08Hover image preview — with a ribbon tail

<main class="stage">
<div class="iv is-demo" id="iv">
  <div class="iv__scene" role="img" aria-label="The picture of the hovered row floats up and chases the cursor">
    <ul class="iv__list">
      <li><button class="iv__row" type="button" data-scene="night">Lanterns in the night sky</button></li>
      <li><button class="iv__row" type="button" data-scene="sea">An afternoon by the sea</button></li>
      <li><button class="iv__row" type="button" data-scene="forest">Morning in the forest</button></li>
    </ul>
    <div class="iv__preview" id="ivPreview" aria-hidden="true">
      <span class="iv__art iv__art--night"></span>
      <span class="iv__art iv__art--sea"></span>
      <span class="iv__art iv__art--forest"></span>
      <span class="iv__ribbon" id="ivRibbon">Lanterns in the night sky</span>
    </div>
  </div>
  <p class="iv__hint">Hover a row and its picture follows you around</p>
</div>
</main>

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

// 오버 시 이미지 프리뷰 — 줄에 올리면 그 항목의 그림(그라디언트 장면)이 커서를 lerp(0.13)로 쫓아
// 떠오르고, 이동 방향에 따라 rotate 로 살짝 기울며 리본 이름표가 붙어 따라온다.
// 격자 미리보기(.is-demo)는 그림이 세 줄을 차례로 찾아다니는 루프를 @keyframes 로 돌린다.

$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-ink;

@include stage($stage-paper);

.iv { display: grid; justify-items: center; gap: $sp-3; width: 100%; }

.iv__scene {
  position: relative; overflow: hidden;
  display: flex; align-items: center;
  width: 100%; height: clamp(110px, 32vh, 160px);
  border: 3px solid $color; border-radius: $r-card;
  background: $subject-cream;
}

.iv__list { list-style: none; margin: 0; padding: 0 $sp-4; display: grid; gap: $sp-2; }

.iv__row {
  appearance: none;
  padding: $sp-1 $sp-2;
  background: transparent; border: 0;
  color: $color;
  font-family: inherit; font-weight: 700; font-size: clamp(12px, 3.2vw, 15px); line-height: 1.5;
  text-align: left; white-space: nowrap;
  border-radius: $r-sm;
  cursor: pointer;
}
.iv__row:hover { text-decoration: underline; text-decoration-thickness: 3px; text-underline-offset: 4px; }
.iv__row:focus-visible { outline: 3px solid $subject-blue; outline-offset: 2px; }

// 프리뷰 그림 — 커서를 쫓는 150x110 카드. 장면 세 개를 겹쳐 두고 opacity 로 갈아 낀다
.iv__preview {
  position: absolute; left: 0; top: 0;
  width: 150px; height: 110px;
  border: 3px solid $color; border-radius: $r-sm;
  background: $stage-paper;
  box-shadow: $shadow-raised;
  will-change: transform;
}
.iv__art {
  position: absolute; inset: 0;
  border-radius: $r-xs;
  transition: opacity $dur-quick $ease-out;
}
// 세 장면 — 사진 대신 색면으로 밤하늘·바다·숲을 나타낸다 (외부 파일 0)
.iv__art--night {
  background:
    radial-gradient(circle at 78% 24%, rgba($stage-yellow, .95) 0 7%, rgba($stage-yellow, 0) 9%),
    radial-gradient(circle at 22% 70%, rgba($stage-yellow, .8) 0 4%, rgba($stage-yellow, 0) 6%),
    linear-gradient(180deg, $subject-blue-deep 0%, $subject-ink 100%);
}
.iv__art--sea {
  background:
    radial-gradient(circle at 72% 20%, rgba($stage-paper, .9) 0 9%, rgba($stage-paper, 0) 14%),
    linear-gradient(180deg, $subject-sky 0%, $subject-sky 52%, $subject-mint 52%, $subject-mint 100%);
}
.iv__art--forest {
  background:
    radial-gradient(circle at 26% 26%, rgba($stage-yellow, .95) 0 10%, rgba($stage-yellow, 0) 16%),
    linear-gradient(180deg, $subject-mint 0%, $chart-3 130%);
}
// 달·해는 그라디언트 원으로, 숲 능선은 반투명 삼각형 겹침으로
.iv__art--forest::before {
  content: ""; position: absolute; left: 0; right: 0; bottom: 0;
  height: 46%;
  background: linear-gradient(135deg, transparent 0 18%, rgba($subject-ink, .8) 18% 32%, transparent 32% 48%, rgba($subject-ink, .8) 48% 66%, transparent 66%);
}

// 리본 이름표 — 그림 왼쪽 위에 붙는다 (붙는 지점이 있는 요소).
// 파란 면은 크림 글자가 5.98:1 이 되는 한 단계 진한 쪽을 쓴다
.iv__ribbon {
  position: absolute; left: -3px; top: $sp-2;
  padding: $sp-1 $sp-2;
  background: $subject-blue-deep;
  color: $subject-cream;
  font-weight: 700; font-size: clamp(9px, 2.4vw, 10px); line-height: 1.3;
  border-radius: 0 $r-xs $r-xs 0;
}

.iv__hint { margin: 0; color: $color; font-weight: 700; font-size: clamp(9px, 2.4vw, 11px); }

// ── 미리보기 루프: 그림이 세 줄을 차례로 찾아가며 살짝 기울었다 편다
.iv.is-demo .iv__preview { animation: ivTour $duration $easing infinite; }

@keyframes ivTour {
  0%, 8%    { transform: translate3d(196px, 18px, 0) rotate(-3deg); }
  30%, 38%  { transform: translate3d(232px, 48px, 0) rotate(3deg); }
  58%, 66%  { transform: translate3d(210px, 78px, 0) rotate(-2deg); }
  88%, 100% { transform: translate3d(196px, 18px, 0) rotate(-3deg); }
}

@media (max-width: 340px) {
  .iv { gap: $sp-2; }
  .iv__scene { height: clamp(96px, 28vh, 130px); }
  .iv__preview { width: 120px; height: 88px; }
  .iv__list { padding: 0 $sp-2; }
  .iv.is-demo .iv__preview { animation-name: ivTourNarrow; }
}

@keyframes ivTourNarrow {
  0%, 8%    { transform: translate3d(148px, 14px, 0) rotate(-3deg); }
  30%, 38%  { transform: translate3d(168px, 38px, 0) rotate(3deg); }
  58%, 66%  { transform: translate3d(152px, 62px, 0) rotate(-2deg); }
  88%, 100% { transform: translate3d(148px, 14px, 0) rotate(-3deg); }
}

@media (prefers-reduced-motion: reduce) {
  .iv.is-demo .iv__preview { animation: none !important; }
  // reduce 에서는 그림이 오른쪽 고정 자리에 바로 서 있다
  .iv.is-demo .iv__preview { transform: translate3d(196px, 40px, 0) rotate(0deg) !important; }
  .iv__art { transition: none; }
}

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

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

.iv {
  display: grid;
  justify-items: center;
  gap: 12px;
  width: 100%;
}

.iv__scene {
  position: relative;
  overflow: hidden;
  display: flex;
  align-items: center;
  width: 100%;
  height: clamp(110px, 32vh, 160px);
  border: 3px solid #17141a;
  border-radius: 16px;
  background: #fff7e6;
}

.iv__list {
  list-style: none;
  margin: 0;
  padding: 0 16px;
  display: grid;
  gap: 8px;
}

.iv__row {
  appearance: none;
  padding: 4px 8px;
  background: transparent;
  border: 0;
  color: #17141a;
  font-family: inherit;
  font-weight: 700;
  font-size: clamp(12px, 3.2vw, 15px);
  line-height: 1.5;
  text-align: left;
  white-space: nowrap;
  border-radius: 8px;
  cursor: pointer;
}

.iv__row:hover {
  text-decoration: underline;
  text-decoration-thickness: 3px;
  text-underline-offset: 4px;
}

.iv__row:focus-visible {
  outline: 3px solid #2f6df6;
  outline-offset: 2px;
}

.iv__preview {
  position: absolute;
  left: 0;
  top: 0;
  width: 150px;
  height: 110px;
  border: 3px solid #17141a;
  border-radius: 8px;
  background: #ffffff;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  will-change: transform;
}

.iv__art {
  position: absolute;
  inset: 0;
  border-radius: 4px;
  transition: opacity 220ms ease-out;
}

.iv__art--night {
  background: radial-gradient(circle at 78% 24%, rgba(255, 210, 63, 0.95) 0 7%, rgba(255, 210, 63, 0) 9%), radial-gradient(circle at 22% 70%, rgba(255, 210, 63, 0.8) 0 4%, rgba(255, 210, 63, 0) 6%), linear-gradient(180deg, #0a4fe8 0%, #17141a 100%);
}

.iv__art--sea {
  background: radial-gradient(circle at 72% 20%, rgba(255, 255, 255, 0.9) 0 9%, rgba(255, 255, 255, 0) 14%), linear-gradient(180deg, #6ec8ff 0%, #6ec8ff 52%, #4cd4a6 52%, #4cd4a6 100%);
}

.iv__art--forest {
  background: radial-gradient(circle at 26% 26%, rgba(255, 210, 63, 0.95) 0 10%, rgba(255, 210, 63, 0) 16%), linear-gradient(180deg, #4cd4a6 0%, #2b9d74 130%);
}

.iv__art--forest::before {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 46%;
  background: linear-gradient(135deg, transparent 0 18%, rgba(23, 20, 26, 0.8) 18% 32%, transparent 32% 48%, rgba(23, 20, 26, 0.8) 48% 66%, transparent 66%);
}

.iv__ribbon {
  position: absolute;
  left: -3px;
  top: 8px;
  padding: 4px 8px;
  background: #0a4fe8;
  color: #fff7e6;
  font-weight: 700;
  font-size: clamp(9px, 2.4vw, 10px);
  line-height: 1.3;
  border-radius: 0 4px 4px 0;
}

.iv__hint {
  margin: 0;
  color: #17141a;
  font-weight: 700;
  font-size: clamp(9px, 2.4vw, 11px);
}

.iv.is-demo .iv__preview {
  animation: ivTour 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes ivTour {
  0%, 8% {
    transform: translate3d(196px, 18px, 0) rotate(-3deg);
  }
  30%, 38% {
    transform: translate3d(232px, 48px, 0) rotate(3deg);
  }
  58%, 66% {
    transform: translate3d(210px, 78px, 0) rotate(-2deg);
  }
  88%, 100% {
    transform: translate3d(196px, 18px, 0) rotate(-3deg);
  }
}
@media (max-width: 340px) {
  .iv {
    gap: 8px;
  }
  .iv__scene {
    height: clamp(96px, 28vh, 130px);
  }
  .iv__preview {
    width: 120px;
    height: 88px;
  }
  .iv__list {
    padding: 0 8px;
  }
  .iv.is-demo .iv__preview {
    animation-name: ivTourNarrow;
  }
}
@keyframes ivTourNarrow {
  0%, 8% {
    transform: translate3d(148px, 14px, 0) rotate(-3deg);
  }
  30%, 38% {
    transform: translate3d(168px, 38px, 0) rotate(3deg);
  }
  58%, 66% {
    transform: translate3d(152px, 62px, 0) rotate(-2deg);
  }
  88%, 100% {
    transform: translate3d(148px, 14px, 0) rotate(-3deg);
  }
}
@media (prefers-reduced-motion: reduce) {
  .iv.is-demo .iv__preview {
    animation: none !important;
  }
  .iv.is-demo .iv__preview {
    transform: translate3d(196px, 40px, 0) rotate(0deg) !important;
  }
  .iv__art {
    transition: none;
  }
}

var root = document.getElementById('iv');
var preview = document.getElementById('ivPreview');
var ribbon = document.getElementById('ivRibbon');
var rows = Array.prototype.slice.call(document.querySelectorAll('.iv__row'));
var arts = { night: 0, sea: 1, forest: 2 };

var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

function lerp(a, b, k) { return a + (b - a) * k; }

var t = { x: 0, y: 0 };
var p = { x: 0, y: 0 };
var rot = 0;
var rotNow = 0;
var lastX = null;

function sceneRect() { return root.querySelector('.iv__scene').getBoundingClientRect(); }

function show(idx, label) {
  var cards = preview.querySelectorAll('.iv__art');
  for (var i = 0; i < cards.length; i++) {
    // 보여줄 장면만 opacity 1 — 나머지는 공간을 유지한 채 감춘다
    cards[i].style.opacity = i === idx ? '1' : '0';
  }
  ribbon.textContent = label;
}

function place(cx, cy) {
  var r = sceneRect();
  t.x = Math.min(r.width - 90, Math.max(90, cx - r.left));
  t.y = Math.min(r.height - 60, Math.max(60, cy - r.top));
  if (lastX !== null) {
    rot = Math.max(-7, Math.min(7, (cx - lastX) * 0.35));
  }
  lastX = cx;
}

function draw() {
  preview.style.transform = 'translate3d(' + (p.x - 75).toFixed(1) + 'px,' + (p.y - 55).toFixed(1) + 'px,0) rotate(' + rotNow.toFixed(1) + 'deg)';
}

function tick() {
  p.x = lerp(p.x, t.x, 0.13);
  p.y = lerp(p.y, t.y, 0.13);
  rotNow = lerp(rotNow, rot, 0.1);
  rot = lerp(rot, 0, 0.06);
  draw();
  requestAnimationFrame(tick);
}

function home() {
  var r = sceneRect();
  t = { x: r.width - 100, y: r.height * 0.62 };
  p = { x: t.x, y: t.y };
  rot = 0; rotNow = 0;
}

rows.forEach(function (row) {
  row.addEventListener('pointerenter', function (e) {
    root.classList.remove('is-demo');
    show(arts[row.dataset.scene], row.textContent);
    place(e.clientX, e.clientY);
  });
  row.addEventListener('focus', function () {
    root.classList.remove('is-demo');
    show(arts[row.dataset.scene], row.textContent);
  });
});

root.addEventListener('pointermove', function (e) {
  root.classList.remove('is-demo');
  place(e.clientX, e.clientY);
});

home();
show(0, rows[0].textContent);
draw();
if (reduce) {
  // reduce 에서는 그림이 줄 옆 고정 자리에 붙어 돌아다니지 않는다
  window.addEventListener('pointermove', function (e) {
    place(e.clientX, e.clientY);
    var r = sceneRect();
    p = { x: r.width - 100, y: r.height * 0.62 };
    rotNow = 0;
    draw();
  });
} else {
  requestAnimationFrame(tick);
}

// ImagePreview — vanilla 판(run/079/demo/08-follow-image-preview/index.html) 의 React 포트.
// 줄에 올리면 그 항목의 그림(그라디언트 장면)이 커서를 lerp(0.13)로 쫓아 떠오르고,
// 이동 방향에 따라 rotate 로 살짝 기울며 리본 이름표가 붙어 따라온다.
// 장면 전환은 vanilla 처럼 opacity 로 갈아 끼운다. 값·수치는 vanilla 와 같다.
import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./ImagePreview.module.scss";

export type ImagePreviewProps = {
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
// useRef 는 T | null 을 돌려준다. 처음부터 값이 있고 절대 비지 않는 상자는 이렇게 좁혀 쓴다
type Box<T> = { current: T };
// 전역 DOM 타입에 기대지 않는다 — 포인터 이벤트에서 실제로 읽는 것만 적는다
type PtrEvt = { clientX: number; clientY: number };

const SCENE_LABEL = "목록 세 줄 중 커서가 있는 줄의 그림이 커서를 쫓아 떠오르는 그림";
const HINT = "줄에 올리면 그 그림이 따라다닙니다";
// 줄 세 개 — 장면 키와 화면 문구. vanilla index.html 의 순서와 같다
const ROWS = [
  { key: "night", label: "밤하늘의 등불" },
  { key: "sea", label: "바다의 오후" },
  { key: "forest", label: "숲의 아침" },
];

// lerp: 매 프레임 남은 거리의 일부만 더 가는 선형 보간
function lerp(a: number, b: number, k: number): number {
  return a + (b - a) * k;
}

export default function ImagePreview({
  duration = 2000,
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#17141a",
}: ImagePreviewProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const sceneRef = useRef<HTMLDivElement | null>(null) as Box<HTMLDivElement>;
  const previewRef = useRef<HTMLDivElement | null>(null);
  const rowRef = useRef<(HTMLButtonElement | null)[]>(new Array(ROWS.length).fill(null)) as Box<(HTMLButtonElement | null)[]>;
  const [demo, setDemo] = useState(true);
  const [scene, setScene] = useState(0);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  function setRow(index: number) {
    return (el: HTMLButtonElement | null): void => {
      rowRef.current[index] = el;
    };
  }

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

    const t = { x: 0, y: 0 };
    const p = { x: 0, y: 0 };
    let rot = 0;
    let rotNow = 0;
    let lastX: number | null = null;

    function place(cx: number, cy: number): void {
      const r = sceneBox.getBoundingClientRect();
      t.x = Math.min(r.width - 90, Math.max(90, cx - r.left));
      t.y = Math.min(r.height - 60, Math.max(60, cy - r.top));
      if (lastX !== null) {
        rot = Math.max(-7, Math.min(7, (cx - lastX) * 0.35));
      }
      lastX = cx;
    }

    function draw(): void {
      const preview = previewRef.current;
      if (preview) {
        preview.style.transform =
          "translate3d(" + (p.x - 75).toFixed(1) + "px," + (p.y - 55).toFixed(1) + "px,0) rotate(" + rotNow.toFixed(1) + "deg)";
      }
    }

    function tick(): void {
      p.x = lerp(p.x, t.x, 0.13);
      p.y = lerp(p.y, t.y, 0.13);
      rotNow = lerp(rotNow, rot, 0.1);
      rot = lerp(rot, 0, 0.06);
      draw();
      raf = requestAnimationFrame(tick);
    }

    function home(): void {
      const r = sceneBox.getBoundingClientRect();
      t.x = r.width - 100;
      t.y = r.height * 0.62;
      p.x = t.x;
      p.y = t.y;
      rot = 0;
      rotNow = 0;
    }

    function onRowEnter(index: number, event: PtrEvt): void {
      setDemo(false);
      setScene(index);
      place(event.clientX, event.clientY);
    }
    function onRowFocus(index: number): void {
      setDemo(false);
      setScene(index);
    }
    function onMove(event: PtrEvt): void {
      setDemo(false);
      place(event.clientX, event.clientY);
    }
    // reduce 에서는 그림이 줄 옆 고정 자리에 붙어 돌아다니지 않는다
    function onReduceMove(event: PtrEvt): void {
      place(event.clientX, event.clientY);
      const r = sceneBox.getBoundingClientRect();
      p.x = r.width - 100;
      p.y = r.height * 0.62;
      rotNow = 0;
      draw();
    }

    const offs: (() => void)[] = [];
    rowRef.current.forEach((row, i) => {
      if (!row) return;
      const enter = (event: PtrEvt): void => onRowEnter(i, event);
      const focus = (): void => onRowFocus(i);
      row.addEventListener("pointerenter", enter);
      row.addEventListener("focus", focus);
      offs.push(() => {
        row.removeEventListener("pointerenter", enter);
        row.removeEventListener("focus", focus);
      });
    });
    root.addEventListener("pointermove", onMove);
    if (reduce) window.addEventListener("pointermove", onReduceMove);

    let raf = 0;
    home();
    setScene(0);
    draw();
    if (!reduce) raf = requestAnimationFrame(tick);
    return () => {
      offs.forEach((off) => off());
      root.removeEventListener("pointermove", onMove);
      if (reduce) window.removeEventListener("pointermove", onReduceMove);
      cancelAnimationFrame(raf);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.root + (demo ? " " + styles.isDemo : "")} style={vars} ref={rootRef}>
        <div className={styles.scene} ref={sceneRef} role="img" aria-label={SCENE_LABEL}>
          <ul className={styles.list}>
            {ROWS.map((row, i) => (
              <li key={row.key}>
                <button className={styles.row} type="button" ref={setRow(i)}>{row.label}</button>
              </li>
            ))}
          </ul>
          <div className={styles.preview} ref={previewRef} aria-hidden="true">
            <span className={styles.art + " " + styles.artNight} style={{ opacity: scene === 0 ? "1" : "0" }}></span>
            <span className={styles.art + " " + styles.artSea} style={{ opacity: scene === 1 ? "1" : "0" }}></span>
            <span className={styles.art + " " + styles.artForest} style={{ opacity: scene === 2 ? "1" : "0" }}></span>
            <span className={styles.ribbon}>{ROWS[scene].label}</span>
          </div>
        </div>
        <p className={styles.hint}>{HINT}</p>
      </div>
    </main>
  );
}