04固定画面のシーン切替

<main class="stage">
  <div class="ps">
    <div class="ps__scroll">
      <div class="ps__inner">
        <div class="ps__pin">
          <div class="ps__scene ps__scene--1"><span class="ps__cap">シーン 1 ・はじまり</span></div>
          <div class="ps__scene ps__scene--2 is-demo"><span class="ps__cap">シーン 2 ・慣れてきた頃</span></div>
          <div class="ps__scene ps__scene--3 is-demo"><span class="ps__cap">シーン 3 ・完成</span></div>
          <div class="ps__hint">上下にスクロール</div>
        </div>
      </div>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-orange);

.ps {
  width: min(400px, 88vw);
  height: clamp(150px, 62vh, 216px);
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

// 세로 스크롤 상자 자체가 타임라인 — 장면 셋이 이 한 줄을 공유한다
.ps__scroll {
  height: 100%;
  overflow-y: auto;
  scroll-timeline: --ps-scroll block;
  scrollbar-width: none;
  &::-webkit-scrollbar { display: none; }
}

.ps__inner { height: 300%; }

// ── 실제 동작: 화면(핀)은 고정, 스크롤 구간마다 장면이 서로 바뀐다 ──
.ps__pin {
  position: sticky;
  top: 0;
  height: calc(100% / 3);
  display: grid;
}

.ps__scene {
  grid-area: 1 / 1;
  display: grid;
  place-items: center;
}
.ps__scene--1 { background: linear-gradient(135deg, $subject-ink, #4a3f5c); }
.ps__scene--2 { background: linear-gradient(135deg, $color, #d6ddeb); }
.ps__scene--3 { background: linear-gradient(135deg, #c2ae82, $stage-yellow); }

.ps__cap {
  padding: $sp-1 $sp-4;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .4);
  color: $subject-cream;
  font: 700 13px/1.4 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.ps__hint {
  grid-area: 1 / 1;
  align-self: end;
  justify-self: center;
  margin-bottom: $sp-3;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .5);
  color: rgba(255, 255, 255, .92);
  font: 600 11px/1.4 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

@supports (animation-timeline: scroll()) {
  .ps__scene--1:not(.is-demo) { animation: ps-1 linear both; animation-timeline: --ps-scroll; }
  .ps__scene--2:not(.is-demo) { animation: ps-2 linear both; animation-timeline: --ps-scroll; }
  .ps__scene--3:not(.is-demo) { animation: ps-3 linear both; animation-timeline: --ps-scroll; }
}
@supports not (animation-timeline: scroll()) {
  // 미지원 브라우저(Firefox·Safari): 장면 1이 그대로 보인다
  .ps__scene--2:not(.is-demo), .ps__scene--3:not(.is-demo) { opacity: 0; }
}
// 전체 스크롤을 100% 로 보고 장면마다 제 구간을 차지한다
@keyframes ps-1 { 0% { opacity: 1; } 33%, 100% { opacity: 0; } }
@keyframes ps-2 { 0%, 30% { opacity: 0; } 38% { opacity: 1; } 62% { opacity: 1; } 70%, 100% { opacity: 0; } }
@keyframes ps-3 { 0%, 64% { opacity: 0; } 74%, 100% { opacity: 1; } }

// 데모 루프: 실제 스크롤 대신 장면이 순서대로 바뀌는 걸 흉내(캡처용)
.ps__scene--2.is-demo { animation: ps-loop-2 $duration linear infinite; }
.ps__scene--3.is-demo { animation: ps-loop-3 $duration linear infinite; }
@keyframes ps-loop-2 {
  0%, 14%   { opacity: 0; }
  26%, 46%  { opacity: 1; }
  58%, 100% { opacity: 0; }
}
@keyframes ps-loop-3 {
  0%, 58%   { opacity: 0; }
  70%, 92%  { opacity: 1; }
  100%      { opacity: 0; }
}

@media (prefers-reduced-motion: reduce) {
  .ps__scene.is-demo { animation: none !important; }
  .ps__scene--2.is-demo, .ps__scene--3.is-demo { opacity: 0 !important; }
  .ps__scroll { scroll-behavior: auto; }
}

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);
}

.ps {
  width: min(400px, 88vw);
  height: clamp(150px, 62vh, 216px);
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.ps__scroll {
  height: 100%;
  overflow-y: auto;
  scroll-timeline: --ps-scroll block;
  scrollbar-width: none;
}
.ps__scroll::-webkit-scrollbar {
  display: none;
}

.ps__inner {
  height: 300%;
}

.ps__pin {
  position: sticky;
  top: 0;
  height: 33.3333333333%;
  display: grid;
}

.ps__scene {
  grid-area: 1/1;
  display: grid;
  place-items: center;
}

.ps__scene--1 {
  background: linear-gradient(135deg, #17141a, #4a3f5c);
}

.ps__scene--2 {
  background: linear-gradient(135deg, #2f6df6, #d6ddeb);
}

.ps__scene--3 {
  background: linear-gradient(135deg, #c2ae82, #ffd23f);
}

.ps__cap {
  padding: 4px 16px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.4);
  color: #fff7e6;
  font: 700 13px/1.4 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.ps__hint {
  grid-area: 1/1;
  align-self: end;
  justify-self: center;
  margin-bottom: 12px;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.5);
  color: rgba(255, 255, 255, 0.92);
  font: 600 11px/1.4 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

@supports (animation-timeline: scroll()) {
  .ps__scene--1:not(.is-demo) {
    animation: ps-1 linear both;
    animation-timeline: --ps-scroll;
  }
  .ps__scene--2:not(.is-demo) {
    animation: ps-2 linear both;
    animation-timeline: --ps-scroll;
  }
  .ps__scene--3:not(.is-demo) {
    animation: ps-3 linear both;
    animation-timeline: --ps-scroll;
  }
}
@supports not (animation-timeline: scroll()) {
  .ps__scene--2:not(.is-demo), .ps__scene--3:not(.is-demo) {
    opacity: 0;
  }
}
@keyframes ps-1 {
  0% {
    opacity: 1;
  }
  33%, 100% {
    opacity: 0;
  }
}
@keyframes ps-2 {
  0%, 30% {
    opacity: 0;
  }
  38% {
    opacity: 1;
  }
  62% {
    opacity: 1;
  }
  70%, 100% {
    opacity: 0;
  }
}
@keyframes ps-3 {
  0%, 64% {
    opacity: 0;
  }
  74%, 100% {
    opacity: 1;
  }
}
.ps__scene--2.is-demo {
  animation: ps-loop-2 2s linear infinite;
}

.ps__scene--3.is-demo {
  animation: ps-loop-3 2s linear infinite;
}

@keyframes ps-loop-2 {
  0%, 14% {
    opacity: 0;
  }
  26%, 46% {
    opacity: 1;
  }
  58%, 100% {
    opacity: 0;
  }
}
@keyframes ps-loop-3 {
  0%, 58% {
    opacity: 0;
  }
  70%, 92% {
    opacity: 1;
  }
  100% {
    opacity: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ps__scene.is-demo {
    animation: none !important;
  }
  .ps__scene--2.is-demo, .ps__scene--3.is-demo {
    opacity: 0 !important;
  }
  .ps__scroll {
    scroll-behavior: auto;
  }
}

// 실제 동작은 scroll-timeline + animation-timeline(장면마다 키프레임 구간)만으로 끝난다(0줄).
// 장면 2·3의 is-demo 클래스는 캡처용 미리보기 루프일 뿐 — 실제 스크롤 반응은 그대로 살아있다.

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

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

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

export default function SceneSwap({ duration = 300, easing = "linear", color = "#2f6df6" }: SceneSwapProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <div className={styles.ps} style={vars}>
      {/* 스크롤 상자 자체가 타임라인 — 장면 셋이 이 한 줄을 공유하고 키프레임 구간으로 나눠 갖는다 */}
      <div className={styles.scroll}>
        <div className={styles.inner}>
          <div className={styles.pin}>
            <div className={`${styles.scene} ${styles.scene1}`}>장면 1 · 처음</div>
            <div className={`${styles.scene} ${styles.scene2}`}>장면 2 · 익숙해질 때</div>
            <div className={`${styles.scene} ${styles.scene3}`}>장면 3 · 완성</div>
            <div className={styles.hint}>위아래로 스크롤</div>
          </div>
        </div>
      </div>
    </div>
  );
}