04리본이 접히며 떨어지는 북마크 버튼

<main class="stage">
<div class="fd is-demo" id="fd">
  <p class="fd__caption">리본이 접히며 떨어지는 북마크 버튼</p>
  <div class="fd__scene" id="fdScene">
    <div class="fd__shadow" id="fdShadow" aria-hidden="true"></div>
    <button class="fd__btn" id="fdBtn" type="button" aria-pressed="false">
      <span class="fd__wrap" id="fdWrap">
        <svg class="fd__icon" viewBox="0 0 24 24" width="30" height="30" aria-hidden="true" focusable="false">
          <path class="fd__shape" d="M6.5 3A1.5 1.5 0 0 1 8 1.5h8A1.5 1.5 0 0 1 17.5 3v18.2a.9.9 0 0 1-1.38.76L12 19.1l-4.12 2.86A.9.9 0 0 1 6.5 21.2Z"/>
        </svg>
      </span>
    </button>
  </div>
  <p class="fd__status" id="fdStatus" aria-live="polite">저장 전</p>
</div>
</main>

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

// 값 하나: 접힘 진행률(사인 봉우리) → rotateX 접힘 각 + 낙하 거리 + 그림자 블러/농도.

$duration: $dur-enter;
$easing: $ease-out;
$color: $subject-orange-deep;

@include stage($stage-orange);

.fd {
  display: grid;
  gap: $sp-3;
  justify-items: center;
}

.fd__caption {
  margin: 0;
  font-size: 12px;
  font-weight: 600;
  color: $subject-ink;
}

.fd__scene {
  position: relative;
  width: 200px;
  height: 140px;
  display: grid;
  place-items: center;
  --tone: 0;
}

.fd__scene::before {
  content: "";
  position: absolute;
  inset: 0;
  margin: auto;
  width: 200px;
  height: 140px;
  border-radius: $r-card;
  background: radial-gradient(circle, rgba($subject-orange-deep, calc(.05 + var(--tone) * .72)) 0%, rgba($subject-orange-deep, calc(.02 + var(--tone) * .3)) 55%, transparent 88%);
  pointer-events: none;
}

.fd__shadow {
  position: absolute;
  bottom: 28px;
  width: 60px;
  height: 14px;
  border-radius: $r-pill;
  background: transparent;
  pointer-events: none;
}

.fd__btn {
  position: relative;
  z-index: 1;
  border: 0;
  background: $stage-paper;
  border-radius: $r-pill;
  padding: $sp-4;
  cursor: pointer;
  perspective: 300px;
}

.fd__btn:focus-visible {
  outline: 2px solid $subject-orange-deep;
  outline-offset: 3px;
}

.fd__wrap {
  display: block;
  transform-origin: top center;
  will-change: transform;
}

.fd__shape {
  fill: none;
  stroke: $color;
  stroke-width: 1.6;
  stroke-linejoin: round;
}

.fd.is-saved .fd__shape {
  fill: $color;
}

.fd__status {
  margin: 0;
  font-size: 11px;
  color: $subject-ink;
  font-weight: 600;
}

@media (max-width: 340px) {
  .fd__scene { width: 150px; height: 96px; }
  .fd__shadow { bottom: 14px; }
}

@media (prefers-reduced-motion: reduce) {
  .fd__wrap { transition: none; }
}

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);
}

.fd {
  display: grid;
  gap: 12px;
  justify-items: center;
}

.fd__caption {
  margin: 0;
  font-size: 12px;
  font-weight: 600;
  color: #17141a;
}

.fd__scene {
  position: relative;
  width: 200px;
  height: 140px;
  display: grid;
  place-items: center;
  --tone: 0;
}

.fd__scene::before {
  content: "";
  position: absolute;
  inset: 0;
  margin: auto;
  width: 200px;
  height: 140px;
  border-radius: 16px;
  background: radial-gradient(circle, rgba(201, 48, 0, calc(0.05 + var(--tone) * 0.72)) 0%, rgba(201, 48, 0, calc(0.02 + var(--tone) * 0.3)) 55%, transparent 88%);
  pointer-events: none;
}

.fd__shadow {
  position: absolute;
  bottom: 28px;
  width: 60px;
  height: 14px;
  border-radius: 999px;
  background: transparent;
  pointer-events: none;
}

.fd__btn {
  position: relative;
  z-index: 1;
  border: 0;
  background: #ffffff;
  border-radius: 999px;
  padding: 16px;
  cursor: pointer;
  perspective: 300px;
}

.fd__btn:focus-visible {
  outline: 2px solid #c93000;
  outline-offset: 3px;
}

.fd__wrap {
  display: block;
  transform-origin: top center;
  will-change: transform;
}

.fd__shape {
  fill: none;
  stroke: #c93000;
  stroke-width: 1.6;
  stroke-linejoin: round;
}

.fd.is-saved .fd__shape {
  fill: #c93000;
}

.fd__status {
  margin: 0;
  font-size: 11px;
  color: #17141a;
  font-weight: 600;
}

@media (max-width: 340px) {
  .fd__scene {
    width: 150px;
    height: 96px;
  }
  .fd__shadow {
    bottom: 14px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .fd__wrap {
    transition: none;
  }
}

(function () {
  "use strict";

  var FOLD_MAX_DEG = 56;
  var FOLD_DROP_MAX_PX = 12;
  var FOLD_MS = 560;
  var CYCLE_S = 2;

  var root = document.getElementById("fd");
  var scene = document.getElementById("fdScene");
  var shadow = document.getElementById("fdShadow");
  var btn = document.getElementById("fdBtn");
  var wrap = document.getElementById("fdWrap");
  var status = document.getElementById("fdStatus");
  var reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

  var saved = false;
  function setSaved(v) {
    saved = v;
    btn.setAttribute("aria-pressed", String(v));
    root.classList.toggle("is-saved", v);
    status.textContent = v ? "저장됨" : "저장 전";
  }

  // 값 하나: 접힘 진행률 p(0~1, 사인 곡선 한 번의 봉우리) → 접힘 각도(rotateX) + 낙하 거리
  // + 그림자 블러·투명도(높이가 낮아질수록 그림자가 진해진다).
  function render(p) {
    scene.style.setProperty("--tone", p.toFixed(3));
    var deg = p * FOLD_MAX_DEG;
    var drop = p * FOLD_DROP_MAX_PX;
    wrap.style.transform = "perspective(300px) rotateX(" + deg.toFixed(2) + "deg) translateY(" + drop.toFixed(2) + "px)";
    var blur = 3 + p * 10;
    var spread = 6 - p * 4;
    var alpha = 0.22 + p * 0.28;
    shadow.style.boxShadow = "0 " + (2 + p * 6).toFixed(1) + "px " + blur.toFixed(1) + "px " + spread.toFixed(1) + "px rgba(23,20,26," + alpha.toFixed(2) + ")";
    shadow.style.transform = "scaleX(" + (1 - p * 0.18).toFixed(3) + ")";
  }

  var foldStart = null;
  var pending = false;

  function triggerFold() {
    pending = true;
  }

  btn.addEventListener("click", function () {
    root.classList.remove("is-demo");
    setSaved(!saved);
    triggerFold();
  });

  var start = null;
  var prevT = 0;
  var toggledA = false;
  var toggledB = false;
  function loop(now) {
    if (start === null) start = now;
    if (pending) { foldStart = now; pending = false; }
    var t = ((now - start) / 1000) % CYCLE_S;
    if (t < prevT) { toggledA = false; toggledB = false; }
    prevT = t;
    if (!reduce && root.classList.contains("is-demo")) {
      if (!toggledA && t > 0.35) { toggledA = true; setSaved(true); triggerFold(); }
      if (!toggledB && t > 1.35) { toggledB = true; setSaved(false); triggerFold(); }
    }
    var p = 0;
    if (!reduce && foldStart !== null) {
      var ft = (now - foldStart) / FOLD_MS;
      if (ft >= 1) {
        foldStart = null;
        p = 0;
      } else {
        p = Math.sin(Math.PI * ft);
      }
    }
    render(p);
    requestAnimationFrame(loop);
  }

  requestAnimationFrame(loop);
})();

// RibbonFoldDropBookmark — vanilla 판(run/416/demo/04-bookmark-btn-ribbon-fold-drop/index.html) 의 React 포트.
// 값 하나: 접힘 진행률(사인 곡선 한 번의 봉우리) → 접힘 각도(rotateX) + 낙하 거리 + 그림자 블러·농도 + 배경 톤.
import { useEffect, useRef, useState } from "react";
import styles from "./RibbonFoldDropBookmark.module.scss";

type Box<T> = { current: T };

const FOLD_MAX_DEG = 56;
const FOLD_DROP_MAX_PX = 12;
const FOLD_MS = 560;
const CYCLE_S = 2;

export default function RibbonFoldDropBookmark() {
  const sceneRef = useRef<HTMLDivElement | null>(null);
  const shadowRef = useRef<HTMLDivElement | null>(null);
  const wrapRef = useRef<HTMLSpanElement | null>(null);
  const foldStartRef = useRef<number | null>(null);
  const pendingRef = useRef<boolean>(false) as Box<boolean>;
  const frameRef = useRef<number>(0) as Box<number>;
  const [saved, setSaved] = useState(false);
  const [demo, setDemo] = useState(true);
  const [reduce, setReduce] = useState(false);

  function render(p: number): void {
    const scene = sceneRef.current;
    const wrap = wrapRef.current;
    const shadow = shadowRef.current;
    if (!scene || !wrap || !shadow) return;
    scene.style.setProperty("--tone", p.toFixed(3));
    const deg = p * FOLD_MAX_DEG;
    const drop = p * FOLD_DROP_MAX_PX;
    wrap.style.transform = "perspective(300px) rotateX(" + deg.toFixed(2) + "deg) translateY(" + drop.toFixed(2) + "px)";
    const blur = 3 + p * 10;
    const spread = 6 - p * 4;
    const alpha = 0.22 + p * 0.28;
    shadow.style.boxShadow = "0 " + (2 + p * 6).toFixed(1) + "px " + blur.toFixed(1) + "px " + spread.toFixed(1) + "px rgba(23,20,26," + alpha.toFixed(2) + ")";
    shadow.style.transform = "scaleX(" + (1 - p * 0.18).toFixed(3) + ")";
  }

  function triggerFold(): void {
    pendingRef.current = true;
  }

  useEffect(() => {
    setReduce(window.matchMedia("(prefers-reduced-motion: reduce)").matches);
  }, []);

  useEffect(() => {
    let start = 0;
    let prevT = 0;
    let toggledA = false;
    let toggledB = false;
    function loop(now: number): void {
      if (start === 0) start = now;
      if (pendingRef.current) { foldStartRef.current = now; pendingRef.current = false; }
      const t = ((now - start) / 1000) % CYCLE_S;
      if (t < prevT) { toggledA = false; toggledB = false; }
      prevT = t;
      if (!reduce && demo) {
        if (!toggledA && t > 0.35) { toggledA = true; setSaved(true); triggerFold(); }
        if (!toggledB && t > 1.35) { toggledB = true; setSaved(false); triggerFold(); }
      }
      let p = 0;
      if (!reduce && foldStartRef.current !== null) {
        const ft = (now - foldStartRef.current) / FOLD_MS;
        if (ft >= 1) {
          foldStartRef.current = null;
          p = 0;
        } else {
          p = Math.sin(Math.PI * ft);
        }
      }
      render(p);
      frameRef.current = requestAnimationFrame(loop);
    }
    frameRef.current = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(frameRef.current);
  }, [reduce, demo]);

  function onClick(): void {
    setDemo(false);
    setSaved(!saved);
    triggerFold();
  }

  return (
    <main className={styles.stage}>
      <div className={styles.fd}>
        <p className={styles.caption}>리본이 접히며 떨어지는 북마크 버튼</p>
        <div className={styles.scene} ref={sceneRef}>
          <div className={styles.shadow} ref={shadowRef} aria-hidden="true" />
          <button className={styles.btn} type="button" aria-pressed={saved} onClick={onClick}>
            <span className={styles.wrap} ref={wrapRef}>
              <svg className={styles.icon} viewBox="0 0 24 24" width={30} height={30} aria-hidden="true" focusable="false">
                <path className={styles.shape} d="M6.5 3A1.5 1.5 0 0 1 8 1.5h8A1.5 1.5 0 0 1 17.5 3v18.2a.9.9 0 0 1-1.38.76L12 19.1l-4.12 2.86A.9.9 0 0 1 6.5 21.2Z" />
              </svg>
            </span>
          </button>
        </div>
        <p className={styles.status} aria-live="polite">{saved ? "저장됨" : "저장 전"}</p>
      </div>
    </main>
  );
}