03Segment-hover ring — only the arc under the pointer stands out

<main class="stage">
<div class="sh is-demo" id="sh">
  <div class="sh__ring" id="shRing">
    <div class="sh__center">
      <b class="sh__pct" id="shPct">0%</b>
      <span class="sh__label" id="shLabel">CPU</span>
    </div>
  </div>
</div>
</main>

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

// 구간 호버 링 — 계산 겹은 index.html 의 atan2 각도 계산과 360/N 구간 판정(segmentIndexAt)에 있다.
// 여기서는 구간마다 conic-gradient 로 자기 몫의 호만 칠하고 mask-image 로 도넛 모양을 낸 뒤,
// 활성 구간만 scale·filter 로 두께·밝기를 바꾼다.

$duration: $dur-quick;
$easing: $ease-spring;
$color: $subject-blue-light;

@include stage($stage-orange);

.sh { display: flex; align-items: center; justify-content: center; }

.sh__ring {
  position: relative;
  width: 200px;
  height: 200px;
  display: grid;
  place-items: center;
  touch-action: none;
}

.sh__seg {
  position: absolute;
  inset: 0;
  border-radius: 50%;
  background: conic-gradient(from calc(var(--start, 0) * 1deg),
    $color 0deg calc(var(--span, 0) * 1deg), transparent calc(var(--span, 0) * 1deg) 360deg);
  mask-image: radial-gradient(circle, transparent 58%, black 60%, black 84%, transparent 86%);
  -webkit-mask-image: radial-gradient(circle, transparent 58%, black 60%, black 84%, transparent 86%);
  transform: scale(1);
  filter: brightness(.82);
  transition: transform $duration $easing, filter $duration $easing;
}

.sh__seg--active {
  transform: scale(1.08);
  filter: brightness(1.3);
}

.sh__center {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  pointer-events: none;
}
.sh__pct { font-size: 26px; font-weight: 800; color: $subject-ink; line-height: 1; }
.sh__label { font-size: 11px; font-weight: 700; color: rgba($subject-ink, .68); letter-spacing: .04em; }

@media (max-width: 340px) {
  .sh__ring { width: 150px; height: 150px; }
  .sh__pct { font-size: 20px; }
  .sh__label { font-size: 9px; }
}

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

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.sh {
  display: flex;
  align-items: center;
  justify-content: center;
}

.sh__ring {
  position: relative;
  width: 200px;
  height: 200px;
  display: grid;
  place-items: center;
  touch-action: none;
}

.sh__seg {
  position: absolute;
  inset: 0;
  border-radius: 50%;
  background: conic-gradient(from calc(var(--start, 0) * 1deg), #5b8cf8 0deg calc(var(--span, 0) * 1deg), transparent calc(var(--span, 0) * 1deg) 360deg);
  mask-image: radial-gradient(circle, transparent 58%, black 60%, black 84%, transparent 86%);
  -webkit-mask-image: radial-gradient(circle, transparent 58%, black 60%, black 84%, transparent 86%);
  transform: scale(1);
  filter: brightness(0.82);
  transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1), filter 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.sh__seg--active {
  transform: scale(1.08);
  filter: brightness(1.3);
}

.sh__center {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  pointer-events: none;
}

.sh__pct {
  font-size: 26px;
  font-weight: 800;
  color: #17141a;
  line-height: 1;
}

.sh__label {
  font-size: 11px;
  font-weight: 700;
  color: rgba(23, 20, 26, 0.68);
  letter-spacing: 0.04em;
}

@media (max-width: 340px) {
  .sh__ring {
    width: 150px;
    height: 150px;
  }
  .sh__pct {
    font-size: 20px;
  }
  .sh__label {
    font-size: 9px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sh__seg {
    transition: none;
  }
}

(function () {
  var SEGMENTS = [
    { label: 'CPU', pct: 42 },
    { label: 'GPU', pct: 68 },
    { label: 'RAM', pct: 55 },
    { label: 'Network', pct: 27 },
    { label: 'Disk', pct: 81 },
    { label: 'Power', pct: 34 }
  ];
  var N = SEGMENTS.length;
  var GAP_DEG = 3;                    // 구간 사이 틈
  var SEG_DEG = 360 / N - GAP_DEG;    // 구간 하나의 실제 폭
  var LOOP_MS = 2000;

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var root = document.getElementById('sh');
  var ring = document.getElementById('shRing');
  var pctEl = document.getElementById('shPct');
  var labelEl = document.getElementById('shLabel');
  var isDemo = true;

  var segs = SEGMENTS.map(function (s, i) {
    var start = i * 360 / N;
    var el = document.createElement('div');
    el.className = 'sh__seg';
    el.style.setProperty('--start', start);
    el.style.setProperty('--span', SEG_DEG);
    el.setAttribute('aria-hidden', 'true');
    ring.appendChild(el);
    return { el: el, start: start, data: s };
  });

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

  // 계산 겹: 포인터 좌표를 링 중심 기준 각도로 바꾼 뒤(atan2), 어느 구간(360/N 폭)에 속하는지 판정한다.
  function angleAt(clientX, clientY) {
    var r = ring.getBoundingClientRect();
    var cx = r.left + r.width / 2, cy = r.top + r.height / 2;
    var deg = Math.atan2(clientY - cy, clientX - cx) * 180 / Math.PI + 90; // 12시를 0도로
    return ((deg % 360) + 360) % 360;
  }
  function segmentIndexAt(deg) {
    return Math.floor(deg / (360 / N)) % N;
  }

  function setActive(idx) {
    segs.forEach(function (s, i) { s.el.classList.toggle('sh__seg--active', i === idx); });
    var d = SEGMENTS[idx];
    pctEl.textContent = d.pct + '%';
    labelEl.textContent = d.label;
  }

  ring.addEventListener('pointermove', function (e) {
    human();
    setActive(segmentIndexAt(angleAt(e.clientX, e.clientY)));
  });
  ring.addEventListener('pointerleave', function () { human(); });

  // 자동 루프: 가상 포인터가 원을 한 바퀴 도는 것처럼 각도를 연속으로 흘려 같은 판정 함수를 태운다
  function loop(ts) {
    if (isDemo) {
      if (!reduce) {
        var phase = (ts % LOOP_MS) / LOOP_MS;
        setActive(segmentIndexAt(phase * 360));
      } else {
        setActive(0);
      }
    }
    requestAnimationFrame(loop);
  }
  setActive(0);
  requestAnimationFrame(loop);
})();

// SegmentHoverRing — vanilla 판(run/374/demo/03-arc-segment-hover/index.html) 의 React 포트.
// 계산 겹: 포인터 좌표를 링 중심 기준 atan2 각도로 바꾼 뒤(12시를 0도로), 360/N 폭 구간 중 어디에 속하는지 판정한다.
import { useEffect, useRef, useState } from "react";
import styles from "./SegmentHoverRing.module.scss";

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

type Segment = { label: string; pct: number };

const SEGMENTS: Segment[] = [
  { label: "CPU", pct: 42 },
  { label: "GPU", pct: 68 },
  { label: "RAM", pct: 55 },
  { label: "네트워크", pct: 27 },
  { label: "디스크", pct: 81 },
  { label: "전원", pct: 34 },
];
const N = SEGMENTS.length;
const GAP_DEG = 3;
const SEG_DEG = 360 / N - GAP_DEG;
const LOOP_MS = 2000;

export default function SegmentHoverRing() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const ringRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const rafRef = useRef(0) as unknown as Box<number>;
  const [active, setActiveState] = useState(0);

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const root = rootRef.current;
    const ring = ringRef.current;
    if (!root || !ring) return;

    const segEls: HTMLDivElement[] = Array.prototype.slice.call(ring.querySelectorAll("[data-seg]"));
    segEls.forEach(function (el, i) {
      el.style.setProperty("--start", String((i * 360) / N));
      el.style.setProperty("--span", String(SEG_DEG));
    });

    let isDemo = true;

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

    function angleAt(clientX: number, clientY: number) {
      const r = ring!.getBoundingClientRect();
      const cx = r.left + r.width / 2;
      const cy = r.top + r.height / 2;
      const deg = (Math.atan2(clientY - cy, clientX - cx) * 180) / Math.PI + 90;
      return ((deg % 360) + 360) % 360;
    }
    function segmentIndexAt(deg: number) {
      return Math.floor(deg / (360 / N)) % N;
    }

    function setActive(idx: number) {
      segEls.forEach(function (el, i) { el.classList.toggle(styles.segActive, i === idx); });
      setActiveState(idx);
    }

    function onMove(e: PointerEvent) { human(); setActive(segmentIndexAt(angleAt(e.clientX, e.clientY))); }
    function onLeave() { human(); }
    ring.addEventListener("pointermove", onMove);
    ring.addEventListener("pointerleave", onLeave);

    function loop(ts: number) {
      if (isDemo) {
        if (!reduce) {
          const phase = (ts % LOOP_MS) / LOOP_MS;
          setActive(segmentIndexAt(phase * 360));
        } else {
          setActive(0);
        }
      }
      rafRef.current = requestAnimationFrame(loop);
    }
    setActive(0);
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      ring.removeEventListener("pointermove", onMove);
      ring.removeEventListener("pointerleave", onLeave);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  const activeData = SEGMENTS[active];

  return (
    <main className={styles.stage}>
      <div className={styles.sh + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.ring} ref={ringRef}>
          {SEGMENTS.map(function (s, i) {
            return <div key={s.label} data-seg className={styles.seg} aria-hidden="true" />;
          })}
          <div className={styles.center}>
            <b className={styles.pct}>{activeData.pct}%</b>
            <span className={styles.label}>{activeData.label}</span>
          </div>
        </div>
      </div>
    </main>
  );
}