03Tilting Button Whose Distance Value Becomes an Angle Value

<main class="stage">
<div class="ta is-demo" id="ta">
  <p class="ta__badge" id="taBadge">Angle value 0°</p>
  <div class="ta__scene" id="taScene">
    <button class="ta__btn" id="taBtn" type="button">
      <span class="ta__label">Buy now</span>
    </button>
  </div>
</div>
</main>

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

// 핵심: 커서–버튼 중심 방향 벡터를 단위 벡터로 정규화하고 atan2 로 각도를 구한 뒤,
// 거리 값(가까울수록 1)을 그 각도의 크기로 곱한다 — 닿기 전부터 커서 쪽으로 미리 기운다.

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

@include stage($stage-orange);

.ta {
  display: grid;
  gap: $sp-4;
  justify-items: center;
}

.ta__badge {
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .1);
  color: $subject-ink;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.ta__scene {
  perspective: 600px;
  padding: $sp-10;
}

.ta__btn {
  position: relative;
  border: 0;
  cursor: pointer;
  padding: $sp-4 $sp-8;
  border-radius: $r-control;
  background: $color;
  color: $subject-ink;
  font-size: 16px;
  font-weight: 700;
  transform-style: preserve-3d;
  box-shadow: $shadow-raised;
  will-change: transform, box-shadow;
  --hl-x: 50%;
  --hl-y: 50%;
  --hl-o: 0;
}

.ta__btn::before {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: radial-gradient(circle at var(--hl-x) var(--hl-y), rgba(23, 20, 26, .55), transparent 62%);
  opacity: var(--hl-o);
  pointer-events: none;
}

.ta__btn:focus-visible {
  outline: 2px solid $subject-ink;
  outline-offset: 3px;
}

@media (max-width: 340px) {
  .ta__scene { padding: $sp-6; }
  .ta__btn { padding: $sp-3 $sp-6; font-size: 14px; }
}

@media (prefers-reduced-motion: reduce) {
  .ta__btn { 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);
}

.ta {
  display: grid;
  gap: 16px;
  justify-items: center;
}

.ta__badge {
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.1);
  color: #17141a;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.ta__scene {
  perspective: 600px;
  padding: 40px;
}

.ta__btn {
  position: relative;
  border: 0;
  cursor: pointer;
  padding: 16px 32px;
  border-radius: 12px;
  background: #fff7e6;
  color: #17141a;
  font-size: 16px;
  font-weight: 700;
  transform-style: preserve-3d;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  will-change: transform, box-shadow;
  --hl-x: 50%;
  --hl-y: 50%;
  --hl-o: 0;
}

.ta__btn::before {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: radial-gradient(circle at var(--hl-x) var(--hl-y), rgba(23, 20, 26, 0.55), transparent 62%);
  opacity: var(--hl-o);
  pointer-events: none;
}

.ta__btn:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 3px;
}

@media (max-width: 340px) {
  .ta__scene {
    padding: 24px;
  }
  .ta__btn {
    padding: 12px 24px;
    font-size: 14px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ta__btn {
    transition: none;
  }
}

(function () {
  var PROX_RADIUS_PX = 190;
  var TA_MAX_DEG = 12;
  var LERP = 0.16;

  var root = document.getElementById('ta');
  var scene = document.getElementById('taScene');
  var btn = document.getElementById('taBtn');
  var badge = document.getElementById('taBadge');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function clamp(v, lo, hi) { return Math.max(lo, Math.min(hi, v)); }

  var targetDx = 0, targetDy = 0;
  var curDx = 0, curDy = 0;
  var hasPointer = false;

  function vectorToButton(x, y) {
    var r = btn.getBoundingClientRect();
    var cx = r.left + r.width / 2;
    var cy = r.top + r.height / 2;
    return [x - cx, y - cy];
  }

  function render(dx, dy) {
    // 방향 벡터 → 각도(atan2) 변환 — Distance value(가까울수록 1)을 각도 크기로 쓴다.
    var d = Math.hypot(dx, dy);
    var p = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
    var ux = d > 0.001 ? dx / d : 0;
    var uy = d > 0.001 ? dy / d : 0;
    var rotY = ux * p * TA_MAX_DEG;
    var rotX = -uy * p * TA_MAX_DEG;
    var lean = p * 6;
    btn.style.transform = 'translate(' + (ux * lean).toFixed(2) + 'px,' + (uy * lean).toFixed(2) + 'px) rotateX(' + rotX.toFixed(2) + 'deg) rotateY(' + rotY.toFixed(2) + 'deg)';
    // 계산 레이어: 같은 기울기 각도(ux·uy·p) 를 테두리 하이라이트 위치·깊이 그림자에도 전파한다.
    var shadowX = ux * p * 16;
    var shadowY = 6 + uy * p * 12;
    var shadowBlur = 14 + p * 22;
    btn.style.boxShadow = shadowX.toFixed(1) + 'px ' + shadowY.toFixed(1) + 'px ' + shadowBlur.toFixed(1) + 'px rgba(23,20,26,' + (0.2 + p * 0.3).toFixed(2) + ')';
    btn.style.setProperty('--hl-x', (50 + ux * 38).toFixed(1) + '%');
    btn.style.setProperty('--hl-y', (50 + uy * 38).toFixed(1) + '%');
    btn.style.setProperty('--hl-o', (0.12 + p * 0.5).toFixed(2));
    var angleDeg = Math.atan2(dy, dx) * 180 / Math.PI;
    badge.textContent = 'Angle value ' + Math.round(rotY) + '°';
    void angleDeg;
  }

  function syntheticOffset(t) {
    var ang = t * 1.9;
    var rad = 130 * (1 + Math.cos(t * Math.PI));
    return [Math.cos(ang) * rad, Math.sin(ang) * rad * 0.7];
  }

  var startTime = null;
  function loop(now) {
    if (startTime === null) { startTime = now; }
    var t = (now - startTime) / 1000;
    if (!hasPointer && !reduce) {
      var off = syntheticOffset(t);
      targetDx = off[0]; targetDy = off[1];
    }
    curDx += (targetDx - curDx) * LERP;
    curDy += (targetDy - curDy) * LERP;
    render(curDx, curDy);
    requestAnimationFrame(loop);
  }

  scene.addEventListener('pointermove', function (e) {
    hasPointer = true;
    root.classList.remove('is-demo');
    var v = vectorToButton(e.clientX, e.clientY);
    targetDx = v[0]; targetDy = v[1];
    if (reduce) { curDx = v[0]; curDy = v[1]; render(curDx, curDy); }
  });
  scene.addEventListener('pointerleave', function () {
    hasPointer = false;
    targetDx = PROX_RADIUS_PX * 2; targetDy = 0;
    if (reduce) { curDx = targetDx; curDy = 0; render(curDx, 0); }
  });
  btn.addEventListener('focus', function () {
    hasPointer = true;
    targetDx = 0; targetDy = 0;
    if (reduce) { curDx = 0; curDy = 0; render(0, 0); }
  });
  btn.addEventListener('blur', function () {
    hasPointer = false;
    targetDx = PROX_RADIUS_PX * 2; targetDy = 0;
    if (reduce) { curDx = targetDx; curDy = 0; render(curDx, 0); }
  });

  if (reduce) {
    curDx = PROX_RADIUS_PX * 2; curDy = 0;
    render(curDx, curDy);
  } else {
    requestAnimationFrame(loop);
  }
})();

// ProximityTiltButton — vanilla 판(run/408/demo/03-btn-proximity-tilt-angle-follow/index.html) 의 React 포트.
// 커서–버튼 중심 방향 벡터를 단위 벡터로 정규화하고, 거리 값(가까울수록 1)을 그 방향의 각도 크기로
// 곱한다 — atan2 로 각도를 구하는 계산 한 겹이 단순 좌표 매핑과 다르다.
import { useEffect, useRef, useState } from "react";
import type { PointerEvent as ReactPointerEvent } from "react";
import styles from "./ProximityTiltButton.module.scss";

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

const PROX_RADIUS_PX = 190;
const TA_MAX_DEG = 12;
const LERP = 0.16;

function clamp(v: number, lo: number, hi: number): number {
  return Math.max(lo, Math.min(hi, v));
}

function syntheticOffset(t: number): [number, number] {
  const ang = t * 1.9;
  const rad = 130 * (1 + Math.cos(t * Math.PI));
  return [Math.cos(ang) * rad, Math.sin(ang) * rad * 0.7];
}

export default function ProximityTiltButton() {
  const sceneRef = useRef<HTMLDivElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);
  const badgeRef = useRef<HTMLParagraphElement | null>(null);
  const targetDxRef = useRef<number>(0) as Box<number>;
  const targetDyRef = useRef<number>(0) as Box<number>;
  const curDxRef = useRef<number>(0) as Box<number>;
  const curDyRef = useRef<number>(0) as Box<number>;
  const hasPointerRef = useRef<boolean>(false) as Box<boolean>;
  const frameRef = useRef<number>(0) as Box<number>;
  const t0Ref = useRef<number>(0) as Box<number>;
  const [demo, setDemo] = useState(true);
  const [reduce, setReduce] = useState(false);

  function render(dx: number, dy: number): void {
    const btn = btnRef.current;
    const badge = badgeRef.current;
    if (!btn || !badge) return;
    const d = Math.hypot(dx, dy);
    const p = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
    const ux = d > 0.001 ? dx / d : 0;
    const uy = d > 0.001 ? dy / d : 0;
    const rotY = ux * p * TA_MAX_DEG;
    const rotX = -uy * p * TA_MAX_DEG;
    const lean = p * 6;
    btn.style.transform = "translate(" + (ux * lean).toFixed(2) + "px," + (uy * lean).toFixed(2) + "px) rotateX(" + rotX.toFixed(2) + "deg) rotateY(" + rotY.toFixed(2) + "deg)";
    // 계산 레이어: 같은 기울기 각도(ux·uy·p) 를 테두리 하이라이트 위치·깊이 그림자에도 전파한다.
    const shadowX = ux * p * 16;
    const shadowY = 6 + uy * p * 12;
    const shadowBlur = 14 + p * 22;
    btn.style.boxShadow = shadowX.toFixed(1) + "px " + shadowY.toFixed(1) + "px " + shadowBlur.toFixed(1) + "px rgba(23,20,26," + (0.2 + p * 0.3).toFixed(2) + ")";
    btn.style.setProperty("--hl-x", (50 + ux * 38).toFixed(1) + "%");
    btn.style.setProperty("--hl-y", (50 + uy * 38).toFixed(1) + "%");
    btn.style.setProperty("--hl-o", (0.12 + p * 0.5).toFixed(2));
    badge.textContent = "각도 값 " + Math.round(rotY) + "°";
  }

  function vectorToButton(x: number, y: number): [number, number] {
    const btn = btnRef.current;
    if (!btn) return [PROX_RADIUS_PX * 2, 0];
    const r = btn.getBoundingClientRect();
    const cx = r.left + r.width / 2;
    const cy = r.top + r.height / 2;
    return [x - cx, y - cy];
  }

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

  useEffect(() => {
    if (reduce) {
      curDxRef.current = PROX_RADIUS_PX * 2;
      curDyRef.current = 0;
      render(curDxRef.current, curDyRef.current);
      return;
    }
    function loop(now: number): void {
      if (t0Ref.current === 0) t0Ref.current = now;
      const t = (now - t0Ref.current) / 1000;
      if (!hasPointerRef.current) {
        const off = syntheticOffset(t);
        targetDxRef.current = off[0];
        targetDyRef.current = off[1];
      }
      curDxRef.current += (targetDxRef.current - curDxRef.current) * LERP;
      curDyRef.current += (targetDyRef.current - curDyRef.current) * LERP;
      render(curDxRef.current, curDyRef.current);
      frameRef.current = requestAnimationFrame(loop);
    }
    frameRef.current = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(frameRef.current);
  }, [reduce]);

  function onPointerMove(event: ReactPointerEvent<HTMLDivElement>): void {
    hasPointerRef.current = true;
    setDemo(false);
    const v = vectorToButton(event.clientX, event.clientY);
    targetDxRef.current = v[0];
    targetDyRef.current = v[1];
    if (reduce) { curDxRef.current = v[0]; curDyRef.current = v[1]; render(curDxRef.current, curDyRef.current); }
  }

  function onPointerLeave(): void {
    hasPointerRef.current = false;
    targetDxRef.current = PROX_RADIUS_PX * 2;
    targetDyRef.current = 0;
    if (reduce) { curDxRef.current = targetDxRef.current; curDyRef.current = 0; render(curDxRef.current, 0); }
  }

  function onFocus(): void {
    hasPointerRef.current = true;
    targetDxRef.current = 0;
    targetDyRef.current = 0;
    if (reduce) { curDxRef.current = 0; curDyRef.current = 0; render(0, 0); }
  }

  function onBlur(): void {
    hasPointerRef.current = false;
    targetDxRef.current = PROX_RADIUS_PX * 2;
    targetDyRef.current = 0;
    if (reduce) { curDxRef.current = targetDxRef.current; curDyRef.current = 0; render(curDxRef.current, 0); }
  }

  const cls = [styles.ta, demo ? styles.isDemo : ""].filter(Boolean).join(" ");
  return (
    <main className={styles.stage}>
      <div className={cls}>
        <p className={styles.badge} ref={badgeRef}>각도 값 0°</p>
        <div className={styles.scene} ref={sceneRef} onPointerMove={onPointerMove} onPointerLeave={onPointerLeave}>
          <button className={styles.btn} ref={btnRef} type="button" onFocus={onFocus} onBlur={onBlur}>
            <span>구매하기</span>
          </button>
        </div>
      </div>
    </main>
  );
}