07Panorama that splits front to back

<main class="stage">
<div class="tp is-demo" id="tp">
  <div class="tp__window" id="window" role="img" aria-label="A view where sky, hills, and field each travel a different distance with the pointer">
    <span class="tp__layer tp__layer--sky" aria-hidden="true"><span class="tp__sun"></span></span>
    <span class="tp__layer tp__layer--hill" aria-hidden="true"><i class="tp__peak tp__peak--l"></i><i class="tp__peak tp__peak--r"></i></span>
    <span class="tp__layer tp__layer--field" aria-hidden="true"></span>
    <span class="tp__caption">South Jeju hills</span>
  </div>
  <p class="tp__hint">Move the pointer sideways and the layers pull apart</p>
</div>
</main>

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

// 앞뒤로 갈라지는 풍경 파노라마 — 겹마다 다른 이동 계수(--depth)를 두고 JS 는 포인터 x 를 -1~1 로 바꿔 --px 하나만 넘긴다.
// 배경(하늘)은 8px, 중경(산)은 22px, 전경(들판)은 44px 움직인다 — 가까울수록 많이 움직이는 것이 깊이로 읽힌다.
// 격자 미리보기(.is-demo)는 그 세 폭을 @keyframes 로 왕복시킨다.

$duration: $dur-loop;
$easing: linear;
$color: $subject-ink;

@include stage($stage-yellow);

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

.tp__window {
  --px: 0;
  position: relative; overflow: hidden;
  width: clamp(232px, 60vw, 296px); height: clamp(104px, 28vw, 136px);
  border-radius: $r-card;
  border: 3px solid $color;
  background: $subject-blue;
}
.tp__window:focus-visible { outline: 3px solid $color; outline-offset: $sp-2; }

.tp__layer {
  position: absolute; left: -12%; right: -12%;
  transform: translateX(calc(var(--px) * var(--depth)));
}
.tp__layer--sky {
  --depth: 8px;
  top: 0; height: 62%;
  background: linear-gradient(180deg, $subject-blue 0%, rgba($subject-cream, .5) 100%);
}
.tp__sun {
  position: absolute; left: 62%; top: 22%;
  width: 26px; height: 26px;
  border-radius: 50%;
  background: $stage-yellow;
  box-shadow: 0 0 20px rgba(255, 210, 63, .9);
}
// 산은 clip-path 삼각형 두 개 — 그라디언트로 그리면 반쪽 쐐기가 되어 능선으로 안 읽힌다
.tp__layer--hill {
  --depth: 22px;
  bottom: 26%; height: 48%;
}
.tp__peak {
  position: absolute; bottom: 0; height: 100%;
  clip-path: polygon(50% 0, 100% 100%, 0 100%);
}
.tp__peak--l { left: 14%; width: 34%; background: rgba($subject-ink, .78); }
.tp__peak--r { left: 46%; width: 44%; height: 82%; background: $subject-ink; }

.tp__layer--field {
  --depth: 44px;
  bottom: 0; height: 30%;
  background: repeating-linear-gradient(96deg, $subject-ink 0 14px, rgba($subject-ink, .82) 14px 28px);
  border-top: 3px solid $color;
}
.tp__caption {
  position: absolute; left: $sp-3; top: $sp-2;
  padding: $sp-1 $sp-2;
  border-radius: $r-pill;
  background: rgba($subject-cream, .92); color: $color;
  font-weight: 800; font-size: clamp(9px, 2.4vw, 11px);
}
.tp__hint { margin: 0; color: $color; font-weight: 700; font-size: clamp(9px, 2.4vw, 11px); }

// ── 미리보기 루프: --px 가 -1 → 1 로 지나간 것과 같은 결과를 겹마다 직접 그린다
.tp.is-demo .tp__layer {
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.tp.is-demo .tp__layer--sky   { animation-name: tpSky; }
.tp.is-demo .tp__layer--hill  { animation-name: tpHill; }
.tp.is-demo .tp__layer--field { animation-name: tpField; }

@keyframes tpSky {
  0%, 6%    { transform: translateX(-8px); }
  46%, 58%  { transform: translateX(8px); }
  94%, 100% { transform: translateX(-8px); }
}
@keyframes tpHill {
  0%, 6%    { transform: translateX(-22px); }
  46%, 58%  { transform: translateX(22px); }
  94%, 100% { transform: translateX(-22px); }
}
@keyframes tpField {
  0%, 6%    { transform: translateX(-44px); }
  46%, 58%  { transform: translateX(44px); }
  94%, 100% { transform: translateX(-44px); }
}

@media (max-width: 340px) {
  .tp__caption { left: $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .tp.is-demo .tp__layer { animation: none !important; }
  // 움직임 없이 겹이 갈라진 자리로 세운다
  .tp.is-demo .tp__layer--sky   { transform: translateX(4px) !important; }
  .tp.is-demo .tp__layer--hill  { transform: translateX(12px) !important; }
  .tp.is-demo .tp__layer--field { transform: translateX(24px) !important; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

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

.tp__window {
  --px: 0;
  position: relative;
  overflow: hidden;
  width: clamp(232px, 60vw, 296px);
  height: clamp(104px, 28vw, 136px);
  border-radius: 16px;
  border: 3px solid #17141a;
  background: #2f6df6;
}

.tp__window:focus-visible {
  outline: 3px solid #17141a;
  outline-offset: 8px;
}

.tp__layer {
  position: absolute;
  left: -12%;
  right: -12%;
  transform: translateX(calc(var(--px) * var(--depth)));
}

.tp__layer--sky {
  --depth: 8px;
  top: 0;
  height: 62%;
  background: linear-gradient(180deg, #2f6df6 0%, rgba(255, 247, 230, 0.5) 100%);
}

.tp__sun {
  position: absolute;
  left: 62%;
  top: 22%;
  width: 26px;
  height: 26px;
  border-radius: 50%;
  background: #ffd23f;
  box-shadow: 0 0 20px rgba(255, 210, 63, 0.9);
}

.tp__layer--hill {
  --depth: 22px;
  bottom: 26%;
  height: 48%;
}

.tp__peak {
  position: absolute;
  bottom: 0;
  height: 100%;
  clip-path: polygon(50% 0, 100% 100%, 0 100%);
}

.tp__peak--l {
  left: 14%;
  width: 34%;
  background: rgba(23, 20, 26, 0.78);
}

.tp__peak--r {
  left: 46%;
  width: 44%;
  height: 82%;
  background: #17141a;
}

.tp__layer--field {
  --depth: 44px;
  bottom: 0;
  height: 30%;
  background: repeating-linear-gradient(96deg, #17141a 0 14px, rgba(23, 20, 26, 0.82) 14px 28px);
  border-top: 3px solid #17141a;
}

.tp__caption {
  position: absolute;
  left: 12px;
  top: 8px;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.92);
  color: #17141a;
  font-weight: 800;
  font-size: clamp(9px, 2.4vw, 11px);
}

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

.tp.is-demo .tp__layer {
  animation-duration: 2s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
}

.tp.is-demo .tp__layer--sky {
  animation-name: tpSky;
}

.tp.is-demo .tp__layer--hill {
  animation-name: tpHill;
}

.tp.is-demo .tp__layer--field {
  animation-name: tpField;
}

@keyframes tpSky {
  0%, 6% {
    transform: translateX(-8px);
  }
  46%, 58% {
    transform: translateX(8px);
  }
  94%, 100% {
    transform: translateX(-8px);
  }
}
@keyframes tpHill {
  0%, 6% {
    transform: translateX(-22px);
  }
  46%, 58% {
    transform: translateX(22px);
  }
  94%, 100% {
    transform: translateX(-22px);
  }
}
@keyframes tpField {
  0%, 6% {
    transform: translateX(-44px);
  }
  46%, 58% {
    transform: translateX(44px);
  }
  94%, 100% {
    transform: translateX(-44px);
  }
}
@media (max-width: 340px) {
  .tp__caption {
    left: 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .tp.is-demo .tp__layer {
    animation: none !important;
  }
  .tp.is-demo .tp__layer--sky {
    transform: translateX(4px) !important;
  }
  .tp.is-demo .tp__layer--hill {
    transform: translateX(12px) !important;
  }
  .tp.is-demo .tp__layer--field {
    transform: translateX(24px) !important;
  }
}

var tp = document.getElementById('tp');
var frame = document.getElementById('window');
var aim = 0, now = 0, running = false;

// 겹마다 다른 계수는 CSS 가 --depth 로 갖고 있고, JS 는 -1~1 한 값(--px)만 넘긴다
function step() {
  now += (aim - now) * 0.12;
  frame.style.setProperty('--px', now.toFixed(3));
  if (Math.abs(aim - now) < 0.002) { frame.style.setProperty('--px', aim.toFixed(3)); running = false; return; }
  requestAnimationFrame(step);
}

function start() { if (!running) { running = true; requestAnimationFrame(step); } }

frame.addEventListener('pointermove', function (e) {
  tp.classList.remove('is-demo');
  var r = frame.getBoundingClientRect();
  aim = Math.max(-1, Math.min(1, (e.clientX - r.left) / r.width * 2 - 1));
  start();
});
frame.addEventListener('pointerleave', function () { aim = 0; start(); });
// 키보드 경로: 좌우 화살표로 같은 범위를 0.25씩 움직인다
frame.setAttribute('tabindex', '0');
frame.addEventListener('keydown', function (e) {
  var move = e.key === 'ArrowLeft' ? -0.25 : e.key === 'ArrowRight' ? 0.25 : 0;
  if (!move) { return; }
  e.preventDefault();
  tp.classList.remove('is-demo');
  aim = Math.max(-1, Math.min(1, aim + move));
  start();
});

// TerrainPanorama — vanilla 판(run/290/demo/07-pointer-3d-terrain-panorama/index.html) 의 React 포트.
// 겹마다 다른 이동 계수(--depth)는 CSS 가 갖고 있고, 여기서는 포인터 x 를 -1~1 로 바꾼 값(--px) 하나만 넘긴다.
// 그 한 값이 requestAnimationFrame 루프에서 0.12 씩 목표로 다가가므로 겹이 관성 있게 따라온다.
// 값·수치는 vanilla 와 같다.
import { useEffect, useRef, useState } from "react";
import type { CSSProperties, PointerEvent as ReactPointerEvent } from "react";
import styles from "./TerrainPanorama.module.scss";

export type TerrainPanoramaProps = {
  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 — 키보드 이벤트에서 실제로 쓰는 두 가지만 적는다
type KeyEvt = { key: string; preventDefault(): void };

const WINDOW_LABEL = "하늘, 산, 들판 세 겹이 마우스를 따라 서로 다른 거리로 움직이는 풍경";
const CAPTION = "제주 남쪽 오름";
const HINT = "마우스를 좌우로 옮기면 겹이 갈라집니다";

function clampAim(value: number): number {
  return Math.max(-1, Math.min(1, value));
}

export default function TerrainPanorama({
  duration = 2000,
  easing = "linear",
  color = "#17141a",
}: TerrainPanoramaProps) {
  const frameRef = useRef<HTMLDivElement | null>(null);
  const aimRef = useRef<number>(0) as Box<number>;
  const nowRef = useRef<number>(0) as Box<number>;
  const runningRef = useRef<boolean>(false) as Box<boolean>;
  const rafRef = useRef<number>(0) as Box<number>;
  const [demo, setDemo] = useState(true);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  // 함수 선언이라 자기 이름을 안전하게 다시 부른다 — 프레임마다 목표까지 남은 거리의 12% 를 좁힌다
  function step(): void {
    const frame = frameRef.current;
    if (!frame) {
      runningRef.current = false;
      return;
    }
    nowRef.current += (aimRef.current - nowRef.current) * 0.12;
    frame.style.setProperty("--px", nowRef.current.toFixed(3));
    if (Math.abs(aimRef.current - nowRef.current) < 0.002) {
      frame.style.setProperty("--px", aimRef.current.toFixed(3));
      runningRef.current = false;
      return;
    }
    rafRef.current = requestAnimationFrame(step);
  }

  function start(): void {
    if (!runningRef.current) {
      runningRef.current = true;
      rafRef.current = requestAnimationFrame(step);
    }
  }

  useEffect(() => {
    return () => {
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  function onPointerMove(event: ReactPointerEvent<HTMLDivElement>): void {
    const frame = frameRef.current;
    if (!frame) return;
    setDemo(false);
    const r = frame.getBoundingClientRect();
    aimRef.current = clampAim(((event.clientX - r.left) / r.width) * 2 - 1);
    start();
  }

  function onPointerLeave(): void {
    aimRef.current = 0;
    start();
  }

  // 키보드 경로: 좌우 화살표로 같은 범위를 0.25씩 움직인다
  function onKeyDown(event: KeyEvt): void {
    const move = event.key === "ArrowLeft" ? -0.25 : event.key === "ArrowRight" ? 0.25 : 0;
    if (!move) return;
    event.preventDefault();
    setDemo(false);
    aimRef.current = clampAim(aimRef.current + move);
    start();
  }

  const cls = [styles.root, demo ? styles.isDemo : ""].filter(Boolean).join(" ");
  return (
    <main className={styles.stage}>
      <div className={cls} style={vars}>
        <div
          className={styles.window}
          ref={frameRef}
          role="img"
          aria-label={WINDOW_LABEL}
          tabIndex={0}
          onPointerMove={onPointerMove}
          onPointerLeave={onPointerLeave}
          onKeyDown={onKeyDown}
        >
          <span className={`${styles.layer} ${styles.layerSky}`} aria-hidden="true">
            <span className={styles.sun}></span>
          </span>
          <span className={`${styles.layer} ${styles.layerHill}`} aria-hidden="true">
            <i className={`${styles.peak} ${styles.peakL}`}></i>
            <i className={`${styles.peak} ${styles.peakR}`}></i>
          </span>
          <span className={`${styles.layer} ${styles.layerField}`} aria-hidden="true"></span>
          <span className={styles.caption}>{CAPTION}</span>
        </div>
        <p className={styles.hint}>{HINT}</p>
      </div>
    </main>
  );
}