09Focus and tilt values linked — as the field's focus-position value moves, the card visual's tilt value follows along

<main class="stage">
<div class="ct is-demo" id="ct">
  <div class="ct__pad" id="ctPad">
    <div class="ct__card" id="ctCard">
      <span class="ct__chip"></span>
      <span class="ct__num">9999 9999 9999 9995</span>
      <span class="ct__sheen" id="ctSheen"></span>
    </div>
  </div>
</div>
</main>

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

// 계산 겹: 포인터 좌표 값 → 목표 기울기 값을 매 프레임 LERP 비율만큼만 따라가는 관성 보간(index.html).
@include stage($stage-ink);

.ct {
  width: 100%;
  max-width: 300px;
}

.ct__pad {
  width: 100%;
  height: 168px;
  display: grid;
  place-items: center;
  touch-action: none;
}

.ct__card {
  position: relative;
  width: 220px;
  height: 132px;
  border-radius: $r-card;
  background: $subject-cream;
  box-shadow: $shadow-raised;
  display: grid;
  align-content: space-between;
  padding: $sp-4;
  box-sizing: border-box;
  overflow: hidden;
  will-change: transform;
}

.ct__chip {
  width: 28px;
  height: 20px;
  border-radius: $r-xs;
  background: rgba($subject-ink, .78);
}

.ct__num {
  font-family: "SFMono-Regular", Consolas, monospace;
  font-weight: 600;
  font-size: 14px;
  letter-spacing: .04em;
  color: $subject-ink;
}

.ct__sheen {
  position: absolute;
  inset: -40%;
  background: radial-gradient(circle, rgba($subject-blue-light, .35), transparent 60%);
  pointer-events: none;
}

@media (max-width: 340px) {
  .ct__card { width: 190px; height: 114px; }
  .ct__pad { height: 148px; }
}

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

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);
}

.ct {
  width: 100%;
  max-width: 300px;
}

.ct__pad {
  width: 100%;
  height: 168px;
  display: grid;
  place-items: center;
  touch-action: none;
}

.ct__card {
  position: relative;
  width: 220px;
  height: 132px;
  border-radius: 16px;
  background: #fff7e6;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  display: grid;
  align-content: space-between;
  padding: 16px;
  box-sizing: border-box;
  overflow: hidden;
  will-change: transform;
}

.ct__chip {
  width: 28px;
  height: 20px;
  border-radius: 4px;
  background: rgba(23, 20, 26, 0.78);
}

.ct__num {
  font-family: "SFMono-Regular", Consolas, monospace;
  font-weight: 600;
  font-size: 14px;
  letter-spacing: 0.04em;
  color: #17141a;
}

.ct__sheen {
  position: absolute;
  inset: -40%;
  background: radial-gradient(circle, rgba(91, 140, 248, 0.35), transparent 60%);
  pointer-events: none;
}

@media (max-width: 340px) {
  .ct__card {
    width: 190px;
    height: 114px;
  }
  .ct__pad {
    height: 148px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ct__card, .ct__sheen {
    transition: none;
  }
}

(function () {
  var root = document.getElementById('ct');
  var pad = document.getElementById('ctPad');
  var card = document.getElementById('ctCard');
  var sheen = document.getElementById('ctSheen');
  var MAX_DEG = 14;
  var LERP = 0.14; // 계산 겹: 목표 기울기 값으로 매 프레임 이 비율만큼만 다가가는 관성 보간

  var targetX = 0, targetY = 0, curX = 0, curY = 0;
  var raf = null;

  function apply() {
    curX += (targetX - curX) * LERP;
    curY += (targetY - curY) * LERP;
    card.style.transform = 'perspective(600px) rotateX(' + curX.toFixed(2) + 'deg) rotateY(' + curY.toFixed(2) + 'deg)';
    sheen.style.transform = 'translate(' + (curY * 1.4).toFixed(1) + 'px,' + (curX * -1.4).toFixed(1) + 'px)';
    raf = requestAnimationFrame(apply);
  }
  raf = requestAnimationFrame(apply);

  function setTargetFromPoint(px, py) {
    var r = pad.getBoundingClientRect();
    var nx = (px - r.left) / r.width - 0.5;
    var ny = (py - r.top) / r.height - 0.5;
    targetY = nx * MAX_DEG * 2;
    targetX = -ny * MAX_DEG * 2;
  }

  pad.addEventListener('pointermove', function (e) {
    root.classList.remove('is-demo');
    stopAutoplay();
    setTargetFromPoint(e.clientX, e.clientY);
  });
  pad.addEventListener('pointerleave', function () {
    if (autoTimer === null) { targetX = 0; targetY = 0; }
  });

  // 자동 루프: 포인터 좌표 값이 원을 그리며 도는 것을 흉내낸다.
  var t = 0;
  var autoTimer = null;
  function autoTick() {
    var r = pad.getBoundingClientRect();
    t += 0.12;
    var cx = r.left + r.width / 2 + Math.cos(t) * r.width * 0.32;
    var cy = r.top + r.height / 2 + Math.sin(t * 1.3) * r.height * 0.32;
    setTargetFromPoint(cx, cy);
  }
  function stopAutoplay() { if (autoTimer) { clearInterval(autoTimer); autoTimer = null; } }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (!reduce) { autoTimer = setInterval(autoTick, 60); }
})();

import { useEffect, useRef } from "react";
import styles from "./FocusTilt3d.module.scss";

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

const MAX_DEG = 14;
const LERP = 0.14; // 계산 겹: 목표 기울기 값으로 매 프레임 이 비율만큼만 다가가는 관성 보간

export default function FocusTilt3d() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement | null>;

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const pad = root.querySelector(`.${styles.pad}`) as HTMLElement | null;
    const card = root.querySelector(`.${styles.card}`) as HTMLElement | null;
    const sheen = root.querySelector(`.${styles.sheen}`) as HTMLElement | null;
    if (!pad || !card || !sheen) return;

    let targetX = 0, targetY = 0, curX = 0, curY = 0;
    let raf: number | null = null;

    function apply() {
      curX += (targetX - curX) * LERP;
      curY += (targetY - curY) * LERP;
      card!.style.transform = "perspective(600px) rotateX(" + curX.toFixed(2) + "deg) rotateY(" + curY.toFixed(2) + "deg)";
      sheen!.style.transform = "translate(" + (curY * 1.4).toFixed(1) + "px," + (curX * -1.4).toFixed(1) + "px)";
      raf = requestAnimationFrame(apply);
    }
    raf = requestAnimationFrame(apply);

    function setTargetFromPoint(px: number, py: number) {
      const r = pad!.getBoundingClientRect();
      const nx = (px - r.left) / r.width - 0.5;
      const ny = (py - r.top) / r.height - 0.5;
      targetY = nx * MAX_DEG * 2;
      targetX = -ny * MAX_DEG * 2;
    }

    function onPointerMove(e: PointerEvent) {
      root!.classList.remove(styles["is-demo"]);
      stopAutoplay();
      setTargetFromPoint(e.clientX, e.clientY);
    }
    function onPointerLeave() {
      if (autoTimer === null) { targetX = 0; targetY = 0; }
    }
    pad.addEventListener("pointermove", onPointerMove);
    pad.addEventListener("pointerleave", onPointerLeave);

    // 자동 루프: 포인터 좌표 값이 원을 그리며 도는 것을 흉내낸다.
    let t = 0;
    let autoTimer: number | null = null;
    function autoTick() {
      const r = pad!.getBoundingClientRect();
      t += 0.12;
      const cx = r.left + r.width / 2 + Math.cos(t) * r.width * 0.32;
      const cy = r.top + r.height / 2 + Math.sin(t * 1.3) * r.height * 0.32;
      setTargetFromPoint(cx, cy);
    }
    function stopAutoplay() {
      if (autoTimer !== null) { window.clearInterval(autoTimer); autoTimer = null; }
    }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { autoTimer = window.setInterval(autoTick, 60); }

    return () => {
      stopAutoplay();
      if (raf !== null) cancelAnimationFrame(raf);
      pad.removeEventListener("pointermove", onPointerMove);
      pad.removeEventListener("pointerleave", onPointerLeave);
    };
  }, []);

  return (
    <div ref={rootRef} className={`${styles.stage} ${styles.ct} ${styles["is-demo"]}`}>
      <div className={styles.pad}>
        <div className={styles.card}>
          <span className={styles.chip} />
          <span className={styles.num}>9999 9999 9999 9995</span>
          <span className={styles.sheen} />
        </div>
      </div>
    </div>
  );
}