06Refraction follows cursor

<main class="stage">
  <div class="rh-panel rh-focal is-demo">
    <span class="rh-panel__title">Hover the glass</span>
    <span class="rh-panel__desc">Specular light follows the cursor</span>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$easing: linear;
$color: $subject-cream;

// 커서 좌표 — 퍼센트로 등록해야 is-demo 의 키프레임이 값을 보간한다
@property --mx { syntax: '<percentage>'; inherits: true; initial-value: 50%; }
@property --my { syntax: '<percentage>'; inherits: true; initial-value: 50%; }

@include stage($stage-yellow);

.rh-panel {
  position: relative;
  overflow: hidden;
  box-sizing: border-box;
  width: min(300px, 86vw);
  aspect-ratio: 300 / 190;
  border-radius: $r-card;
  background: rgba(255, 255, 255, .16);
  border: 1px solid rgba(255, 255, 255, .4);
  backdrop-filter: blur(14px) saturate(160%);
  -webkit-backdrop-filter: blur(14px) saturate(160%);
  box-shadow: $shadow-press;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  gap: $sp-1;
  padding: $sp-4;
  color: $subject-ink;
  font: 600 12px/1.3 -apple-system, "Segoe UI", sans-serif;
  --mx: 50%;
  --my: 35%;
}
.rh-panel__title { position: relative; z-index: 1; font-size: 13px; font-weight: 700; }
.rh-panel__desc { position: relative; z-index: 1; opacity: .75; font-weight: 500; }

// 실사용: 진짜 pointermove 가 --mx·--my 를 갱신한다(위 <script>)
.rh-panel::before {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(120px 80px at var(--mx) var(--my), $color 0%, transparent 70%);
  opacity: .7;
  pointer-events: none;
}

// 데모 루프: is-demo 는 --mx·--my 를 keyframes 로 원을 그리며 돌려 캡처 (실 JS 와 별개 경로, 공존 가능)
@keyframes rh-drift {
  0%   { --mx: 15%; --my: 20%; }
  25%  { --mx: 85%; --my: 15%; }
  50%  { --mx: 85%; --my: 85%; }
  75%  { --mx: 15%; --my: 80%; }
  100% { --mx: 15%; --my: 20%; }
}
.rh-panel.is-demo { animation: rh-drift $duration $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .rh-panel.is-demo { animation: none !important; }
}

@property --mx {
  syntax: "<percentage>";
  inherits: true;
  initial-value: 50%;
}
@property --my {
  syntax: "<percentage>";
  inherits: true;
  initial-value: 50%;
}
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);
}

.rh-panel {
  position: relative;
  overflow: hidden;
  box-sizing: border-box;
  width: min(300px, 86vw);
  aspect-ratio: 300/190;
  border-radius: 16px;
  background: rgba(255, 255, 255, 0.16);
  border: 1px solid rgba(255, 255, 255, 0.4);
  backdrop-filter: blur(14px) saturate(160%);
  -webkit-backdrop-filter: blur(14px) saturate(160%);
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  gap: 4px;
  padding: 16px;
  color: #17141a;
  font: 600 12px/1.3 -apple-system, "Segoe UI", sans-serif;
  --mx: 50%;
  --my: 35%;
}

.rh-panel__title {
  position: relative;
  z-index: 1;
  font-size: 13px;
  font-weight: 700;
}

.rh-panel__desc {
  position: relative;
  z-index: 1;
  opacity: 0.75;
  font-weight: 500;
}

.rh-panel::before {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(120px 80px at var(--mx) var(--my), #fff7e6 0%, transparent 70%);
  opacity: 0.7;
  pointer-events: none;
}

@keyframes rh-drift {
  0% {
    --mx: 15%;
    --my: 20%;
  }
  25% {
    --mx: 85%;
    --my: 15%;
  }
  50% {
    --mx: 85%;
    --my: 85%;
  }
  75% {
    --mx: 15%;
    --my: 80%;
  }
  100% {
    --mx: 15%;
    --my: 20%;
  }
}
.rh-panel.is-demo {
  animation: rh-drift 2s linear infinite;
}

@media (prefers-reduced-motion: reduce) {
  .rh-panel.is-demo {
    animation: none !important;
  }
}

var panel = document.querySelector('.rh-panel');
panel.addEventListener('pointermove', function (e) {
  var r = panel.getBoundingClientRect();
  var x = ((e.clientX - r.left) / r.width * 100).toFixed(1) + '%';
  var y = ((e.clientY - r.top) / r.height * 100).toFixed(1) + '%';
  panel.style.setProperty('--mx', x);
  panel.style.setProperty('--my', y);
});

import { CSSProperties, PointerEvent, useCallback, useRef } from "react";
import styles from "./RefractionHover.module.scss";

type Vars = CSSProperties & {
  "--color"?: string;
  "--mx"?: string;
  "--my"?: string;
};

export interface RefractionHoverProps {
  color?: string;
}

// 실사용: 진짜 pointermove 가 --mx·--my 를 갱신한다. 하이라이트는 CSS 만으로 그 좌표를 그린다
export default function RefractionHover({ color = "#fff7e6" }: RefractionHoverProps) {
  const panelRef = useRef<HTMLDivElement>(null);

  const handleMove = useCallback((e: PointerEvent<HTMLDivElement>) => {
    const el = panelRef.current;
    if (!el) return;
    const r = el.getBoundingClientRect();
    const x = (((e.clientX - r.left) / r.width) * 100).toFixed(1) + "%";
    const y = (((e.clientY - r.top) / r.height) * 100).toFixed(1) + "%";
    el.style.setProperty("--mx", x);
    el.style.setProperty("--my", y);
  }, []);

  const style: Vars = { "--color": color };

  return (
    <div className={styles.panel} style={style} ref={panelRef} onPointerMove={handleMove}>
      <span className={styles.title}>Hover the glass</span>
      <span className={styles.desc}>Specular light follows the cursor</span>
    </div>
  );
}