02Loader an Arrived-particle Count Value Fills

<main class="stage">
<div class="ld" id="ld">
  <p class="ld__hint">
    <svg class="ld__ico" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M232 56v56a8 8 0 0 1-16 0V91.3l-25.6 25.7A80 80 0 1 1 174 60a8 8 0 1 1-9 13.2A64 64 0 1 0 179.7 128H216a8 8 0 0 1 0 16h-56a8 8 0 0 1-8-8V80a8 8 0 0 1 16 0v20.7L192.7 76A80.1 80.1 0 0 0 64 128a8 8 0 0 1-16 0a96 96 0 0 1 163.6-68.3L224 71.3V56a8 8 0 0 1 8 8" opacity=".2"/><path d="M224 48a8 8 0 0 0-8 8v15.3l-11.7-11.6a96 96 0 1 0 27.6 51.6a8 8 0 0 0-15.8 2.5a80 80 0 1 1-23-43l-25.7 25.7A8 8 0 0 0 173 112h56a8 8 0 0 0 8-8V56a8 8 0 0 0-13-8"/></g></svg>
    <span>Click or press the space bar to pause or restart</span>
  </p>
  <div class="ld__field" id="field" role="application" aria-label="Particle swarm convergence test panel" tabindex="0">
    <canvas class="ld__cv" id="cv"></canvas>
    <b class="ld__badge" aria-hidden="true"><span class="ld__badgeNum" id="pct">0%</span><span class="ld__badgeUnit">Converge</span></b>
  </div>
</div>
</main>

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

// 입자 군집 수렴 로더 — 흩어진 입자 중 중심에 도착한 개수/전체 개수가 진행률이다.
// 움직임은 전부 캔버스 rAF 루프 안에 있다. CSS 는 무대·판·배지만 맡는다(@keyframes 0개 — 077 선례와 같은 이유).

$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-lilac;

@include stage($stage-yellow);

.ld {
  --paper: #{$subject-cream};
  --paper-fade: #{rgba($subject-cream, .16)};
  --ink: #{$subject-ink};
  --dot: #{rgba($subject-ink, .38)};
  --core: #{$subject-lilac};
  --line: #{rgba($subject-lilac, .3)};

  display: flex; flex-direction: column; gap: $sp-2;
  width: 100%; max-width: 424px;
}

.ld__hint {
  display: flex; align-items: center; gap: $sp-1; margin: 0;
  font-weight: 700; font-size: clamp(10px, 2.8vw, 12px); line-height: 1.35;
  color: $subject-ink;
}
.ld__ico { width: 16px; height: 16px; flex: 0 0 auto; color: $subject-blue-deep; }

.ld__field {
  position: relative; height: 208px;
  border-radius: $r-card; overflow: hidden;
  background: $subject-cream;
  box-shadow: inset 0 0 0 1px rgba($subject-ink, .16);
  cursor: pointer;
}
.ld__field:focus-visible { outline: 2px solid $subject-blue-deep; outline-offset: 2px; }

.ld__cv { display: block; width: 100%; height: 100%; }

.ld__badge {
  position: absolute; right: $sp-2; top: $sp-2;
  display: flex; align-items: baseline; gap: $sp-1;
  padding: $sp-1 $sp-2; border-radius: $r-pill;
  background: rgba($subject-ink, .78);
  color: $subject-cream; font-weight: 700; font-size: 11px;
}
.ld__badgeNum { font-size: 13px; color: $stage-yellow; }
.ld__badgeUnit { font-weight: 700; }

@media (max-width: 340px) {
  .ld { gap: $sp-1; }
  .ld__field { height: 124px; }
  .ld__badge { font-size: 10px; padding: 0 $sp-1; }
  .ld__badgeNum { font-size: 11px; }
}

// reduce — 루프를 시작하지 않고 진행률 62% 언저리에서 멈춘 한 장만 그린다.
@media (prefers-reduced-motion: reduce) {
  .ld.is-still .ld__field { cursor: default !important; }
  .ld.is-still .ld__badge { opacity: .92 !important; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ld {
  --paper: #fff7e6;
  --paper-fade: rgba(255, 247, 230, 0.16);
  --ink: #17141a;
  --dot: rgba(23, 20, 26, 0.38);
  --core: #b9a0ff;
  --line: rgba(185, 160, 255, 0.3);
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 100%;
  max-width: 424px;
}

.ld__hint {
  display: flex;
  align-items: center;
  gap: 4px;
  margin: 0;
  font-weight: 700;
  font-size: clamp(10px, 2.8vw, 12px);
  line-height: 1.35;
  color: #17141a;
}

.ld__ico {
  width: 16px;
  height: 16px;
  flex: 0 0 auto;
  color: #0a4fe8;
}

.ld__field {
  position: relative;
  height: 208px;
  border-radius: 16px;
  overflow: hidden;
  background: #fff7e6;
  box-shadow: inset 0 0 0 1px rgba(23, 20, 26, 0.16);
  cursor: pointer;
}

.ld__field:focus-visible {
  outline: 2px solid #0a4fe8;
  outline-offset: 2px;
}

.ld__cv {
  display: block;
  width: 100%;
  height: 100%;
}

.ld__badge {
  position: absolute;
  right: 8px;
  top: 8px;
  display: flex;
  align-items: baseline;
  gap: 4px;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.78);
  color: #fff7e6;
  font-weight: 700;
  font-size: 11px;
}

.ld__badgeNum {
  font-size: 13px;
  color: #ffd23f;
}

.ld__badgeUnit {
  font-weight: 700;
}

@media (max-width: 340px) {
  .ld {
    gap: 4px;
  }
  .ld__field {
    height: 124px;
  }
  .ld__badge {
    font-size: 10px;
    padding: 0 4px;
  }
  .ld__badgeNum {
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ld.is-still .ld__field {
    cursor: default !important;
  }
  .ld.is-still .ld__badge {
    opacity: 0.92 !important;
  }
}

// 입자 군집 Converge 로더 — 무작위로 흩어진 입자 중 중심에 도착한 개수를 전체 개수로 나눈 비율이 진행률이다.
// 흩어진 시작 위치·도착 순서는 고정 Seeds LCG 로 정해 항상 같은 그림이 나온다(Math.random 0).
var root = document.getElementById('ld');
var field = document.getElementById('field');
var cv = document.getElementById('cv');
var ctx = cv.getContext('2d');
var pctEl = document.getElementById('pct');

var css = getComputedStyle(root);
var PAPER = css.getPropertyValue('--paper').trim();
var PAPER_FADE = css.getPropertyValue('--paper-fade').trim();
var INK = css.getPropertyValue('--ink').trim();
var DOT = css.getPropertyValue('--dot').trim();
var CORE = css.getPropertyValue('--core').trim();
var LINE = css.getPropertyValue('--line').trim();

function makeRng(seed) {
  var s = seed >>> 0;
  return function () {
    s = (1103515245 * s + 12345) >>> 0;
    return (s >>> 8) / 16777216;
  };
}

var N = 42;
var LOOP = 1.9;
var rng = makeRng(20260923);
var order = [];
for (var oi = 0; oi < N; oi++) order.push(oi);
for (var oj = N - 1; oj > 0; oj--) {           // Fisher-Yates — 도착 순서를 고정 시드로 뒤섞는다
  var ok = Math.floor(rng() * (oj + 1));
  var tmp = order[oj]; order[oj] = order[ok]; order[ok] = tmp;
}
var particles = [];
for (var i = 0; i < N; i++) {
  var ang = rng() * Math.PI * 2;
  var rad = 0.34 + rng() * 0.62;                // 정규화 반지름(0.34~0.96) — 가장자리 쪽에 흩어진다
  particles.push({
    hx: 0.5 + Math.cos(ang) * rad * 0.5,        // 흩어진 자리(정규화 0~1)
    hy: 0.5 + Math.sin(ang) * rad * 0.5,
    px: 0, py: 0,
    rank: order[i],
    jf: 0.6 + rng() * 1.1,                       // 각자 다른 흔들림 진동수
    jp: rng() * Math.PI * 2
  });
}

var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
var W = 0, H = 0, dpr = 1;
var paused = false;
var t0 = 0;
var raf = 0;
var inited = false;

function fit() {
  var r = field.getBoundingClientRect();
  dpr = window.devicePixelRatio || 1;
  W = r.width; H = r.height;
  cv.width = Math.round(W * dpr); cv.height = Math.round(H * dpr);
  ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
  if (!inited) {
    for (var i = 0; i < N; i++) { particles[i].px = particles[i].hx * W; particles[i].py = particles[i].hy * H; }
    inited = true;
  }
}

function draw(sec) {
  // 완전히 지우지 않고 옅은 판 색을 덧칠한다 — 입자가 지나간 자리에 꼬리가 남아
  // 군집이 살아 움직이는 느낌을 준다(궤적 잔상, 매 프레임 픽셀이 크게 바뀐다).
  ctx.fillStyle = PAPER_FADE;
  ctx.fillRect(0, 0, W, H);

  var t = sec % LOOP;
  var p = t / LOOP;                              // 0→1 진행률 — 도착 입자 비율의 목표값
  var arrived = Math.floor(p * N);
  var cx = W * 0.5, cy = H * 0.5;

  for (var i = 0; i < N; i++) {
    var q = particles[i];
    var tx, ty;
    if (q.rank < arrived) {
      var orbit = 5 + 3 * Math.sin(sec * q.jf + q.jp);
      tx = cx + Math.cos(sec * 1.4 + q.jp) * orbit;
      ty = cy + Math.sin(sec * 1.4 + q.jp) * orbit;
    } else {
      tx = q.hx * W + Math.sin(sec * q.jf + q.jp) * 4;
      ty = q.hy * H + Math.cos(sec * q.jf * 0.8 + q.jp) * 4;
    }
    q.px += (tx - q.px) * 0.14;
    q.py += (ty - q.py) * 0.14;
  }

  // 도착한 입자에서 중심으로 옅은 실선
  ctx.strokeStyle = LINE;
  ctx.lineWidth = 1;
  ctx.beginPath();
  for (var j = 0; j < N; j++) {
    var qj = particles[j];
    if (qj.rank < arrived) { ctx.moveTo(qj.px, qj.py); ctx.lineTo(cx, cy); }
  }
  ctx.stroke();

  // 중심 원 — 도착 비율이 밝기·반지름을 함께 키운다
  var frac = arrived / N;
  var coreR = 10 + frac * 22;
  var glow = ctx.createRadialGradient(cx, cy, 0, cx, cy, coreR * 1.8);
  glow.addColorStop(0, CORE);
  glow.addColorStop(1, 'rgba(0,0,0,0)');
  ctx.globalAlpha = 0.35 + frac * 0.5;
  ctx.fillStyle = glow;
  ctx.beginPath();
  ctx.arc(cx, cy, coreR * 1.8, 0, Math.PI * 2);
  ctx.fill();
  ctx.globalAlpha = 1;
  ctx.fillStyle = CORE;
  ctx.beginPath();
  ctx.arc(cx, cy, coreR, 0, Math.PI * 2);
  ctx.fill();

  // 입자
  for (var k = 0; k < N; k++) {
    var qk = particles[k];
    ctx.fillStyle = qk.rank < arrived ? CORE : DOT;
    ctx.beginPath();
    ctx.arc(qk.px, qk.py, qk.rank < arrived ? 4 : 3.2, 0, Math.PI * 2);
    ctx.fill();
  }

  var pct = Math.round(frac * 100);
  pctEl.textContent = pct + '%';
}

function togglePause() {
  paused = !paused;
  root.classList.toggle('is-paused', paused);
}
function restart() {
  t0 = performance.now();
  draw(0);
}

field.addEventListener('click', function () { togglePause(); });
field.addEventListener('keydown', function (e) {
  if (e.key === ' ' || e.key === 'Enter') { e.preventDefault(); togglePause(); }
  else if (e.key === 'r' || e.key === 'R') { e.preventDefault(); restart(); }
});
window.addEventListener('resize', function () {
  fit();
  if (paused || reduce) draw(((performance.now() - t0) / 1000));
});

function frame(now) {
  if (!paused) draw((now - t0) / 1000);
  raf = requestAnimationFrame(frame);
}

t0 = performance.now();
fit();
ctx.fillStyle = PAPER;
ctx.fillRect(0, 0, W, H);
if (reduce) {
  root.classList.add('is-still');
  draw(LOOP * 0.62);
} else {
  raf = requestAnimationFrame(frame);
}

// ParticleSwarm — vanilla 판(run/395/demo/02-canvas-loader-particle-swarm-converge-count/index.html) 의 React 포트.
// 흩어진 입자 중 중심에 도착한 개수/전체 개수가 진행률이다. 시작 위치·도착 순서는 고정 시드 LCG.
import { useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./ParticleSwarm.module.scss";

export type ParticleSwarmProps = {
  duration?: string;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };
type KeyEvt = { key: string; preventDefault(): void };
type Particle = { hx: number; hy: number; px: number; py: number; rank: number; jf: number; jp: number };

const N = 42;
const LOOP = 1.9;
const FIELD_LABEL = "입자 군집 수렴 실험판";

function makeRng(seed: number): () => number {
  let s = seed >>> 0;
  return function () {
    s = (1103515245 * s + 12345) >>> 0;
    return (s >>> 8) / 16777216;
  };
}

function makeParticles(): Particle[] {
  const rng = makeRng(20260923);
  const order: number[] = [];
  for (let i = 0; i < N; i++) order.push(i);
  for (let j = N - 1; j > 0; j--) {
    const k = Math.floor(rng() * (j + 1));
    const tmp = order[j]; order[j] = order[k]; order[k] = tmp;
  }
  const list: Particle[] = [];
  for (let i = 0; i < N; i++) {
    const ang = rng() * Math.PI * 2;
    const rad = 0.34 + rng() * 0.62;
    list.push({
      hx: 0.5 + Math.cos(ang) * rad * 0.5,
      hy: 0.5 + Math.sin(ang) * rad * 0.5,
      px: 0, py: 0,
      rank: order[i],
      jf: 0.6 + rng() * 1.1,
      jp: rng() * Math.PI * 2,
    });
  }
  return list;
}

export default function ParticleSwarm({
  duration = "1.9s",
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#b9a0ff",                           // vanilla $color: $subject-lilac
}: ParticleSwarmProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const fieldRef = useRef<HTMLDivElement | null>(null);
  const cvRef = useRef<HTMLCanvasElement | null>(null);
  const ctxRef = useRef<CanvasRenderingContext2D | null>(null);
  const pctRef = useRef<HTMLSpanElement | null>(null);
  const sizeRef = useRef({ w: 0, h: 0, dpr: 1, inited: false }) as Box<{ w: number; h: number; dpr: number; inited: boolean }>;
  const particlesRef = useRef(makeParticles()) as Box<Particle[]>;
  const pausedRef = useRef(false) as Box<boolean>;
  const t0Ref = useRef(0) as Box<number>;
  const rafRef = useRef(0) as Box<number>;
  const vars: Vars = { "--duration": duration, "--easing": easing, "--color": color };

  function reduced(): boolean {
    return window.matchMedia("(prefers-reduced-motion: reduce)").matches;
  }

  function fit(): void {
    const field = fieldRef.current;
    const cv = cvRef.current;
    if (!field || !cv) return;
    const r = field.getBoundingClientRect();
    const dpr = window.devicePixelRatio || 1;
    const size = sizeRef.current;
    size.w = r.width; size.h = r.height; size.dpr = dpr;
    cv.width = Math.round(r.width * dpr);
    cv.height = Math.round(r.height * dpr);
    const ctx = ctxRef.current;
    if (ctx) ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    if (!size.inited) {
      const list = particlesRef.current;
      for (let i = 0; i < N; i++) { list[i].px = list[i].hx * r.width; list[i].py = list[i].hy * r.height; }
      size.inited = true;
    }
  }

  function draw(sec: number): void {
    const ctx = ctxRef.current;
    const root = rootRef.current;
    if (!ctx || !root) return;
    const W = sizeRef.current.w, H = sizeRef.current.h;
    const cssv = (n: string) => getComputedStyle(root).getPropertyValue(n).trim();
    const PAPER_FADE = cssv("--paper-fade"), DOT = cssv("--dot"), CORE = cssv("--core"), LINE = cssv("--line");

    // 완전히 지우지 않고 옅은 판 색을 덧칠한다 — 입자 궤적 잔상이 남는다
    ctx.fillStyle = PAPER_FADE;
    ctx.fillRect(0, 0, W, H);

    const t = sec % LOOP;
    const p = t / LOOP;
    const arrived = Math.floor(p * N);
    const cx = W * 0.5, cy = H * 0.5;
    const list = particlesRef.current;

    for (let i = 0; i < N; i++) {
      const q = list[i];
      let tx: number, ty: number;
      if (q.rank < arrived) {
        const orbit = 5 + 3 * Math.sin(sec * q.jf + q.jp);
        tx = cx + Math.cos(sec * 1.4 + q.jp) * orbit;
        ty = cy + Math.sin(sec * 1.4 + q.jp) * orbit;
      } else {
        tx = q.hx * W + Math.sin(sec * q.jf + q.jp) * 4;
        ty = q.hy * H + Math.cos(sec * q.jf * 0.8 + q.jp) * 4;
      }
      q.px += (tx - q.px) * 0.14;
      q.py += (ty - q.py) * 0.14;
    }

    ctx.strokeStyle = LINE;
    ctx.lineWidth = 1;
    ctx.beginPath();
    for (let j = 0; j < N; j++) {
      const qj = list[j];
      if (qj.rank < arrived) { ctx.moveTo(qj.px, qj.py); ctx.lineTo(cx, cy); }
    }
    ctx.stroke();

    const frac = arrived / N;
    const coreR = 10 + frac * 22;
    const glow = ctx.createRadialGradient(cx, cy, 0, cx, cy, coreR * 1.8);
    glow.addColorStop(0, CORE);
    glow.addColorStop(1, "rgba(0,0,0,0)");
    ctx.globalAlpha = 0.35 + frac * 0.5;
    ctx.fillStyle = glow;
    ctx.beginPath();
    ctx.arc(cx, cy, coreR * 1.8, 0, Math.PI * 2);
    ctx.fill();
    ctx.globalAlpha = 1;
    ctx.fillStyle = CORE;
    ctx.beginPath();
    ctx.arc(cx, cy, coreR, 0, Math.PI * 2);
    ctx.fill();

    for (let k = 0; k < N; k++) {
      const qk = list[k];
      ctx.fillStyle = qk.rank < arrived ? CORE : DOT;
      ctx.beginPath();
      ctx.arc(qk.px, qk.py, qk.rank < arrived ? 4 : 3.2, 0, Math.PI * 2);
      ctx.fill();
    }

    const pct = Math.round(frac * 100);
    if (pctRef.current) pctRef.current.textContent = pct + "%";
  }

  function togglePause(): void {
    pausedRef.current = !pausedRef.current;
    const root = rootRef.current;
    if (root) root.classList.toggle("is-paused", pausedRef.current);
  }

  function restart(): void {
    t0Ref.current = performance.now();
    draw(0);
  }

  function onKey(e: KeyEvt): void {
    if (e.key === " " || e.key === "Enter") { e.preventDefault(); togglePause(); }
    else if (e.key === "r" || e.key === "R") { e.preventDefault(); restart(); }
  }

  function onClick(): void {
    togglePause();
  }

  function onResize(): void {
    fit();
    if (pausedRef.current || reduced()) draw((performance.now() - t0Ref.current) / 1000);
  }

  function frame(now: number): void {
    if (!pausedRef.current) draw((now - t0Ref.current) / 1000);
    rafRef.current = requestAnimationFrame(frame);
  }

  useEffect(() => {
    const cv = cvRef.current;
    if (!cv) return;
    ctxRef.current = cv.getContext("2d");
    if (!ctxRef.current) return;
    t0Ref.current = performance.now();
    fit();
    const root0 = rootRef.current;
    if (root0) {
      const paper = getComputedStyle(root0).getPropertyValue("--paper").trim();
      ctxRef.current.fillStyle = paper;
      ctxRef.current.fillRect(0, 0, sizeRef.current.w, sizeRef.current.h);
    }
    window.addEventListener("resize", onResize);
    if (reduced()) {
      const root = rootRef.current;
      if (root) root.classList.add("is-still");
      draw(LOOP * 0.62);
    } else {
      rafRef.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.root} ref={rootRef} style={vars}>
        <p className={styles.hint}>
          <svg className={styles.ico} viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M232 56v56a8 8 0 0 1-16 0V91.3l-25.6 25.7A80 80 0 1 1 174 60a8 8 0 1 1-9 13.2A64 64 0 1 0 179.7 128H216a8 8 0 0 1 0 16h-56a8 8 0 0 1-8-8V80a8 8 0 0 1 16 0v20.7L192.7 76A80.1 80.1 0 0 0 64 128a8 8 0 0 1-16 0a96 96 0 0 1 163.6-68.3L224 71.3V56a8 8 0 0 1 8 8" opacity=".2"/><path d="M224 48a8 8 0 0 0-8 8v15.3l-11.7-11.6a96 96 0 1 0 27.6 51.6a8 8 0 0 0-15.8 2.5a80 80 0 1 1-23-43l-25.7 25.7A8 8 0 0 0 173 112h56a8 8 0 0 0 8-8V56a8 8 0 0 0-13-8"/></g></svg>
          <span>클릭하거나 스페이스바를 누르면 멈추거나 다시 갑니다</span>
        </p>
        <div
          className={styles.field}
          ref={fieldRef}
          role="application"
          aria-label={FIELD_LABEL}
          tabIndex={0}
          onClick={onClick}
          onKeyDown={onKey}
        >
          <canvas className={styles.cv} ref={cvRef}></canvas>
          <b className={styles.badge} aria-hidden="true"><span className={styles.badgeNum} ref={pctRef}>0%</span><span className={styles.badgeUnit}>수렴</span></b>
        </div>
      </div>
    </main>
  );
}