01Magnifier lens that follows the pointer

<main class="stage">
  <div class="mg is-demo" id="mg">
    <div class="mg__photo" id="mg-photo" tabindex="0" role="img" aria-label="Checked fabric. Move the magnifier with the arrow keys">
      <div class="mg__lens" id="mg-lens" aria-hidden="true"></div>
    </div>
  </div>
</main>

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

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

@include stage($stage-ink);

// 가짜 사진 — 파일 없이 그라디언트만으로 짠 격자 원단.
// 렌즈가 같은 배경 스택을 2.4배 크기로 다시 그리므로 두 겹이 정확히 겹친다.
$photo:
  repeating-linear-gradient(0deg, rgba(23, 20, 26, .26) 0 1.6%, transparent 1.6% 4%),
  repeating-linear-gradient(90deg, rgba(23, 20, 26, .26) 0 1.6%, transparent 1.6% 4%),
  radial-gradient(circle at 74% 24%, rgba(255, 247, 230, .5) 0 6%, transparent 7%),
  linear-gradient(135deg, $stage-orange 0%, $stage-yellow 36%, $subject-mint 68%, $subject-blue 100%);
$pw: 288px;
$ph: 168px;
$zoom: 2.4;
$lens: 88px;

.mg { position: relative; }

.mg__photo {
  position: relative;
  box-sizing: border-box;
  width: $pw;
  height: $ph;
  overflow: hidden;
  border-radius: $r-card;
  background: $photo;
  background-size: $pw $ph;
  cursor: crosshair;
}
.mg__photo:focus-visible { outline: 3px solid $color; outline-offset: 2px; }

.mg__lens {
  position: absolute;
  left: 0;
  top: 0;
  width: $lens;
  height: $lens;
  border: 3px solid $color;
  border-radius: 50%;
  background: $photo;
  background-size: $pw * $zoom $ph * $zoom;
  background-position: -138.4px -100px;   // 기본 자리 = 루프 1번 지점
  box-shadow: $shadow-raised;
  transform: translate(32px, 16px);
  pointer-events: none;
}

// ── 자동 루프 (2s) ────────────────────────────────────
// 세 지점을 P1 → P2 → P3 → P2 → P1 으로 왕복한다. 끝점이 시작점이라 이음매가 없다.
.mg.is-demo .mg__lens {
  animation-name: mg-lens;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}

@keyframes mg-lens {
  0%   { transform: translate(32px, 16px);   background-position: -138.4px -100px; }
  28%  { transform: translate(106px, 68px);  background-position: -316px -224.8px; }
  52%  { transform: translate(188px, 18px);  background-position: -512.8px -104.8px; }
  78%  { transform: translate(106px, 68px);  background-position: -316px -224.8px; }
  100% { transform: translate(32px, 16px);   background-position: -138.4px -100px; }
}

@media (prefers-reduced-motion: reduce) {
  .mg.is-demo .mg__lens { 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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.mg {
  position: relative;
}

.mg__photo {
  position: relative;
  box-sizing: border-box;
  width: 288px;
  height: 168px;
  overflow: hidden;
  border-radius: 16px;
  background: repeating-linear-gradient(0deg, rgba(23, 20, 26, 0.26) 0 1.6%, transparent 1.6% 4%), repeating-linear-gradient(90deg, rgba(23, 20, 26, 0.26) 0 1.6%, transparent 1.6% 4%), radial-gradient(circle at 74% 24%, rgba(255, 247, 230, 0.5) 0 6%, transparent 7%), linear-gradient(135deg, #ff4d1f 0%, #ffd23f 36%, #4cd4a6 68%, #2f6df6 100%);
  background-size: 288px 168px;
  cursor: crosshair;
}

.mg__photo:focus-visible {
  outline: 3px solid #fff7e6;
  outline-offset: 2px;
}

.mg__lens {
  position: absolute;
  left: 0;
  top: 0;
  width: 88px;
  height: 88px;
  border: 3px solid #fff7e6;
  border-radius: 50%;
  background: repeating-linear-gradient(0deg, rgba(23, 20, 26, 0.26) 0 1.6%, transparent 1.6% 4%), repeating-linear-gradient(90deg, rgba(23, 20, 26, 0.26) 0 1.6%, transparent 1.6% 4%), radial-gradient(circle at 74% 24%, rgba(255, 247, 230, 0.5) 0 6%, transparent 7%), linear-gradient(135deg, #ff4d1f 0%, #ffd23f 36%, #4cd4a6 68%, #2f6df6 100%);
  background-size: 691.2px 403.2px;
  background-position: -138.4px -100px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transform: translate(32px, 16px);
  pointer-events: none;
}

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

@keyframes mg-lens {
  0% {
    transform: translate(32px, 16px);
    background-position: -138.4px -100px;
  }
  28% {
    transform: translate(106px, 68px);
    background-position: -316px -224.8px;
  }
  52% {
    transform: translate(188px, 18px);
    background-position: -512.8px -104.8px;
  }
  78% {
    transform: translate(106px, 68px);
    background-position: -316px -224.8px;
  }
  100% {
    transform: translate(32px, 16px);
    background-position: -138.4px -100px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .mg.is-demo .mg__lens {
    animation: none !important;
  }
}

// 실제 동작: 포인터가 가리키는 지점을 2.4배로 키워 렌즈 안에 보여 준다.
var mg = document.getElementById('mg');
var mgPhoto = document.getElementById('mg-photo');
var mgLens = document.getElementById('mg-lens');
var MG_ZOOM = 2.4;
var mgX = 76, mgY = 60;
function mgPaint() {
  var box = mgPhoto.getBoundingClientRect();
  var half = mgLens.offsetWidth / 2;
  mgX = Math.min(Math.max(mgX, half), box.width - half);
  mgY = Math.min(Math.max(mgY, half), box.height - half);
  mgLens.style.transform = 'translate(' + (mgX - half) + 'px,' + (mgY - half) + 'px)';
  mgLens.style.backgroundPosition = -(mgX * MG_ZOOM - half) + 'px ' + -(mgY * MG_ZOOM - half) + 'px';
}
mgPhoto.addEventListener('pointermove', function (e) {
  mg.classList.remove('is-demo');          // 사람이 손대면 자동 루프를 멈춘다
  var box = mgPhoto.getBoundingClientRect();
  mgX = e.clientX - box.left;
  mgY = e.clientY - box.top;
  mgPaint();
});
mgPhoto.addEventListener('keydown', function (e) {
  var step = { ArrowLeft: [-16, 0], ArrowRight: [16, 0], ArrowUp: [0, -16], ArrowDown: [0, 16] }[e.key];
  if (!step) return;
  e.preventDefault();
  mg.classList.remove('is-demo');
  mgX += step[0]; mgY += step[1];
  mgPaint();
});

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

export type MagnifierLensProps = {
  label?: string;
  /** 렌즈 안 배율. style.scss 의 $zoom 과 같은 값이어야 두 겹이 겹친다 */
  zoom?: 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 PointerEvt = { clientX: number; clientY: number };
type KeyEvt = { key: string; preventDefault: () => void };

const HALF = 44;
const clamp = (v: number, lo: number, hi: number) => Math.min(Math.max(v, lo), hi);

export default function MagnifierLens({
  label = "Checked fabric. Move the magnifier with the arrow keys",
  zoom = 2.4,
  demo = true,
  duration = 220,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#fff7e6",
}: MagnifierLensProps) {
  const photo = useRef<HTMLDivElement>(null);
  const [live, setLive] = useState(demo);
  const [at, setAt] = useState({ x: 76, y: 60 });

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

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  const lens: CSSProperties = {
    transform: `translate(${at.x - HALF}px,${at.y - HALF}px)`,
    backgroundPosition: `${-(at.x * zoom - HALF)}px ${-(at.y * zoom - HALF)}px`,
  };

  return (
    <div className={[styles.root, live ? styles.isDemo : ""].join(" ")} style={vars}>
      <div
        className={styles.photo}
        ref={photo}
        tabIndex={0}
        role="img"
        aria-label={label}
        onPointerMove={(e: PointerEvt) => {
          const box = photo.current ? photo.current.getBoundingClientRect() : { left: 0, top: 0 };
          move(e.clientX - box.left, e.clientY - box.top);
        }}
        onKeyDown={(e: KeyEvt) => {
          const step: { [k: string]: number[] } = {
            ArrowLeft: [-16, 0], ArrowRight: [16, 0], ArrowUp: [0, -16], ArrowDown: [0, 16],
          };
          if (!step[e.key]) return;
          e.preventDefault();
          move(at.x + step[e.key][0], at.y + step[e.key][1]);
        }}
      >
        <div className={styles.lens} aria-hidden="true" style={live ? undefined : lens} />
      </div>
    </div>
  );
}