08Spotlight that lights up under the pointer

<main class="stage">
  <div class="sl is-demo" id="sl">
    <div class="sl__view" id="sl-view" tabindex="0" role="img" aria-label="Group photo. Move the spotlight with the arrow keys">
      <div class="sl__dim"></div>
      <div class="sl__lit" id="sl-lit"></div>
    </div>
  </div>
</main>

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

$duration: $dur-base;
$easing: $ease-spring;
$color: $subject-cream;

@include stage($stage-orange);

// 가짜 사진 — 파일 없이 그린 단체 사진. 머리 여섯 개가 줄지어 서 있다
$crowd:
  radial-gradient(circle at 14% 62%, $subject-pink 0 8%, transparent 9%),
  radial-gradient(circle at 31% 54%, $subject-cream 0 8%, transparent 9%),
  radial-gradient(circle at 48% 64%, $subject-mint 0 8%, transparent 9%),
  radial-gradient(circle at 65% 52%, $stage-yellow 0 8%, transparent 9%),
  radial-gradient(circle at 82% 62%, $subject-lilac 0 8%, transparent 9%),
  radial-gradient(circle at 50% 18%, $subject-sky 0 22%, transparent 23%),
  linear-gradient(170deg, #2b2540 0%, $stage-ink 100%);

.sl { position: relative; }

.sl__view {
  position: relative;
  box-sizing: border-box;
  width: 288px;
  height: 168px;
  overflow: hidden;
  border-radius: $r-card;
  background: $stage-ink;
  box-shadow: $shadow-raised;
  cursor: crosshair;
}
.sl__view:focus-visible { outline: 3px solid $subject-ink; outline-offset: 2px; }

.sl__dim,
.sl__lit {
  position: absolute;
  inset: 0;
  background: $crowd;
  background-size: 288px 168px;
}
.sl__dim { filter: grayscale(1) brightness(.44); }

// 선명한 겹은 radial-gradient 로 오린 자리에서만 보인다
.sl__lit {
  -webkit-mask-image: radial-gradient(circle closest-side, #000 0 58%, transparent 100%);
  mask-image: radial-gradient(circle closest-side, #000 0 58%, transparent 100%);
  -webkit-mask-repeat: no-repeat;
  mask-repeat: no-repeat;
  -webkit-mask-size: 128px 128px;
  mask-size: 128px 128px;
  -webkit-mask-position: 12px -6px;
  mask-position: 12px -6px;
}

// ── 자동 루프 (2s) ────────────────────────────────────
// 조명이 세 사람을 훑고 첫 자리로 돌아온다. 끝값이 시작값이라 이음매가 없다
.sl.is-demo .sl__lit {
  animation-name: sl-move;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}

@keyframes sl-move {
  0%   { -webkit-mask-position: 12px -6px;  mask-position: 12px -6px; }
  34%  { -webkit-mask-position: 132px 40px; mask-position: 132px 40px; }
  68%  { -webkit-mask-position: 56px 68px;  mask-position: 56px 68px; }
  100% { -webkit-mask-position: 12px -6px;  mask-position: 12px -6px; }
}

@media (max-width: 360px) {
  .sl__view { height: 160px; }
}

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

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);
}

.sl {
  position: relative;
}

.sl__view {
  position: relative;
  box-sizing: border-box;
  width: 288px;
  height: 168px;
  overflow: hidden;
  border-radius: 16px;
  background: #17141a;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  cursor: crosshair;
}

.sl__view:focus-visible {
  outline: 3px solid #17141a;
  outline-offset: 2px;
}

.sl__dim,
.sl__lit {
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at 14% 62%, #ff9ebb 0 8%, transparent 9%), radial-gradient(circle at 31% 54%, #fff7e6 0 8%, transparent 9%), radial-gradient(circle at 48% 64%, #4cd4a6 0 8%, transparent 9%), radial-gradient(circle at 65% 52%, #ffd23f 0 8%, transparent 9%), radial-gradient(circle at 82% 62%, #b9a0ff 0 8%, transparent 9%), radial-gradient(circle at 50% 18%, #6ec8ff 0 22%, transparent 23%), linear-gradient(170deg, #2b2540 0%, #17141a 100%);
  background-size: 288px 168px;
}

.sl__dim {
  filter: grayscale(1) brightness(0.44);
}

.sl__lit {
  -webkit-mask-image: radial-gradient(circle closest-side, #000 0 58%, transparent 100%);
  mask-image: radial-gradient(circle closest-side, #000 0 58%, transparent 100%);
  -webkit-mask-repeat: no-repeat;
  mask-repeat: no-repeat;
  -webkit-mask-size: 128px 128px;
  mask-size: 128px 128px;
  -webkit-mask-position: 12px -6px;
  mask-position: 12px -6px;
}

.sl.is-demo .sl__lit {
  animation-name: sl-move;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

@keyframes sl-move {
  0% {
    -webkit-mask-position: 12px -6px;
    mask-position: 12px -6px;
  }
  34% {
    -webkit-mask-position: 132px 40px;
    mask-position: 132px 40px;
  }
  68% {
    -webkit-mask-position: 56px 68px;
    mask-position: 56px 68px;
  }
  100% {
    -webkit-mask-position: 12px -6px;
    mask-position: 12px -6px;
  }
}
@media (max-width: 360px) {
  .sl__view {
    height: 160px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sl.is-demo .sl__lit {
    animation: none !important;
  }
}

// 실제 동작: 선명한 겹을 원형 마스크로 오려 보여 준다. 원이 가는 자리만 밝아진다.
var sl = document.getElementById('sl');
var slView = document.getElementById('sl-view');
var slLit = document.getElementById('sl-lit');
var SL_R = 64;
var slX = 76, slY = 58;
function slPaint() {
  var box = slView.getBoundingClientRect();
  slX = Math.min(Math.max(slX, 0), box.width);
  slY = Math.min(Math.max(slY, 0), box.height);
  var pos = (slX - SL_R) + 'px ' + (slY - SL_R) + 'px';
  slLit.style.maskPosition = pos;
  slLit.style.webkitMaskPosition = pos;
}
slView.addEventListener('pointermove', function (e) {
  sl.classList.remove('is-demo');           // 사람이 손대면 자동 루프를 멈춘다
  var box = slView.getBoundingClientRect();
  slX = e.clientX - box.left;
  slY = e.clientY - box.top;
  slPaint();
});
slView.addEventListener('keydown', function (e) {
  var step = { ArrowLeft: [-20, 0], ArrowRight: [20, 0], ArrowUp: [0, -20], ArrowDown: [0, 20] }[e.key];
  if (!step) return;
  e.preventDefault();
  sl.classList.remove('is-demo');
  slX += step[0]; slY += step[1];
  slPaint();
});

import { useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./SpotlightMask.module.scss";

export type SpotlightMaskProps = {
  label?: string;
  /** 마스크 원의 반지름(px). module.scss 의 mask-size 절반과 같아야 한다 */
  radius?: number;
  /** 자동 재생 루프 (갤러리용). 사람이 손대면 꺼진다 */
  demo?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type MaskStyle = CSSProperties & { WebkitMaskPosition?: string; maskPosition?: string };
type PointerEvt = { clientX: number; clientY: number };
type KeyEvt = { key: string; preventDefault: () => void };

const clamp = (v: number, lo: number, hi: number) => Math.min(Math.max(v, lo), hi);

export default function SpotlightMask({
  label = "Group photo. Move the spotlight with the arrow keys",
  radius = 64,
  demo = true,
  duration = 300,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#fff7e6",
}: SpotlightMaskProps) {
  const view = useRef<HTMLDivElement>(null);
  const [live, setLive] = useState(demo);
  const [at, setAt] = useState({ x: 76, y: 58 });

  function move(x: number, y: number) {
    const box = view.current ? view.current.getBoundingClientRect() : null;
    setLive(false);
    setAt({ x: clamp(x, 0, box ? box.width : 288), y: clamp(y, 0, box ? box.height : 168) });
  }

  const pos = `${at.x - radius}px ${at.y - radius}px`;
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  const lit: MaskStyle = { WebkitMaskPosition: pos, maskPosition: pos };

  return (
    <div className={[styles.root, live ? styles.isDemo : ""].join(" ")} style={vars}>
      <div
        className={styles.view}
        ref={view}
        tabIndex={0}
        role="img"
        aria-label={label}
        onPointerMove={(e: PointerEvt) => {
          const box = view.current ? view.current.getBoundingClientRect() : { left: 0, top: 0 };
          move(e.clientX - box.left, e.clientY - box.top);
        }}
        onKeyDown={(e: KeyEvt) => {
          const step: { [k: string]: number[] } = {
            ArrowLeft: [-20, 0], ArrowRight: [20, 0], ArrowUp: [0, -20], ArrowDown: [0, 20],
          };
          if (!step[e.key]) return;
          e.preventDefault();
          move(at.x + step[e.key][0], at.y + step[e.key][1]);
        }}
      >
        <div className={styles.dim} />
        <div className={styles.lit} style={live ? undefined : lit} />
      </div>
    </div>
  );
}