09ルート遷移アニメーション

<main class="stage">
  <div class="rt-frame is-demo">
    <div class="rt-page rt-page--out">
      <span class="rt-page__label">/ home</span>
    </div>
    <div class="rt-page rt-page--in">
      <span class="rt-page__label">/ pricing</span>
    </div>
  </div>
</main>

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

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

@include stage($stage-ink);

.rt-frame {
  position: relative;
  width: min(280px, 88vw);
  aspect-ratio: 280 / 160;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.rt-page {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
}

.rt-page--out { background: linear-gradient(160deg, rgba(255, 255, 255, .12), rgba(255, 255, 255, .02)); }
.rt-page--in  { background: linear-gradient(160deg, $color, rgba(23, 20, 26, .9)); }

.rt-page__label {
  padding: $sp-2 $sp-5;
  border-radius: $r-pill;
  background: rgba(0, 0, 0, .28);
  color: $subject-cream;
  font: 700 13px/1 "SFMono-Regular", Consolas, monospace;
}

// 실사용 원리: URL 파라미터를 컴포넌트의 key 로 쓰거나 라우트 전환을 startViewTransition 으로
// 감싸면, 나가는 페이지와 들어오는 페이지가 순간 전환 대신 CSS 트랜지션으로 이어진다.
.rt-page--in { transform: translateX(100%); }

// 캡처용 루프: home 이 왼쪽으로 나가고 pricing 이 오른쪽에서 들어오는 전환을 2초 주기로 반복
@keyframes rt-out { 0%, 15% { transform: none; } 75%, 100% { transform: translateX(-100%); } }
@keyframes rt-in  { 0%, 15% { transform: translateX(100%); } 75%, 100% { transform: none; } }
.rt-frame.is-demo .rt-page--out { animation: rt-out $dur-loop $easing infinite; }
.rt-frame.is-demo .rt-page--in  { animation: rt-in $dur-loop $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .rt-frame.is-demo .rt-page--out,
  .rt-frame.is-demo .rt-page--in { animation: none !important; }
  .rt-page--out { transform: none; }
  .rt-page--in { transform: translateX(100%); }
}

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);
}

.rt-frame {
  position: relative;
  width: min(280px, 88vw);
  aspect-ratio: 280/160;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.rt-page {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
}

.rt-page--out {
  background: linear-gradient(160deg, rgba(255, 255, 255, 0.12), rgba(255, 255, 255, 0.02));
}

.rt-page--in {
  background: linear-gradient(160deg, #2f6df6, rgba(23, 20, 26, 0.9));
}

.rt-page__label {
  padding: 8px 20px;
  border-radius: 999px;
  background: rgba(0, 0, 0, 0.28);
  color: #fff7e6;
  font: 700 13px/1 "SFMono-Regular", Consolas, monospace;
}

.rt-page--in {
  transform: translateX(100%);
}

@keyframes rt-out {
  0%, 15% {
    transform: none;
  }
  75%, 100% {
    transform: translateX(-100%);
  }
}
@keyframes rt-in {
  0%, 15% {
    transform: translateX(100%);
  }
  75%, 100% {
    transform: none;
  }
}
.rt-frame.is-demo .rt-page--out {
  animation: rt-out 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.rt-frame.is-demo .rt-page--in {
  animation: rt-in 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@media (prefers-reduced-motion: reduce) {
  .rt-frame.is-demo .rt-page--out,
  .rt-frame.is-demo .rt-page--in {
    animation: none !important;
  }
  .rt-page--out {
    transform: none;
  }
  .rt-page--in {
    transform: translateX(100%);
  }
}

import { CSSProperties, useState } from "react";
import styles from "./RouteTransition.module.scss";

const ROUTES = ["/ home", "/ pricing"];

function Page({ label }: { label: string; key?: string }) {
  // key={label} on the caller side makes each route its own component instance —
  // switching the key unmounts the outgoing page and mounts the incoming one,
  // instead of patching one page's content in place.
  return (
    <div className={styles.page}>
      <span className={styles.label}>{label}</span>
    </div>
  );
}

export interface RouteTransitionProps {
  duration?: string;
  easing?: string;
}

export default function RouteTransition({
  duration = "300ms",
  easing = "cubic-bezier(.2, .8, .2, 1)",
}: RouteTransitionProps) {
  const [route, setRoute] = useState(0);

  const navigate = () => {
    const next = (route + 1) % ROUTES.length;
    if (typeof document !== "undefined" && "startViewTransition" in document) {
      (document as any).startViewTransition(() => setRoute(next));
    } else {
      setRoute(next);
    }
  };

  const style: CSSProperties & { "--duration"?: string; "--easing"?: string } = {
    "--duration": duration,
    "--easing": easing,
  };

  return (
    <button className={styles.frame} style={style} onClick={navigate}>
      <Page key={ROUTES[route]} label={ROUTES[route]} />
    </button>
  );
}