09거리 값만큼 입자가 모여드는 버튼

<main class="stage">
<div class="pd is-demo" id="pd">
  <p class="pd__badge" id="pdBadge">입자 값 0/6</p>
  <div class="pd__scene" id="pdScene">
    <div class="pd__wrap" id="pdWrap">
      <canvas class="pd__canvas" id="pdCanvas" width="280" height="150" aria-hidden="true"></canvas>
      <button class="pd__btn" id="pdBtn" type="button">가입하기</button>
    </div>
  </div>
</div>
</main>

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

// 핵심: 거리 값이 줄어드는 동안 캔버스에 그리는 입자 개수 값(count)과 궤도 반경(density) 값이
// 함께 바뀐다. 입자마다 고정된 노이즈 오프셋(각도·주기 지터)을 심어 기계적으로 안 보이게 한다.

$duration: $dur-loop;
$easing: linear;
$color: $subject-blue-deep;

@include stage($stage-ink);

.pd {
  display: grid;
  gap: $sp-2;
  justify-items: center;
}

.pd__badge {
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 247, 230, .1);
  color: $subject-cream;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.pd__scene {
  padding: $sp-3;
}

.pd__wrap {
  position: relative;
  width: 340px;
  height: 182px;
  display: grid;
  place-items: center;
  --sw-p: 0;
}

.pd__wrap::before {
  content: '';
  position: absolute;
  inset: -8px;
  border-radius: $r-control;
  background: radial-gradient(circle, rgba($subject-blue-deep, .5), transparent 60%);
  transform: scale(calc(0.65 + var(--sw-p) * 0.35));
  opacity: calc(var(--sw-p) * 0.4);
  pointer-events: none;
  z-index: 0;
}

.pd__canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
}

.pd__btn {
  position: relative;
  border: 0;
  cursor: pointer;
  padding: $sp-4 $sp-8;
  border-radius: $r-control;
  background: $color;
  color: $subject-cream;
  font-size: 16px;
  font-weight: 700;
}

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

@media (max-width: 340px) {
  .pd__scene { padding: $sp-2; }
  .pd__wrap { width: 100%; height: 112px; }
  .pd__btn { padding: $sp-3 $sp-6; font-size: 14px; }
}

@media (prefers-reduced-motion: reduce) {
  .pd__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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.pd {
  display: grid;
  gap: 8px;
  justify-items: center;
}

.pd__badge {
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.1);
  color: #fff7e6;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
}

.pd__scene {
  padding: 12px;
}

.pd__wrap {
  position: relative;
  width: 340px;
  height: 182px;
  display: grid;
  place-items: center;
  --sw-p: 0;
}

.pd__wrap::before {
  content: "";
  position: absolute;
  inset: -8px;
  border-radius: 12px;
  background: radial-gradient(circle, rgba(10, 79, 232, 0.5), transparent 60%);
  transform: scale(calc(0.65 + var(--sw-p) * 0.35));
  opacity: calc(var(--sw-p) * 0.4);
  pointer-events: none;
  z-index: 0;
}

.pd__canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
}

.pd__btn {
  position: relative;
  border: 0;
  cursor: pointer;
  padding: 16px 32px;
  border-radius: 12px;
  background: #0a4fe8;
  color: #fff7e6;
  font-size: 16px;
  font-weight: 700;
}

.pd__btn:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 3px;
}

@media (max-width: 340px) {
  .pd__scene {
    padding: 8px;
  }
  .pd__wrap {
    width: 100%;
    height: 112px;
  }
  .pd__btn {
    padding: 12px 24px;
    font-size: 14px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .pd__btn {
    transition: none;
  }
}

(function () {
  // PROX_PARTICLE_MAX_COUNT — 변형 3: 6 → 14 로 늘리면 입자가 촘촘히 모여 붐비듯 화려해진다.
  var PROX_PARTICLE_MAX_COUNT = 6;
  var PROX_RADIUS_PX = 170;
  var LERP = 0.16;
  var RADIUS_FAR_PX = 92;
  var RADIUS_NEAR_PX = 46;

  var root = document.getElementById('pd');
  var scene = document.getElementById('pdScene');
  var wrap = document.getElementById('pdWrap');
  var btn = document.getElementById('pdBtn');
  var canvas = document.getElementById('pdCanvas');
  var badge = document.getElementById('pdBadge');
  var ctx = canvas.getContext('2d');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

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

  // 캔버스 표시 크기 = 스테이지가 실제로 내준 크기(getBoundingClientRect) — 고정 px 캡을 두지 않는다.
  var radiusScale = 1;
  function resizeCanvas() {
    var r = wrap.getBoundingClientRect();
    var w = Math.max(1, Math.round(r.width));
    var h = Math.max(1, Math.round(r.height));
    if (canvas.width !== w) { canvas.width = w; }
    if (canvas.height !== h) { canvas.height = h; }
    radiusScale = Math.min(w / 280, h / 150);
  }
  resizeCanvas();
  window.addEventListener('resize', resizeCanvas);

  // 입자마다 글자별 노이즈 오프셋과 같은 계열 — 각도·주기에 고정 지터를 심어 기계적으로 안 보이게 한다
  var particles = [];
  for (var i = 0; i < PROX_PARTICLE_MAX_COUNT; i += 1) {
    particles.push({
      baseAngle: (i / PROX_PARTICLE_MAX_COUNT) * Math.PI * 2,
      noise: ((i * 137) % 23) / 23 - 0.5,
      phase: (i * 71) % 100 / 100 * Math.PI * 2,
      size: 2.4 + ((i * 53) % 7) / 7 * 1.6
    });
  }

  var targetP = 0;
  var curP = 0;
  var hasPointer = false;
  var TRAIL_STEPS = 7;
  var trailHistory = [];

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

  function draw(p, t) {
    var w = canvas.width, h = canvas.height;
    ctx.clearRect(0, 0, w, h);
    var cx = w / 2, cy = h / 2;
    var count = p * PROX_PARTICLE_MAX_COUNT;
    var radius = (RADIUS_FAR_PX + (RADIUS_NEAR_PX - RADIUS_FAR_PX) * p) * radiusScale;
    var positions = [];
    particles.forEach(function (pt, i) {
      var visible = clamp(count - i, 0, 1);
      if (visible <= 0) { return; }
      var ang = pt.baseAngle + t * 0.5 + pt.noise * Math.sin(t * 1.3 + pt.phase) * 0.6;
      var rad = radius + pt.noise * 10 * radiusScale * Math.sin(t * 0.9 + pt.phase);
      var x = cx + Math.cos(ang) * rad;
      var y = cy + Math.sin(ang) * rad * 0.72;
      positions.push({ x: x, y: y, size: pt.size * radiusScale * 1.3, alpha: (0.4 + p * 0.6) * visible });
    });
    // 계산 레이어: 최근 몇 프레임의 입자 위치를 옅은 잔상으로 같이 그려 궤적이 남게 한다(전체 캔버스를 덮지 않는다).
    trailHistory.push(positions);
    if (trailHistory.length > TRAIL_STEPS) { trailHistory.shift(); }
    trailHistory.forEach(function (frame, hi) {
      var age = trailHistory.length - hi;
      var fade = 1 - age / (TRAIL_STEPS + 1);
      frame.forEach(function (pos) {
        ctx.globalAlpha = pos.alpha * fade;
        ctx.beginPath();
        ctx.arc(pos.x, pos.y, pos.size * (0.8 + fade * 0.9), 0, Math.PI * 2);
        ctx.fillStyle = '#0a4fe8';
        ctx.fill();
      });
    });
    positions.forEach(function (pos) {
      ctx.globalAlpha = pos.alpha;
      ctx.beginPath();
      ctx.arc(pos.x, pos.y, pos.size, 0, Math.PI * 2);
      ctx.fillStyle = '#fff7e6';
      ctx.fill();
    });
    ctx.globalAlpha = 1;
    // 계산 레이어: 같은 진행률(p)을 입자 뒤 글로우 크기·불투명도에도 전파한다 — 배경과 겹치지 않는 색.
    wrap.style.setProperty('--sw-p', p.toFixed(3));
    badge.textContent = '입자 값 ' + Math.round(count) + '/' + PROX_PARTICLE_MAX_COUNT;
  }

  function syntheticOffset(t) {
    var ang = t * 1.5;
    var rad = 110 * (1 + Math.cos(t * Math.PI));
    return [Math.cos(ang) * rad, Math.sin(ang) * rad];
  }

  var startTime = null;
  function loop(now) {
    if (startTime === null) { startTime = now; }
    var t = (now - startTime) / 1000;
    if (!hasPointer && !reduce) {
      var off = syntheticOffset(t);
      var d = Math.hypot(off[0], off[1]);
      targetP = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
    }
    curP += (targetP - curP) * LERP;
    draw(curP, t);
    requestAnimationFrame(loop);
  }

  scene.addEventListener('pointermove', function (e) {
    hasPointer = true;
    root.classList.remove('is-demo');
    var d = distanceToButton(e.clientX, e.clientY);
    targetP = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
    if (reduce) { curP = targetP; draw(curP, 0); }
  });
  scene.addEventListener('pointerleave', function () {
    hasPointer = false;
    targetP = 0;
    if (reduce) { curP = 0; draw(0, 0); }
  });
  btn.addEventListener('focus', function () {
    hasPointer = true;
    targetP = 1;
    if (reduce) { curP = 1; draw(1, 0); }
  });
  btn.addEventListener('blur', function () {
    hasPointer = false;
    targetP = 0;
    if (reduce) { curP = 0; draw(0, 0); }
  });

  if (reduce) {
    draw(0, 0);
  } else {
    requestAnimationFrame(loop);
  }
})();

// ProximityParticleSwarmButton — vanilla 판(run/408/demo/09-btn-proximity-particle-density-swarm/index.html) 의 React 포트.
// 거리 값이 줄어드는 동안 캔버스에 그리는 입자 개수 값(count)과 궤도 반경(radius) 값이 함께
// 바뀐다. 입자마다 고정된 노이즈 오프셋(각도·주기 지터)을 심어 기계적으로 안 보이게 한다.
import { useEffect, useRef, useState } from "react";
import type { PointerEvent as ReactPointerEvent } from "react";
import styles from "./ProximityParticleSwarmButton.module.scss";

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

type Particle = {
  baseAngle: number;
  noise: number;
  phase: number;
  size: number;
};

type TrailPoint = {
  x: number;
  y: number;
  size: number;
  alpha: number;
};

// PROX_PARTICLE_MAX_COUNT — 변형 3: 6 → 14 로 늘리면 입자가 촘촘히 모여 붐비듯 화려해진다.
const PROX_PARTICLE_MAX_COUNT = 6;
const PROX_RADIUS_PX = 170;
const LERP = 0.16;
const RADIUS_FAR_PX = 92;
const RADIUS_NEAR_PX = 46;
const TRAIL_STEPS = 7;

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

function makeParticles(): Particle[] {
  const list: Particle[] = [];
  for (let i = 0; i < PROX_PARTICLE_MAX_COUNT; i += 1) {
    list.push({
      baseAngle: (i / PROX_PARTICLE_MAX_COUNT) * Math.PI * 2,
      noise: ((i * 137) % 23) / 23 - 0.5,
      phase: ((i * 71) % 100) / 100 * Math.PI * 2,
      size: 2.4 + ((i * 53) % 7) / 7 * 1.6,
    });
  }
  return list;
}

function syntheticOffset(t: number): [number, number] {
  const ang = t * 1.5;
  const rad = 110 * (1 + Math.cos(t * Math.PI));
  return [Math.cos(ang) * rad, Math.sin(ang) * rad];
}

export default function ProximityParticleSwarmButton() {
  const sceneRef = useRef<HTMLDivElement | null>(null);
  const wrapRef = useRef<HTMLDivElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);
  const canvasRef = useRef<HTMLCanvasElement | null>(null);
  const badgeRef = useRef<HTMLParagraphElement | null>(null);
  const particlesRef = useRef<Particle[]>(makeParticles()) as Box<Particle[]>;
  const targetPRef = useRef<number>(0) as Box<number>;
  const curPRef = 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 radiusScaleRef = useRef<number>(1) as Box<number>;
  const trailHistoryRef = useRef<TrailPoint[][]>([]) as Box<TrailPoint[][]>;
  const [demo, setDemo] = useState(true);
  const [reduce, setReduce] = useState(false);

  function resizeCanvas(): void {
    const wrap = wrapRef.current;
    const canvas = canvasRef.current;
    if (!wrap || !canvas) return;
    const r = wrap.getBoundingClientRect();
    const w = Math.max(1, Math.round(r.width));
    const h = Math.max(1, Math.round(r.height));
    if (canvas.width !== w) canvas.width = w;
    if (canvas.height !== h) canvas.height = h;
    radiusScaleRef.current = Math.min(w / 280, h / 150);
  }

  function draw(p: number, t: number): void {
    const canvas = canvasRef.current;
    const badge = badgeRef.current;
    const wrap = wrapRef.current;
    if (!canvas || !badge || !wrap) return;
    const ctx = canvas.getContext("2d");
    if (!ctx) return;
    const w = canvas.width;
    const h = canvas.height;
    ctx.clearRect(0, 0, w, h);
    const cx = w / 2;
    const cy = h / 2;
    const radiusScale = radiusScaleRef.current;
    const count = p * PROX_PARTICLE_MAX_COUNT;
    const radius = (RADIUS_FAR_PX + (RADIUS_NEAR_PX - RADIUS_FAR_PX) * p) * radiusScale;
    const positions: TrailPoint[] = [];
    particlesRef.current.forEach((pt, i) => {
      const visible = clamp(count - i, 0, 1);
      if (visible <= 0) return;
      const ang = pt.baseAngle + t * 0.5 + pt.noise * Math.sin(t * 1.3 + pt.phase) * 0.6;
      const rad = radius + pt.noise * 10 * radiusScale * Math.sin(t * 0.9 + pt.phase);
      const x = cx + Math.cos(ang) * rad;
      const y = cy + Math.sin(ang) * rad * 0.72;
      positions.push({ x, y, size: pt.size * radiusScale, alpha: (0.4 + p * 0.6) * visible });
    });
    // 계산 레이어: 최근 몇 프레임의 입자 위치를 옅은 잔상으로 같이 그려 궤적이 남게 한다(전체 캔버스를 덮지 않는다).
    const trailHistory = trailHistoryRef.current;
    trailHistory.push(positions);
    if (trailHistory.length > TRAIL_STEPS) trailHistory.shift();
    trailHistory.forEach((frame, hi) => {
      const age = trailHistory.length - hi;
      const fade = 1 - age / (TRAIL_STEPS + 1);
      frame.forEach((pos) => {
        ctx.globalAlpha = pos.alpha * fade;
        ctx.beginPath();
        ctx.arc(pos.x, pos.y, pos.size * (0.8 + fade * 0.9), 0, Math.PI * 2);
        ctx.fillStyle = "#0a4fe8";
        ctx.fill();
      });
    });
    positions.forEach((pos) => {
      ctx.globalAlpha = pos.alpha;
      ctx.beginPath();
      ctx.arc(pos.x, pos.y, pos.size, 0, Math.PI * 2);
      ctx.fillStyle = "#fff7e6";
      ctx.fill();
    });
    ctx.globalAlpha = 1;
    // 계산 레이어: 같은 진행률(p)을 입자 뒤 글로우 크기·불투명도에도 전파한다 — 배경과 겹치지 않는 색.
    wrap.style.setProperty("--sw-p", p.toFixed(3));
    badge.textContent = "입자 값 " + Math.round(count) + "/" + PROX_PARTICLE_MAX_COUNT;
  }

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

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

  useEffect(() => {
    resizeCanvas();
    window.addEventListener("resize", resizeCanvas);
    return () => window.removeEventListener("resize", resizeCanvas);
  }, []);

  useEffect(() => {
    if (reduce) {
      draw(0, 0);
      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);
        const d = Math.hypot(off[0], off[1]);
        targetPRef.current = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
      }
      curPRef.current += (targetPRef.current - curPRef.current) * LERP;
      draw(curPRef.current, t);
      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 d = distanceToButton(event.clientX, event.clientY);
    targetPRef.current = clamp(1 - d / PROX_RADIUS_PX, 0, 1);
    if (reduce) { curPRef.current = targetPRef.current; draw(curPRef.current, 0); }
  }

  function onPointerLeave(): void {
    hasPointerRef.current = false;
    targetPRef.current = 0;
    if (reduce) { curPRef.current = 0; draw(0, 0); }
  }

  function onFocus(): void {
    hasPointerRef.current = true;
    targetPRef.current = 1;
    if (reduce) { curPRef.current = 1; draw(1, 0); }
  }

  function onBlur(): void {
    hasPointerRef.current = false;
    targetPRef.current = 0;
    if (reduce) { curPRef.current = 0; draw(0, 0); }
  }

  const cls = [styles.pd, demo ? styles.isDemo : ""].filter(Boolean).join(" ");
  return (
    <main className={styles.stage}>
      <div className={cls}>
        <p className={styles.badge} ref={badgeRef}>입자 값 0/6</p>
        <div className={styles.scene} ref={sceneRef} onPointerMove={onPointerMove} onPointerLeave={onPointerLeave}>
          <div className={styles.wrap} ref={wrapRef}>
            <canvas className={styles.canvas} ref={canvasRef} width={280} height={150} aria-hidden="true" />
            <button className={styles.btn} ref={btnRef} type="button" onFocus={onFocus} onBlur={onBlur}>가입하기</button>
          </div>
        </div>
      </div>
    </main>
  );
}