08Three-layer parallax

<main class="stage">
  <section class="px is-demo" id="px" aria-label="Three-layer parallax demo">
    <header class="px__head">
      <p class="px__title">Three-layer parallax</p>
      <p class="px__attr"><code>lerp(cur, tgt, 0.12)</code></p>
    </header>
    <div class="px__view" id="px-view" tabindex="0" role="region" aria-label="Stars, hills and type — each layer travels its own distance as you scroll">
      <div class="px__scene">
        <div class="px__layer px__layer--stars" data-rate="0.12" aria-hidden="true"></div>
        <div class="px__layer px__layer--hills" data-rate="0.3" aria-hidden="true">
          <svg class="px__hills" viewBox="0 0 320 130" preserveAspectRatio="none">
            <path class="px__hill px__hill--back" d="M0 130 L0 72 C 34 30, 84 16, 128 46 C 168 74, 206 78, 244 62 C 276 48, 302 52, 320 60 L320 130 Z"></path>
            <path class="px__hill px__hill--front" d="M0 130 L0 100 C 50 62, 100 68, 148 88 C 198 110, 250 92, 320 70 L320 130 Z"></path>
          </svg>
        </div>
        <div class="px__layer px__layer--type" data-rate="0.55">
          <p class="px__word">SCROLL</p>
        </div>
      </div>
      <div class="px__spacer" aria-hidden="true"></div>
    </div>
    <footer class="px__foot">
      <span class="px__dot" aria-hidden="true"></span>
      <span class="px__state">Each layer rides its own ratio via <b>translate3d</b></span>
    </footer>
  </section>
</main>

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

// 패럴랙스 3층 — 먼 별·중간 언덕·앞 글자가 각기 다른 계수로 translate3d 로 움직인다
// 미리보기(.is-demo)는 CSS 키프레임이 스크롤을 대신하고, 손이 닿으면 JS 의 rAF 루프가 lerp 로 이어받는다
$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-ink);

.px {
  position: relative;
  box-sizing: border-box;
  width: min(320px, 92vw);
  border-radius: $r-card;
  background: $subject-cream;
  color: $subject-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.px__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
}
.px__title {
  margin: 0;
  font-size: 13px;
  font-weight: 800;
  line-height: 1.3;
}
.px__attr {
  margin: 0;
  font-size: 10px;
  line-height: 1.3;
  color: rgba($subject-ink, .72);
  code { font-family: "Consolas", "Menlo", monospace; }
}

// 스크롤 상자(view)와 씬(scene)은 분리 — transform 은 언제나 씬 안 층에만 건다 (051 함정)
.px__view {
  position: relative;
  height: 168px;
  overflow-y: auto;
  background: $tick-panel;
  outline: none;
}
.px__scene {
  position: sticky;
  top: 0;
  height: 100%;
}
// 스크롤 여유 — 이 세로 폭이 곧 스크롤 범위(120px)다
.px__spacer { height: 120px; }

.px__layer {
  position: absolute;
  will-change: transform;
}
// 먼 별 — 44px 타일로 뿌린 점과 달. 가장 느린 계수를 받는다 (이동 14.4px + 여유)
.px__layer--stars {
  inset: -24px 0;
  background-image:
    radial-gradient(circle 1.5px at 12px 12px, rgba($subject-cream, .9) 99%, transparent 100%),
    radial-gradient(circle 1px at 30px 26px, rgba($subject-cream, .5) 99%, transparent 100%),
    radial-gradient(circle 2px at 36px 8px, rgba($subject-cream, .75) 99%, transparent 100%);
  background-size: 44px 44px;
  &::after {
    content: "";
    position: absolute;
    top: 44px;
    right: 32px;
    width: 18px;
    height: 18px;
    border-radius: 50%;
    background: rgba($subject-cream, .92);
    box-shadow: 0 0 12px rgba($subject-cream, .4);
  }
}
// 중간 언덕 — 두 겹의 언덕이 밑에서 올라온다 (이동 36px + 여유)
.px__layer--hills {
  inset: -44px 0;
  .px__hills {
    position: absolute;
    bottom: 0;
    left: 0;
    display: block;
    width: 100%;
    height: 132px;
  }
  .px__hill--back { fill: $subject-blue; }
  .px__hill--front { fill: $subject-blue-deep; }
}
// 앞 글자 — 가장 빠른 계수. 씬 중심보다 낮게 시작해 위로 지나간다 (이동 66px + 여유)
.px__layer--type {
  inset: -72px 0;
  display: grid;
  place-items: center;
}
.px__word {
  margin: $sp-8 0 0;
  font-size: 30px;
  font-weight: 800;
  line-height: 1.1;
  letter-spacing: .14em;
  color: $subject-cream;
}

.px__foot {
  display: flex;
  align-items: center;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
  border-top: 1px solid rgba($subject-ink, .12);
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  b { color: $subject-orange-deep; }
}
.px__dot {
  width: 8px;
  height: 8px;
  border-radius: $r-pill;
  background: $color;
}

.px__view:focus-visible {
  outline: 2px solid $color;
  outline-offset: -2px;
}

// 미리보기 — 스크롤을 대신해 세 층이 계수 비율 그대로 미끄러진다 (계수 곱하기 범위 120: 14.4 대 36 대 66)
.px.is-demo {
  .px__layer--stars  { animation-name: px-far;  animation-duration: $duration; animation-timing-function: $easing; animation-iteration-count: infinite; }
  .px__layer--hills  { animation-name: px-mid;  animation-duration: $duration; animation-timing-function: $easing; animation-iteration-count: infinite; }
  .px__layer--type   { animation-name: px-near; animation-duration: $duration; animation-timing-function: $easing; animation-iteration-count: infinite; }
  .px__dot {
    animation-name: px-blink;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
}

@keyframes px-far  { 0%, 8% { transform: translate3d(0, 0, 0); } 36%, 56% { transform: translate3d(0, -14.4px, 0); } 82%, 100% { transform: translate3d(0, 0, 0); } }
@keyframes px-mid  { 0%, 8% { transform: translate3d(0, 0, 0); } 36%, 56% { transform: translate3d(0, -36px, 0); } 82%, 100% { transform: translate3d(0, 0, 0); } }
@keyframes px-near { 0%, 8% { transform: translate3d(0, 0, 0); } 36%, 56% { transform: translate3d(0, -66px, 0); } 82%, 100% { transform: translate3d(0, 0, 0); } }
@keyframes px-blink {
  0% { background: rgba($subject-ink, .2); }
  36% { background: $color; }
  86% { background: rgba($subject-ink, .2); }
}

@media (max-width: 340px) {
  .px { width: 100%; }
  .px__head,
  .px__foot { padding: $sp-1 $sp-2; }
  .px__view { height: 112px; }
  .px__word { margin-top: 28px; font-size: 24px; }
  .px__layer--hills .px__hills { height: 100px; }
}

@media (prefers-reduced-motion: reduce) {
  .px__layer { transition: none !important; }
  .px.is-demo .px__layer,
  .px.is-demo .px__dot { animation: none !important; }
  // 정지 상태 — 세 층이 제자리에서 온전히 보인다
  .px.is-demo .px__layer { transform: none !important; }
  .px.is-demo .px__dot { background: $color !important; }
}

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);
}

.px {
  position: relative;
  box-sizing: border-box;
  width: min(320px, 92vw);
  border-radius: 16px;
  background: #fff7e6;
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.px__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
  padding: 8px 12px;
}

.px__title {
  margin: 0;
  font-size: 13px;
  font-weight: 800;
  line-height: 1.3;
}

.px__attr {
  margin: 0;
  font-size: 10px;
  line-height: 1.3;
  color: rgba(23, 20, 26, 0.72);
}
.px__attr code {
  font-family: "Consolas", "Menlo", monospace;
}

.px__view {
  position: relative;
  height: 168px;
  overflow-y: auto;
  background: #231f28;
  outline: none;
}

.px__scene {
  position: sticky;
  top: 0;
  height: 100%;
}

.px__spacer {
  height: 120px;
}

.px__layer {
  position: absolute;
  will-change: transform;
}

.px__layer--stars {
  inset: -24px 0;
  background-image: radial-gradient(circle 1.5px at 12px 12px, rgba(255, 247, 230, 0.9) 99%, transparent 100%), radial-gradient(circle 1px at 30px 26px, rgba(255, 247, 230, 0.5) 99%, transparent 100%), radial-gradient(circle 2px at 36px 8px, rgba(255, 247, 230, 0.75) 99%, transparent 100%);
  background-size: 44px 44px;
}
.px__layer--stars::after {
  content: "";
  position: absolute;
  top: 44px;
  right: 32px;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: rgba(255, 247, 230, 0.92);
  box-shadow: 0 0 12px rgba(255, 247, 230, 0.4);
}

.px__layer--hills {
  inset: -44px 0;
}
.px__layer--hills .px__hills {
  position: absolute;
  bottom: 0;
  left: 0;
  display: block;
  width: 100%;
  height: 132px;
}
.px__layer--hills .px__hill--back {
  fill: #2f6df6;
}
.px__layer--hills .px__hill--front {
  fill: #0a4fe8;
}

.px__layer--type {
  inset: -72px 0;
  display: grid;
  place-items: center;
}

.px__word {
  margin: 32px 0 0;
  font-size: 30px;
  font-weight: 800;
  line-height: 1.1;
  letter-spacing: 0.14em;
  color: #fff7e6;
}

.px__foot {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-top: 1px solid rgba(23, 20, 26, 0.12);
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
}
.px__foot b {
  color: #c93000;
}

.px__dot {
  width: 8px;
  height: 8px;
  border-radius: 999px;
  background: #2f6df6;
}

.px__view:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: -2px;
}

.px.is-demo .px__layer--stars {
  animation-name: px-far;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}
.px.is-demo .px__layer--hills {
  animation-name: px-mid;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}
.px.is-demo .px__layer--type {
  animation-name: px-near;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}
.px.is-demo .px__dot {
  animation-name: px-blink;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

@keyframes px-far {
  0%, 8% {
    transform: translate3d(0, 0, 0);
  }
  36%, 56% {
    transform: translate3d(0, -14.4px, 0);
  }
  82%, 100% {
    transform: translate3d(0, 0, 0);
  }
}
@keyframes px-mid {
  0%, 8% {
    transform: translate3d(0, 0, 0);
  }
  36%, 56% {
    transform: translate3d(0, -36px, 0);
  }
  82%, 100% {
    transform: translate3d(0, 0, 0);
  }
}
@keyframes px-near {
  0%, 8% {
    transform: translate3d(0, 0, 0);
  }
  36%, 56% {
    transform: translate3d(0, -66px, 0);
  }
  82%, 100% {
    transform: translate3d(0, 0, 0);
  }
}
@keyframes px-blink {
  0% {
    background: rgba(23, 20, 26, 0.2);
  }
  36% {
    background: #2f6df6;
  }
  86% {
    background: rgba(23, 20, 26, 0.2);
  }
}
@media (max-width: 340px) {
  .px {
    width: 100%;
  }
  .px__head,
  .px__foot {
    padding: 4px 8px;
  }
  .px__view {
    height: 112px;
  }
  .px__word {
    margin-top: 28px;
    font-size: 24px;
  }
  .px__layer--hills .px__hills {
    height: 100px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .px__layer {
    transition: none !important;
  }
  .px.is-demo .px__layer,
  .px.is-demo .px__dot {
    animation: none !important;
  }
  .px.is-demo .px__layer {
    transform: none !important;
  }
  .px.is-demo .px__dot {
    background: #2f6df6 !important;
  }
}

// Three-layer parallax — 스크롤 위치를 매 프레임 lerp 로 좇아 층마다 다른 계수로 translate3d 를 건다
var root = document.getElementById('px');
var view = document.getElementById('px-view');
var layers = Array.prototype.slice.call(document.querySelectorAll('.px__layer'));
var current = 0;
var started = false;

function lerp(a, b, t) {
  return a + (b - a) * t;
}

function frame() {
  var target = view.scrollTop;
  // 매 프레임 목표의 12 퍼센트씩 다가가므로 빠른 스크롤에도 끊기지 않고, 0.1px 안으로 좁혀지면 딱 맞춘다
  current = Math.abs(target - current) < 0.1 ? target : lerp(current, target, 0.12);
  for (var i = 0; i < layers.length; i++) {
    var rate = parseFloat(layers[i].getAttribute('data-rate')) || 0;
    layers[i].style.transform = 'translate3d(0, ' + (-current * rate).toFixed(2) + 'px, 0)';
  }
  requestAnimationFrame(frame);
}

function start() {
  root.classList.remove('is-demo');
  if (started) return;
  started = true;
  requestAnimationFrame(frame);
}
view.addEventListener('scroll', start, { passive: true });
view.addEventListener('pointerdown', start);
view.addEventListener('keydown', function (e) {
  if (e.key === 'ArrowDown' || e.key === 'ArrowUp' || e.key === 'PageDown' || e.key === 'PageUp' || e.key === ' ') start();
});

import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./ParallaxRatioLayers.module.scss";

export type ParallaxRatioLayersProps = {
  title?: string;
  attr?: string;
  state?: string;
  stateBold?: string;
  word?: string;
  groupLabel?: string;
  sceneLabel?: string;
  rates?: number[];
  /** 격자 미리보기용 2초 자동 루프. 사람이 손대면 꺼진다 */
  demo?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
// ambient 가 얇아 DOM 요소 타입을 못 쓴다 — 필요한 꼴만 로컬 타입으로 선언
type Box<T> = { current: T };
type KeyEvt = { key: string };

function lerp(a: number, b: number, t: number) {
  return a + (b - a) * t;
}

export default function ParallaxRatioLayers({
  title = "패럴랙스 3층",
  attr = "lerp(cur, tgt, 0.12)",
  state = "세 층이 각기 다른 계수로",
  stateBold = "translate3d",
  word = "SCROLL",
  groupLabel = "패럴랙스 3층 데모",
  sceneLabel = "별과 언덕과 글자 씬 — 스크롤하면 층마다 다른 거리로 움직입니다",
  rates = [0.12, 0.3, 0.55],
  demo = true,
  duration = 2000,
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#2f6df6",
}: ParallaxRatioLayersProps) {
  const [live, setLive] = useState(demo);
  const viewRef = useRef<HTMLDivElement>(null) as unknown as Box<HTMLDivElement | null>;
  const layerRefs = useRef<(HTMLElement | null)[]>([]) as unknown as Box<(HTMLElement | null)[]>;

  useEffect(() => {
    if (live) return;
    const view = viewRef.current;
    if (!view) return;
    let raf = 0;
    let current = 0;
    // 매 프레임 목표의 12 퍼센트씩 다가가 0.1px 안으로 좁혀지면 딱 맞춘다
    const tick = () => {
      const target = view.scrollTop;
      current = Math.abs(target - current) < 0.1 ? target : lerp(current, target, 0.12);
      layerRefs.current.forEach((el) => {
        if (!el) return;
        const rate = parseFloat(el.getAttribute("data-rate") || "0") || 0;
        el.style.transform = `translate3d(0, ${(-current * rate).toFixed(2)}px, 0)`;
      });
      raf = requestAnimationFrame(tick);
    };
    raf = requestAnimationFrame(tick);
    return () => cancelAnimationFrame(raf);
  }, [live]);

  const vars: Vars = {
    "--duration": `${duration}ms`,
    "--easing": easing,
    "--color": color,
  };
  const layerClass = [styles.layerStars, styles.layerHills, styles.layerType];

  return (
    <section
      className={`${styles.px} ${live ? styles.isDemo : ""}`}
      style={vars}
      aria-label={groupLabel}
    >
      <header className={styles.head}>
        <p className={styles.title}>{title}</p>
        <p className={styles.attr}><code>{attr}</code></p>
      </header>
      <div
        className={styles.view}
        ref={viewRef as unknown as Box<HTMLDivElement>}
        onScroll={() => setLive(false)}
        onPointerDown={() => setLive(false)}
        onKeyDown={(e: KeyEvt) => {
          if (e.key === "ArrowDown" || e.key === "ArrowUp" || e.key === "PageDown" || e.key === "PageUp" || e.key === " ") setLive(false);
        }}
        tabIndex={0}
        role="region"
        aria-label={sceneLabel}
      >
        <div className={styles.scene}>
          <div className={`${styles.layer} ${layerClass[0]}`} data-rate={rates[0]} aria-hidden="true" />
          <div className={`${styles.layer} ${layerClass[1]}`} data-rate={rates[1]} aria-hidden="true">
            <svg className={styles.hills} viewBox="0 0 320 130" preserveAspectRatio="none">
              <path className={styles.hillBack} d="M0 130 L0 72 C 34 30, 84 16, 128 46 C 168 74, 206 78, 244 62 C 276 48, 302 52, 320 60 L320 130 Z" />
              <path className={styles.hillFront} d="M0 130 L0 100 C 50 62, 100 68, 148 88 C 198 110, 250 92, 320 70 L320 130 Z" />
            </svg>
          </div>
          <div className={`${styles.layer} ${layerClass[2]}`} data-rate={rates[2]}>
            <p className={styles.word}>{word}</p>
          </div>
        </div>
        <div className={styles.spacer} aria-hidden="true" />
      </div>
      <footer className={styles.foot}>
        <span className={styles.dot} aria-hidden="true" />
        <span className={styles.state}>
          {state} <b>{stateBold}</b>
        </span>
      </footer>
    </section>
  );
}