05궤도 반경 값이 좁히는 자기장 로더

<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>클릭하거나 스페이스바를 누르면 멈추거나 다시 갑니다</span>
  </p>
  <div class="ld__field" id="field" role="application" aria-label="자기장 궤도 흡인 실험판" 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">흡인</span></b>
  </div>
</div>
</main>

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

// 자기장 로더 — 입자 10개가 코어를 돌며 궤도 반지름이 진행률에 비례해 0 에 가까워진다(훅 고정).
// 움직임은 전부 캔버스 rAF 루프 안에 있다. CSS 는 무대·판·배지만 맡는다(@keyframes 0개 — 077 선례와 같은 이유).

$duration: $dur-loop;
$easing: $ease-pop;
$color: $subject-blue-light;

@include stage($stage-ink);

.ld {
  --paper: #{$subject-ink};
  --paper-fade: #{rgba($subject-ink, .12)};
  --core: #{$subject-cream};
  --line: #{rgba($subject-cream, .28)};
  --p1: #{$subject-blue-light};
  --p2: #{$subject-mint};
  --p3: #{$subject-pink};

  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-cream;
}
.ld__ico { width: 16px; height: 16px; flex: 0 0 auto; color: $subject-blue-light; }

.ld__field {
  position: relative; height: 208px;
  border-radius: $r-card; overflow: hidden;
  background: $subject-ink;
  box-shadow: inset 0 0 0 1px rgba($subject-cream, .16);
  cursor: pointer;
}
.ld__field:focus-visible { outline: 2px solid $subject-blue-light; 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-cream, .18);
  box-shadow: inset 0 0 0 1px rgba($subject-cream, .3);
  color: $subject-cream; font-weight: 700; font-size: 11px;
}
.ld__badgeNum { font-size: 13px; color: $subject-blue-light; }
.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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ld {
  --paper: #17141a;
  --paper-fade: rgba(23, 20, 26, 0.12);
  --core: #fff7e6;
  --line: rgba(255, 247, 230, 0.28);
  --p1: #5b8cf8;
  --p2: #4cd4a6;
  --p3: #ff9ebb;
  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: #fff7e6;
}

.ld__ico {
  width: 16px;
  height: 16px;
  flex: 0 0 auto;
  color: #5b8cf8;
}

.ld__field {
  position: relative;
  height: 208px;
  border-radius: 16px;
  overflow: hidden;
  background: #17141a;
  box-shadow: inset 0 0 0 1px rgba(255, 247, 230, 0.16);
  cursor: pointer;
}

.ld__field:focus-visible {
  outline: 2px solid #5b8cf8;
  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(255, 247, 230, 0.18);
  box-shadow: inset 0 0 0 1px rgba(255, 247, 230, 0.3);
  color: #fff7e6;
  font-weight: 700;
  font-size: 11px;
}

.ld__badgeNum {
  font-size: 13px;
  color: #5b8cf8;
}

.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;
  }
}

// 자기장 로더 — 입자 여러 개가 코어를 돈다. 궤도 반지름은 진행률에 비례해 줄어들고
// 진행률이 1 에 닿는 순간 반지름이 정확히 0(코어에 흡수)이 되었다가 다음 루프에서 다시 퍼진다.
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 CORE = css.getPropertyValue('--core').trim();
var LINE = css.getPropertyValue('--line').trim();
var P1 = css.getPropertyValue('--p1').trim();
var P2 = css.getPropertyValue('--p2').trim();
var P3 = css.getPropertyValue('--p3').trim();
var PALETTE = [P1, P2, P3];

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

var N = 10;
var LOOP = 2.4;
var rng = makeRng(20260925);
var parts = [];
for (var i = 0; i < N; i++) {
  parts.push({
    r0: 0.42 + rng() * 0.56,               // 궤도 반지름 비율(필드 반지름 대비) — 흡인 시작점
    phase: rng() * Math.PI * 2,
    speed: (0.55 + rng() * 0.9) * (rng() < 0.5 ? -1 : 1)
  });
}

var W = 0, H = 0, dpr = 1, cxp = 0, cyp = 0, fieldR = 0;

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);
  cxp = W * 0.5; cyp = H * 0.5;
  fieldR = Math.min(W, H) * 0.44;
  ctx.fillStyle = PAPER;
  ctx.fillRect(0, 0, W, H);
}

function draw(sec) {
  var t = sec % LOOP;
  var p = t / LOOP;                       // 0→1 진행률
  var shrink = 1 - p;                     // 궤도 반지름 배율 — p=1 에서 정확히 0(흡인 완료)

  ctx.fillStyle = PAPER_FADE;
  ctx.fillRect(0, 0, W, H);

  ctx.strokeStyle = LINE;
  ctx.lineWidth = 1.6;
  for (var i = 0; i < N; i++) {
    var q = parts[i];
    var rad = fieldR * q.r0 * shrink;
    var ang = q.phase + sec * q.speed;
    var x = cxp + Math.cos(ang) * rad;
    var y = cyp + Math.sin(ang) * rad;
    ctx.beginPath();
    ctx.moveTo(cxp, cyp);
    ctx.lineTo(x, y);
    ctx.stroke();
    ctx.fillStyle = PALETTE[i % PALETTE.length];
    ctx.beginPath();
    ctx.arc(x, y, 6.2, 0, Math.PI * 2);
    ctx.fill();
  }

  var coreR = 8 + (1 - shrink) * 14;      // 흡인이 진행될수록 코어가 커진다(자기장이 강해지는 느낌)
  var grad = ctx.createRadialGradient(cxp, cyp, 0, cxp, cyp, coreR * 2.2);
  grad.addColorStop(0, CORE);
  grad.addColorStop(1, 'rgba(0,0,0,0)');
  ctx.fillStyle = grad;
  ctx.beginPath();
  ctx.arc(cxp, cyp, coreR * 2.2, 0, Math.PI * 2);
  ctx.fill();
  ctx.fillStyle = CORE;
  ctx.beginPath();
  ctx.arc(cxp, cyp, coreR, 0, Math.PI * 2);
  ctx.fill();

  pctEl.textContent = Math.round(p * 100) + '%';
}

var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
var paused = false;
var t0 = 0;
var raf = 0;

function togglePause() {
  paused = !paused;
  root.classList.toggle('is-paused', paused);
}
function restart() {
  t0 = performance.now();
  fit();
  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();
if (reduce) {
  root.classList.add('is-still');
  draw(LOOP * 0.62);
} else {
  raf = requestAnimationFrame(frame);
}

// MagneticOrbit — vanilla 판(run/395/demo/05-canvas-loader-magnetic-field-pull-orbit/index.html) 의 React 포트.
// 입자 10개가 코어를 돌며 궤도 반지름이 진행률에 비례해 0 에 가까워진다(훅 고정 — magnetic-field-pull-orbit).
import { useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./MagneticOrbit.module.scss";

export type MagneticOrbitProps = {
  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 = { r0: number; phase: number; speed: number };

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

const N = 10;
const LOOP = 2.4;
const FIELD_LABEL = "자기장 궤도 흡인 실험판";

function makeParticles(): Particle[] {
  const rng = makeRng(20260925);
  const list: Particle[] = [];
  for (let i = 0; i < N; i++) {
    list.push({
      r0: 0.42 + rng() * 0.56,
      phase: rng() * Math.PI * 2,
      speed: (0.55 + rng() * 0.9) * (rng() < 0.5 ? -1 : 1),
    });
  }
  return list;
}

export default function MagneticOrbit({
  duration = "2.4s",
  easing = "cubic-bezier(.2, 1.4, .4, 1)",   // vanilla $easing: $ease-pop
  color = "#5b8cf8",                          // vanilla $color: $subject-blue-light
}: MagneticOrbitProps) {
  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, cx: 0, cy: 0, fieldR: 0 }) as Box<{ w: number; h: number; dpr: number; cx: number; cy: number; fieldR: number }>;
  const partsRef = useRef<Particle[]>(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;
    const ctx = ctxRef.current;
    if (!field || !cv || !ctx) 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);
    ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    size.cx = r.width * 0.5; size.cy = r.height * 0.5;
    size.fieldR = Math.min(r.width, r.height) * 0.44;
    const root = rootRef.current;
    if (root) {
      const paper = getComputedStyle(root).getPropertyValue("--paper").trim();
      ctx.fillStyle = paper;
      ctx.fillRect(0, 0, r.width, r.height);
    }
  }

  function draw(sec: number): void {
    const ctx = ctxRef.current;
    const root = rootRef.current;
    if (!ctx || !root) return;
    const size = sizeRef.current;
    const W = size.w, H = size.h;
    const t = sec % LOOP;
    const p = t / LOOP;
    const shrink = 1 - p;

    const cssv = (n: string) => getComputedStyle(root).getPropertyValue(n).trim();
    const PAPER_FADE = cssv("--paper-fade"), CORE = cssv("--core"), LINE = cssv("--line");
    const PALETTE = [cssv("--p1"), cssv("--p2"), cssv("--p3")];

    ctx.fillStyle = PAPER_FADE;
    ctx.fillRect(0, 0, W, H);

    ctx.strokeStyle = LINE;
    ctx.lineWidth = 1.6;
    const parts = partsRef.current;
    for (let i = 0; i < N; i++) {
      const q = parts[i];
      const rad = size.fieldR * q.r0 * shrink;
      const ang = q.phase + sec * q.speed;
      const x = size.cx + Math.cos(ang) * rad;
      const y = size.cy + Math.sin(ang) * rad;
      ctx.beginPath();
      ctx.moveTo(size.cx, size.cy);
      ctx.lineTo(x, y);
      ctx.stroke();
      ctx.fillStyle = PALETTE[i % PALETTE.length];
      ctx.beginPath();
      ctx.arc(x, y, 6.2, 0, Math.PI * 2);
      ctx.fill();
    }

    const coreR = 8 + (1 - shrink) * 14;
    const grad = ctx.createRadialGradient(size.cx, size.cy, 0, size.cx, size.cy, coreR * 2.2);
    grad.addColorStop(0, CORE);
    grad.addColorStop(1, "rgba(0,0,0,0)");
    ctx.fillStyle = grad;
    ctx.beginPath();
    ctx.arc(size.cx, size.cy, coreR * 2.2, 0, Math.PI * 2);
    ctx.fill();
    ctx.fillStyle = CORE;
    ctx.beginPath();
    ctx.arc(size.cx, size.cy, coreR, 0, Math.PI * 2);
    ctx.fill();

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

  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();
    fit();
    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();
    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}>흡인</span></b>
        </div>
      </div>
    </main>
  );
}