24px) / -2);
  padding: $sp-1 $sp-2;
  border-radius: $r-card;
  background: $tick-panel;
  box-shadow: $shadow-raised;
}
.pm__pill {
  position: absolute;
  left: $sp-2;
  right: $sp-2;
  top: 0;
  height: 32px;
  overflow: hidden;
  border-radius: $r-control;
  background: $subject-lilac;
  will-change: transform;
}
.pm__sheen {
  position: absolute;
  left: 0;
  top: 0;
  height: 100%;
  background: linear-gradient(90deg, transparent, rgba($subject-cream, .7), transparent);
  pointer-events: none;
}
.pm__it {
  position: relative;
  display: block;
  box-sizing: border-box;
  width: 100%;
  height: 32px;
  padding: 0 $sp-3;
  border: 0;
  border-radius: $r-control;
  background: transparent;
  color: $subject-cream;
  font-size: 13px;
  line-height: 20px;
  font-weight: 700;
  text-align: left;
  cursor: pointer;
}
.pm__it--tall { height: 40px; }
.pm__it[data-on] { color: $subject-ink; }
@media (prefers-reduced-motion: reduce) {
  .pm__pill { will-change: auto; }
  .pm__sheen { display: none; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.pm {
  position: relative;
  box-sizing: border-box;
  overflow: hidden;
  width: min(100%, 440px);
  height: min(252px, 100vh - 2 * clamp(8px, 4vw, 24px));
  border-radius: 16px;
  background: rgba(255, 247, 230, 0.07);
  color: #fff7e6;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}

.pm b {
  font-weight: 800;
  font-variant-numeric: tabular-nums;
}

.pm__live {
  position: absolute;
  left: 12px;
  top: 8px;
  margin: 0;
  z-index: 9;
  color: #9a93a6;
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
  pointer-events: none;
}

.pm button {
  font-family: inherit;
}

.pm button:focus-visible {
  outline: 3px solid #ff9ebb;
  outline-offset: 2px;
}

.pm__menu {
  position: absolute;
  left: 50%;
  top: 22px;
  box-sizing: border-box;
  width: min(192px, 100% - 24px);
  margin-left: calc(min(192px, 100% - 24px) / -2);
  padding: 4px 8px;
  border-radius: 16px;
  background: #231f28;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.pm__pill {
  position: absolute;
  left: 8px;
  right: 8px;
  top: 0;
  height: 32px;
  overflow: hidden;
  border-radius: 12px;
  background: #b9a0ff;
  will-change: transform;
}

.pm__sheen {
  position: absolute;
  left: 0;
  top: 0;
  height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255, 247, 230, 0.7), transparent);
  pointer-events: none;
}

.pm__it {
  position: relative;
  display: block;
  box-sizing: border-box;
  width: 100%;
  height: 32px;
  padding: 0 12px;
  border: 0;
  border-radius: 12px;
  background: transparent;
  color: #fff7e6;
  font-size: 13px;
  line-height: 20px;
  font-weight: 700;
  text-align: left;
  cursor: pointer;
}

.pm__it--tall {
  height: 40px;
}

.pm__it[data-on] {
  color: #17141a;
}

@media (prefers-reduced-motion: reduce) {
  .pm__pill {
    will-change: auto;
  }
  .pm__sheen {
    display: none;
  }
}

(function () {
    const root = document.getElementById("pm");
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    let acc = 0;
    let clock = 0;
    const offs = [];
    const live = root.querySelector("[data-r=live]");
    function q(sel) {
        return root.querySelector(sel);
    }
    function clamp(v, lo, hi) {
        return Math.max(lo, Math.min(hi, v));
    }
    function seg(t, a, b) {
        const c = clamp((t - a) / (b - a), 0, 1);
        return c * c * (3 - 2 * c);
    }
    function on(el, type, fn) {
        el.addEventListener(type, fn);
        offs.push(() => el.removeEventListener(type, fn));
    }
    function stopDemo() {
        if (!demo)
            return;
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
        live.setAttribute("aria-live", "polite");
    }
    if (reduce)
        live.setAttribute("aria-live", "polite");
    let shown = "";
    function say(s) {
        if (s === shown)
            return;
        shown = s;
        live.textContent = s;
    }
    function makeRng(seed) {
        let s = seed >>> 0;
        return () => {
            s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
            return s / 4294967296;
        };
    }
    function local(e) {
        const r = root.getBoundingClientRect();
        return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function sync() {
        if (reduce) {
            snap();
            render();
        }
    }
    // 기법: 강조 알약의 위치와 높이를 각각 스프링(PILL_STIFF, PILL_DAMP)으로 풀어 가리킨 항목을 쫓게 하고, 항목이 바뀔 때마다 SHEEN_W 폭의 빛줄기를 한 번 훑는다.
    const PILL_STIFF = 0.18;
    const PILL_DAMP = 0.72;
    const SHEEN_W = 48;
    const ITEM_H = 32;
    const SHEEN_MS = 420;
    const STEP_MS = 420;
    const SEQ = [0, 2, 3, 1, 0];
    const menu = q("[data-r=menu]");
    const pill = q("[data-r=pill]");
    const sheen = q("[data-r=sheen]");
    const its = Array.from(root.querySelectorAll("[data-r=it]"));
    let want = 0;
    let prevWant = -1;
    let py = 0;
    let ph = ITEM_H;
    let vy = 0;
    let vh = 0;
    let sheenT = SHEEN_MS;
    let placed = false;
    function goalY() {
        return its[want].offsetTop;
    }
    function goalH() {
        return its[want].offsetHeight || ITEM_H;
    }
    function tick(ms) {
        if (demo)
            want = SEQ[Math.floor(Math.max(0, ms - 200) / STEP_MS) % SEQ.length];
        if (!placed)
            snap();
        if (want !== prevWant) {
            prevWant = want;
            sheenT = 0;
        }
        vy = (vy + (goalY() - py) * PILL_STIFF) * PILL_DAMP;
        py += vy;
        vh = (vh + (goalH() - ph) * PILL_STIFF) * PILL_DAMP;
        ph += vh;
        sheenT = Math.min(SHEEN_MS, sheenT + 1000 / 60);
    }
    function snap() {
        py = goalY();
        ph = goalH();
        vy = 0;
        vh = 0;
        prevWant = want;
        sheenT = SHEEN_MS;
        placed = true;
    }
    function render() {
        pill.style.height = ph.toFixed(1) + "px";
        pill.style.transform = "translate3d(0," + py.toFixed(1) + "px,0)";
        const wide = pill.clientWidth;
        const p = sheenT / SHEEN_MS;
        sheen.style.width = SHEEN_W + "px";
        sheen.style.transform = "translate3d(" + (-SHEEN_W + p * (wide + SHEEN_W)).toFixed(1) + "px,0,0) skewX(-18deg)";
        sheen.style.opacity = p >= 1 ? "0" : "1";
        for (let i = 0; i < its.length; i += 1) {
            if (i === want)
                its[i].setAttribute("data-on", "1");
            else
                its[i].removeAttribute("data-on");
        }
        say("item " + (want + 1) + "  y " + Math.round(py) + "  h " + Math.round(ph));
    }
    function pick(i) {
        stopDemo();
        want = i;
        sync();
    }
    its.forEach((el, i) => {
        on(el, "pointerenter", () => pick(i));
        on(el, "focus", () => pick(i));
        on(el, "keydown", (e) => {
            const d = e.key === "ArrowDown" ? 1 : e.key === "ArrowUp" ? -1 : 0;
            if (d === 0)
                return;
            e.preventDefault();
            const n = (i + d + its.length) % its.length;
            its[n].focus({ preventScroll: true });
        });
    });
    snap();
    const FRAME_MS = 1000 / 60;
    function frame(ts) {
        if (t0 < 0) {
            t0 = ts;
            last = ts;
        }
        acc += Math.min(100, ts - last);
        last = ts;
        let n = 0;
        while (acc >= FRAME_MS && n < 6) {
            clock += FRAME_MS;
            tick(clock);
            acc -= FRAME_MS;
            n += 1;
        }
        if (n === 6)
            acc = 0;
        render();
        raf = requestAnimationFrame(frame);
    }
    const ro = new ResizeObserver(() => sync());
    ro.observe(root);
    if (reduce) {
        stopDemo();
        snap();
        render();
    }
    else {
        raf = requestAnimationFrame(frame);
    }
    return () => {
        cancelAnimationFrame(raf);
        offs.forEach((f) => f());
        ro.disconnect();
    };
})();

// RovingSpotlightMenu - vanilla 판(07-pm-menu-roving-spotlight) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./RovingSpotlightMenu.module.scss";

export default function RovingSpotlightMenu() {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const rootEl = rootRef.current;
    if (!rootEl) return;
    const root: HTMLElement = rootEl;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    let acc = 0;
    let clock = 0;
    const offs: Array<() => void> = [];
    const live = root.querySelector("[data-r=live]") as HTMLElement;

    function q<T extends Element>(sel: string): T {
      return root.querySelector(sel) as T;
    }
    function clamp(v: number, lo: number, hi: number): number {
      return Math.max(lo, Math.min(hi, v));
    }
    function seg(t: number, a: number, b: number): number {
      const c = clamp((t - a) / (b - a), 0, 1);
      return c * c * (3 - 2 * c);
    }
    function on(el: EventTarget, type: string, fn: (e: any) => void): void {
      el.addEventListener(type, fn);
      offs.push(() => el.removeEventListener(type, fn));
    }
    function stopDemo(): void {
      if (!demo) return;
      demo = false;
      root.removeAttribute("data-demo");
      root.classList.remove("is-demo");
      live.setAttribute("aria-live", "polite");
    }
    if (reduce) live.setAttribute("aria-live", "polite");
    let shown = "";
    function say(s: string): void {
      if (s === shown) return;
      shown = s;
      live.textContent = s;
    }
    function makeRng(seed: number): () => number {
      let s = seed >>> 0;
      return () => {
        s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
        return s / 4294967296;
      };
    }
    function local(e: PointerEvent): { x: number; y: number } {
      const r = root.getBoundingClientRect();
      return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function sync(): void {
      if (reduce) {
        snap();
        render();
      }
    }

    // 기법: 강조 알약의 위치와 높이를 각각 스프링(PILL_STIFF, PILL_DAMP)으로 풀어 가리킨 항목을 쫓게 하고, 항목이 바뀔 때마다 SHEEN_W 폭의 빛줄기를 한 번 훑는다.
    const PILL_STIFF = 0.18;
    const PILL_DAMP = 0.72;
    const SHEEN_W = 48;
    const ITEM_H = 32;
    const SHEEN_MS = 420;
    const STEP_MS = 420;
    const SEQ = [0, 2, 3, 1, 0];
    const menu = q<HTMLElement>("[data-r=menu]");
    const pill = q<HTMLElement>("[data-r=pill]");
    const sheen = q<HTMLElement>("[data-r=sheen]");
    const its = Array.from(root.querySelectorAll("[data-r=it]")) as HTMLElement[];
    let want = 0;
    let prevWant = -1;
    let py = 0;
    let ph = ITEM_H;
    let vy = 0;
    let vh = 0;
    let sheenT = SHEEN_MS;
    let placed = false;

    function goalY(): number {
      return its[want].offsetTop;
    }
    function goalH(): number {
      return its[want].offsetHeight || ITEM_H;
    }
    function tick(ms: number): void {
      if (demo) want = SEQ[Math.floor(Math.max(0, ms - 200) / STEP_MS) % SEQ.length];
      if (!placed) snap();
      if (want !== prevWant) {
        prevWant = want;
        sheenT = 0;
      }
      vy = (vy + (goalY() - py) * PILL_STIFF) * PILL_DAMP;
      py += vy;
      vh = (vh + (goalH() - ph) * PILL_STIFF) * PILL_DAMP;
      ph += vh;
      sheenT = Math.min(SHEEN_MS, sheenT + 1000 / 60);
    }
    function snap(): void {
      py = goalY();
      ph = goalH();
      vy = 0;
      vh = 0;
      prevWant = want;
      sheenT = SHEEN_MS;
      placed = true;
    }
    function render(): void {
      pill.style.height = ph.toFixed(1) + "px";
      pill.style.transform = "translate3d(0," + py.toFixed(1) + "px,0)";
      const wide = pill.clientWidth;
      const p = sheenT / SHEEN_MS;
      sheen.style.width = SHEEN_W + "px";
      sheen.style.transform = "translate3d(" + (-SHEEN_W + p * (wide + SHEEN_W)).toFixed(1) + "px,0,0) skewX(-18deg)";
      sheen.style.opacity = p >= 1 ? "0" : "1";
      for (let i = 0; i < its.length; i += 1) {
        if (i === want) its[i].setAttribute("data-on", "1");
        else its[i].removeAttribute("data-on");
      }
      say("item " + (want + 1) + "  y " + Math.round(py) + "  h " + Math.round(ph));
    }
    function pick(i: number): void {
      stopDemo();
      want = i;
      sync();
    }
    its.forEach((el, i) => {
      on(el, "pointerenter", () => pick(i));
      on(el, "focus", () => pick(i));
      on(el, "keydown", (e: KeyboardEvent) => {
        const d = e.key === "ArrowDown" ? 1 : e.key === "ArrowUp" ? -1 : 0;
        if (d === 0) return;
        e.preventDefault();
        const n = (i + d + its.length) % its.length;
        its[n].focus({ preventScroll: true });
      });
    });

    snap();

    const FRAME_MS = 1000 / 60;
    function frame(ts: number): void {
      if (t0 < 0) {
        t0 = ts;
        last = ts;
      }
      acc += Math.min(100, ts - last);
      last = ts;
      let n = 0;
      while (acc >= FRAME_MS && n < 6) {
        clock += FRAME_MS;
        tick(clock);
        acc -= FRAME_MS;
        n += 1;
      }
      if (n === 6) acc = 0;
      render();
      raf = requestAnimationFrame(frame);
    }
    const ro = new ResizeObserver(() => sync());
    ro.observe(root);
    if (reduce) {
      stopDemo();
      snap();
      render();
    } else {
      raf = requestAnimationFrame(frame);
    }
    return () => {
      cancelAnimationFrame(raf);
      offs.forEach((f) => f());
      ro.disconnect();
    };

  }, []);

  return (
    <main className={styles["stage"]}>
      <div ref={rootRef} className={styles["pm"] + " is-demo"} data-demo="1">
        <p className={styles["pm__live"]} data-r="live" aria-live="off" aria-atomic="true"></p>
        <div className={styles["pm__menu"]} data-r="menu">
          <i className={styles["pm__pill"]} data-r="pill"><i className={styles["pm__sheen"]} data-r="sheen"></i></i>
          <button className={styles["pm__it"]} data-r="it" type="button">프로필</button>
          <button className={styles["pm__it"]} data-r="it" type="button">알림</button>
          <button className={styles["pm__it"]} data-r="it" type="button">요금</button>
          <button className={styles["pm__it"] + " " + styles["pm__it--tall"]} data-r="it" type="button">로그아웃</button>
        </div>
      </div>
    </main>
  );
}