08Two-image cross-fade

<main class="stage">
  <figure class="photo is-demo" tabindex="0">
    <span class="photo__frame" aria-hidden="true">
      <span class="photo__a">
        <span class="photo__sun"></span>
        <span class="photo__hill"></span>
      </span>
      <span class="photo__b">
        <span class="photo__sun photo__sun--b"></span>
        <span class="photo__hill photo__hill--b"></span>
      </span>
    </span>
    <figcaption class="photo__cap">Color options</figcaption>
  </figure>
</main>

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

$duration: $dur-base;                               // 두 번째 사진이 번지는 시간
$easing: $ease-out;
$color: $subject-ink;                                // 사진 프레임 색

@include stage($stage-paper);
.stage { padding: clamp(6px, 2.4vw, 16px); }   // 320px 대응: 데모 카드가 작아 여백도 줄인다

.photo {
  margin: 0;
  width: min(160px, 50vw);
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  border: 3px solid $color;
  outline: none;
  cursor: pointer;
}
.photo__frame {
  display: block;
  position: relative;
  aspect-ratio: 4 / 3;
}
.photo__a,
.photo__b {
  position: absolute;
  inset: 0;
}
.photo__a {
  background: linear-gradient(155deg, $subject-cream 0%, $subject-blue 100%);
}
.photo__b {
  background: linear-gradient(155deg, $subject-blue 0%, $subject-ink 100%);
  opacity: 0;                                         // 평소엔 첫 사진만 보인다
  transition: opacity $duration $easing;
}
.photo__sun {
  position: absolute;
  top: 16%;
  right: 18%;
  width: 20%;
  aspect-ratio: 1;
  border-radius: 50%;
  background: $stage-yellow;
}
.photo__sun--b { background: $subject-cream; }
.photo__hill {
  position: absolute;
  left: -8%;
  right: -8%;
  bottom: -10%;
  height: 48%;
  border-radius: 50% 50% 0 0 / 100% 100% 0 0;
  background: $subject-ink;
  opacity: .85;
}
.photo__hill--b { background: $stage-orange; }
.photo__cap {
  word-break: keep-all;
  margin: 0;
  padding: 10px 14px;
  font-weight: 600; font-size: clamp(12px, 3.4vw, 14px); line-height: 1.3; font-family: inherit;
  color: $subject-cream;
  background: $color;
}

.photo:hover .photo__b,
.photo:focus-visible .photo__b,
.photo:active .photo__b {
  opacity: 1;
}

.photo.is-demo .photo__b {
  animation: cross-loop $dur-loop $easing infinite;
}

@keyframes cross-loop {
  0%, 20%  { opacity: 0; }
  50%, 75% { opacity: 1; }
  100%     { opacity: 0; }
}

@media (hover: none) {
  .photo:active .photo__b { opacity: 1; }
}

@media (prefers-reduced-motion: reduce) {
  .photo__b { transition: none; }
  .photo.is-demo .photo__b { animation: 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);
}

.stage {
  padding: clamp(6px, 2.4vw, 16px);
}

.photo {
  margin: 0;
  width: min(160px, 50vw);
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  border: 3px solid #17141a;
  outline: none;
  cursor: pointer;
}

.photo__frame {
  display: block;
  position: relative;
  aspect-ratio: 4/3;
}

.photo__a,
.photo__b {
  position: absolute;
  inset: 0;
}

.photo__a {
  background: linear-gradient(155deg, #fff7e6 0%, #2f6df6 100%);
}

.photo__b {
  background: linear-gradient(155deg, #2f6df6 0%, #17141a 100%);
  opacity: 0;
  transition: opacity 300ms ease-out;
}

.photo__sun {
  position: absolute;
  top: 16%;
  right: 18%;
  width: 20%;
  aspect-ratio: 1;
  border-radius: 50%;
  background: #ffd23f;
}

.photo__sun--b {
  background: #fff7e6;
}

.photo__hill {
  position: absolute;
  left: -8%;
  right: -8%;
  bottom: -10%;
  height: 48%;
  border-radius: 50% 50% 0 0/100% 100% 0 0;
  background: #17141a;
  opacity: 0.85;
}

.photo__hill--b {
  background: #ff4d1f;
}

.photo__cap {
  word-break: keep-all;
  margin: 0;
  padding: 10px 14px;
  font-weight: 600;
  font-size: clamp(12px, 3.4vw, 14px);
  line-height: 1.3;
  font-family: inherit;
  color: #fff7e6;
  background: #17141a;
}

.photo:hover .photo__b,
.photo:focus-visible .photo__b,
.photo:active .photo__b {
  opacity: 1;
}

.photo.is-demo .photo__b {
  animation: cross-loop 2s ease-out infinite;
}

@keyframes cross-loop {
  0%, 20% {
    opacity: 0;
  }
  50%, 75% {
    opacity: 1;
  }
  100% {
    opacity: 0;
  }
}
@media (hover: none) {
  .photo:active .photo__b {
    opacity: 1;
  }
}
@media (prefers-reduced-motion: reduce) {
  .photo__b {
    transition: none;
  }
  .photo.is-demo .photo__b {
    animation: none;
  }
}

import type { CSSProperties } from "react";
import styles from "./CrossFadePhoto.module.scss";

export type CrossFadePhotoProps = {
  caption: string;
  /** 두 번째 사진이 번지는 시간 (기본 300ms) */
  duration?: number;
  easing?: string;
  /** 프레임 색 */
  color?: string;
};

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

export default function CrossFadePhoto({
  caption,
  duration = 300,
  easing = "ease-out",
  color = "#17141a",
}: CrossFadePhotoProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <figure className={styles.photo} style={vars} tabIndex={0}>
      <span className={styles.frame} aria-hidden="true">
        <span className={styles.a}>
          <span className={styles.sun} />
          <span className={styles.hill} />
        </span>
        <span className={styles.b}>
          <span className={`${styles.sun} ${styles.sunB}`} />
          <span className={`${styles.hill} ${styles.hillB}`} />
        </span>
      </span>
      <figcaption className={styles.cap}>{caption}</figcaption>
    </figure>
  );
}