03Shared element hero morph

<main class="stage">
  <div class="pages is-demo">
    <section class="page page--list">
      <p class="page__tag">GALLERY</p>
      <div class="thumb-row">
        <span class="thumb thumb--hero"></span>
        <span class="thumb"></span>
        <span class="thumb"></span>
      </div>
    </section>
    <div class="hero"></div>
    <p class="hero__caption">Photo detail</p>
  </div>
</main>

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

// ── 변수 3개. 변형은 이것만 바꾼다 (값은 토큰에서 받는다) ──────
$duration: $dur-enter;
$easing: $ease-spring;
$color: $subject-cream;

// ── 데모 무대 ───────────────────────────────
@include stage($stage-orange);

.pages { position: relative; width: min(300px, 88%); height: 150px; border-radius: $r-card; overflow: hidden; box-shadow: $shadow-raised; background: #fff; }
.page--list { position: absolute; inset: 0; box-sizing: border-box; padding: clamp(12px, 5vw, 18px); display: flex; flex-direction: column; gap: 10px; }
.page__tag { margin: 0; font-weight: 700; font-size: clamp(9px, 2.6vw, 11px); line-height: 1; font-family: inherit; letter-spacing: .12em; color: $subject-ink; opacity: .55; }
.thumb-row { display: flex; gap: 8px; }
.thumb { flex: 1; height: 44px; border-radius: 8px; background: $subject-ink; opacity: .14; }
.thumb--hero { background: $subject-blue; opacity: 1; }

// 목록의 썸네일 하나(:first-child)가 그대로 늘어나며 히어로 이미지가 된다.
// transform-origin 을 썸네일 위치에 두고 scale·translate 만 바꾼다.
.hero {
  position: absolute; left: clamp(12px, 5vw, 18px); top: 46px; width: 30%; height: 44px;
  border-radius: 8px; background: $subject-blue;
  transform-origin: top left; // 규칙8: 공유요소 앵커, 실제론 w/h 애니메이션
  animation: hero-grow $dur-loop $easing infinite;
}
.hero__caption {
  position: absolute; left: clamp(12px, 5vw, 18px); bottom: 14px; margin: 0;
  font-weight: 700; font-size: clamp(11px, 3.4vw, 13px); line-height: 1; font-family: inherit; color: $subject-ink;
  animation: caption-in $dur-loop $easing infinite;
}

@keyframes hero-grow {
  0%, 40% { transform: scale(1) translate(0, 0); width: 30%; height: 44px; }
  70%, 90% { transform: scale(1) translate(0, 0); width: 88%; height: 108px; top: 12px; }
  100% { transform: scale(1) translate(0, 0); width: 30%; height: 44px; top: 46px; }
}
@keyframes caption-in {
  0%, 55% { opacity: 0; }
  75%, 90% { opacity: 1; }
  100% { opacity: 0; }
}

// ── 접근성: 움직임 줄이기 설정이면 최종 상태만 고정으로 ────────
@media (prefers-reduced-motion: reduce) {
  .hero, .hero__caption { animation: none !important; }
  .hero__caption { opacity: 0; }
}

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);
}

.pages {
  position: relative;
  width: min(300px, 88%);
  height: 150px;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #fff;
}

.page--list {
  position: absolute;
  inset: 0;
  box-sizing: border-box;
  padding: clamp(12px, 5vw, 18px);
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.page__tag {
  margin: 0;
  font-weight: 700;
  font-size: clamp(9px, 2.6vw, 11px);
  line-height: 1;
  font-family: inherit;
  letter-spacing: 0.12em;
  color: #17141a;
  opacity: 0.55;
}

.thumb-row {
  display: flex;
  gap: 8px;
}

.thumb {
  flex: 1;
  height: 44px;
  border-radius: 8px;
  background: #17141a;
  opacity: 0.14;
}

.thumb--hero {
  background: #2f6df6;
  opacity: 1;
}

.hero {
  position: absolute;
  left: clamp(12px, 5vw, 18px);
  top: 46px;
  width: 30%;
  height: 44px;
  border-radius: 8px;
  background: #2f6df6;
  transform-origin: top left;
  animation: hero-grow 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.hero__caption {
  position: absolute;
  left: clamp(12px, 5vw, 18px);
  bottom: 14px;
  margin: 0;
  font-weight: 700;
  font-size: clamp(11px, 3.4vw, 13px);
  line-height: 1;
  font-family: inherit;
  color: #17141a;
  animation: caption-in 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes hero-grow {
  0%, 40% {
    transform: scale(1) translate(0, 0);
    width: 30%;
    height: 44px;
  }
  70%, 90% {
    transform: scale(1) translate(0, 0);
    width: 88%;
    height: 108px;
    top: 12px;
  }
  100% {
    transform: scale(1) translate(0, 0);
    width: 30%;
    height: 44px;
    top: 46px;
  }
}
@keyframes caption-in {
  0%, 55% {
    opacity: 0;
  }
  75%, 90% {
    opacity: 1;
  }
  100% {
    opacity: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .hero, .hero__caption {
    animation: none !important;
  }
  .hero__caption {
    opacity: 0;
  }
}

import type { CSSProperties, ReactNode } from "react";
import styles from "./SharedHeroTransition.module.scss";

export type SharedHeroTransitionProps = {
  /** "list": 썸네일 격자, "hero": 확대된 상세 */
  active: "list" | "hero";
  caption: ReactNode;
  /** 확대가 끝나는 시간 (기본 600ms) */
  duration?: number;
  easing?: string;
  color?: string;
  className?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

export default function SharedHeroTransition({
  active,
  caption,
  duration = 600,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
  className = "",
}: SharedHeroTransitionProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <div className={`${styles.pages} ${className}`} style={vars} data-active={active}>
      <div className={styles.thumbRow}>
        <span className={styles.thumb} />
        <span className={styles.thumb} />
      </div>
      <div className={styles.hero} />
      <p className={styles.caption}>{caption}</p>
    </div>
  );
}