08Velocity-skewed list

<main class="stage">
  <div class="vs is-demo">
    <div class="vs__scroll">
      <div class="vs__row"><span class="vs__thumb vs__thumb--1"></span><span class="vs__t">Scroll down fast</span></div>
      <div class="vs__row"><span class="vs__thumb vs__thumb--2"></span><span class="vs__t">Cards feel the speed</span></div>
      <div class="vs__row"><span class="vs__thumb vs__thumb--3"></span><span class="vs__t">Stop and they settle</span></div>
      <div class="vs__row"><span class="vs__thumb vs__thumb--4"></span><span class="vs__t">Scroll up too</span></div>
    </div>
  </div>
</main>

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

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

@include stage($stage-ink);

.vs {
  width: min(390px, 88vw);
  height: clamp(150px, 62vh, 216px);
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.vs__scroll {
  height: 100%;
  overflow-y: auto;
  padding: $sp-3;
  box-sizing: border-box;
  scrollbar-width: none;
  &::-webkit-scrollbar { display: none; }
}

.vs__row {
  display: flex;
  align-items: center;
  gap: $sp-3;
  margin-bottom: $sp-3;
  padding: $sp-3;
  border-radius: $r-card;
  background: rgba(255, 247, 230, .96);
  box-sizing: border-box;
  // ── 실제 동작: JS 가 --vel(스크롤 속도)을 넣으면 skewY 가 그 값을 받아 기울고,
  // 속도가 0 으로 줄면 같은 계산식이 저절로 제자리로 돌려놓는다 ──
  transform: skewY(calc(var(--vel, 0) * -0.18deg));
  &:last-child { margin-bottom: 0; }
}

.vs__thumb {
  flex: 0 0 auto;
  width: 40px;
  height: 40px;
  border-radius: $r-sm;
}
.vs__thumb--1 { background: linear-gradient(135deg, $color, #d6ddeb); }
.vs__thumb--2 { background: linear-gradient(135deg, #c2ae82, $stage-yellow); }
.vs__thumb--3 { background: linear-gradient(135deg, $stage-orange, #ebdbd6); }
.vs__thumb--4 { background: linear-gradient(135deg, #37b786, #d6ebe2); }

.vs__t {
  color: #3c4750;
  font: 700 13px/1.4 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

// 데모 루프: 실제 스크롤 대신 카드가 왕복으로 기울었다 펴지는 걸 흉내(캡처용)
.vs.is-demo .vs__row { animation: vs-skew $duration $easing infinite; }
.vs.is-demo .vs__row:nth-child(2) { animation-delay: 40ms; }
.vs.is-demo .vs__row:nth-child(3) { animation-delay: 80ms; }
.vs.is-demo .vs__row:nth-child(4) { animation-delay: 120ms; }
@keyframes vs-skew {
  0%, 100% { transform: skewY(0deg); }
  30%      { transform: skewY(-4.4deg); }
  62%      { transform: skewY(2.2deg); }
}

@media (prefers-reduced-motion: reduce) {
  .vs.is-demo .vs__row { animation: none !important; }
  .vs__row { transform: none !important; } // 움직임 잠금: 속도 반응도 함께 끈다
  .vs__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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.vs {
  width: min(390px, 88vw);
  height: clamp(150px, 62vh, 216px);
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.vs__scroll {
  height: 100%;
  overflow-y: auto;
  padding: 12px;
  box-sizing: border-box;
  scrollbar-width: none;
}
.vs__scroll::-webkit-scrollbar {
  display: none;
}

.vs__row {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 12px;
  padding: 12px;
  border-radius: 16px;
  background: rgba(255, 247, 230, 0.96);
  box-sizing: border-box;
  transform: skewY(calc(var(--vel, 0) * -0.18deg));
}
.vs__row:last-child {
  margin-bottom: 0;
}

.vs__thumb {
  flex: 0 0 auto;
  width: 40px;
  height: 40px;
  border-radius: 8px;
}

.vs__thumb--1 {
  background: linear-gradient(135deg, #2f6df6, #d6ddeb);
}

.vs__thumb--2 {
  background: linear-gradient(135deg, #c2ae82, #ffd23f);
}

.vs__thumb--3 {
  background: linear-gradient(135deg, #ff4d1f, #ebdbd6);
}

.vs__thumb--4 {
  background: linear-gradient(135deg, #37b786, #d6ebe2);
}

.vs__t {
  color: #3c4750;
  font: 700 13px/1.4 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.vs.is-demo .vs__row {
  animation: vs-skew 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.vs.is-demo .vs__row:nth-child(2) {
  animation-delay: 40ms;
}

.vs.is-demo .vs__row:nth-child(3) {
  animation-delay: 80ms;
}

.vs.is-demo .vs__row:nth-child(4) {
  animation-delay: 120ms;
}

@keyframes vs-skew {
  0%, 100% {
    transform: skewY(0deg);
  }
  30% {
    transform: skewY(-4.4deg);
  }
  62% {
    transform: skewY(2.2deg);
  }
}
@media (prefers-reduced-motion: reduce) {
  .vs.is-demo .vs__row {
    animation: none !important;
  }
  .vs__row {
    transform: none !important;
  }
  .vs__scroll {
    scroll-behavior: auto;
  }
}

// 스크롤 속도를 재서 --vel 변수에 넣는다. 나머지는 CSS 계산(calc)이 한다.
// 미리보기(.is-demo) 중에는 CSS 키프레임이 움직임을 맡는다.
(function () {
  var box = document.querySelector('.vs__scroll');
  var last = box.scrollTop, vel = 0;
  box.addEventListener('scroll', function () {
    document.querySelector('.vs').classList.remove('is-demo');
    vel = Math.max(-24, Math.min(24, box.scrollTop - last));
    last = box.scrollTop;
  });
  (function decay() {
    vel *= 0.86;
    box.style.setProperty('--vel', vel.toFixed(2));
    requestAnimationFrame(decay);
  })();
})();

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

export type VelocitySkewProps = {
  duration?: number;
  easing?: string;
  color?: string;
  rows?: string[];
};

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

export default function VelocitySkew({
  duration = 300,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
  rows = ["빠르게 내려보세요", "카드가 속도를 느낍니다", "멈추면 제자리", "다시 올려도 돼요"],
}: VelocitySkewProps) {
  const boxRef = useRef<HTMLDivElement>(null);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  // 스크롤 속도를 재서 --vel 에 넣는다. 나머지는 CSS calc(skewY) 가 한다
  useEffect(() => {
    const box = boxRef.current;
    if (!box) return;
    let last = box.scrollTop;
    let vel = 0;
    let raf = 0;
    const onScroll = () => {
      vel = Math.max(-24, Math.min(24, box.scrollTop - last));
      last = box.scrollTop;
    };
    const decay = () => {
      vel *= 0.86;
      box.style.setProperty("--vel", vel.toFixed(2));
      raf = requestAnimationFrame(decay);
    };
    box.addEventListener("scroll", onScroll, { passive: true });
    raf = requestAnimationFrame(decay);
    return () => {
      box.removeEventListener("scroll", onScroll);
      cancelAnimationFrame(raf);
    };
  }, []);

  return (
    <div className={styles.vs} style={vars}>
      <div ref={boxRef} className={styles.scroll}>
        {rows.map((t, i) => (
          <div key={i} className={styles.row}>
            <span className={`${styles.thumb} ${styles["thumb" + ((i % 4) + 1)]}`} />
            <span className={styles.t}>{t}</span>
          </div>
        ))}
      </div>
    </div>
  );
}