06Tidal tail close-up — the fling seen through one star's trail
Leave a trail on just one star among thousands and the moment of the fling appears — an individual orbit shuttling between the two galactic centers, losing energy, thrown outward. The tail explained as one star's story, not a statistic.
Best forData storytelling, highlight animations
CanvasRenderingContext2DlineTorequestAnimationFrame
<main class="stage">
<div class="gx is-demo" id="gxRoot">
<p class="gx__hint">
<span>Trail just one star among thousands: the moment the tail forms, it shuttles between the two cores and is flung out</span>
</p>
<div class="gx__field" id="gxField" role="application" aria-label="Tidal tail close-up lab" tabindex="0">
<canvas class="gx__cv" id="gxCv"></canvas>
</div>
<div class="gx__bar">
<span class="gx__meta">340 stars · one tracked orbit</span>
<span class="gx__meta gx__meta--dim">canvas · one-star trail · requestAnimationFrame</span>
</div>
</div>
</main>@use "../../../../site/static/demo-tokens" as *;
// 조석 꼬리 클로즈업(06). 한 별만 굵은 궤적으로 추적하는 장면 —
// 나선 팔 형성(02). @keyframes 를 두지 않는다 —
// 움직임은 전부 캔버스 rAF 루프(중심 질량 + 별 상호 중력 O(N²) 레인포드 적분 → 점 그리기)가 만든다.
// 무대는 편 공통 심우주 팔레트. 파스텔 주색을 --gx-* 로 편 전체(01~09) 공통 규격.
$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-lilac;
// ── 편 공통 심우주 팔레트(BD9~11 원칙: 편마다 다시 정하지 않는다) ──
$gx-stage: #12101c; // 심우주 자정 — 저채도 짙은 남보라 (파스텔 검사 무관: 저채도·저명도)
@include stage($gx-stage);
$gx-ink: #0b0a13; // 관측창 바닥 — 무대보다 한 톤 어두운 보라검
$gx-glow: #b7c8ff; // 은하 A 별빛 — 파스텔 페리윙클(고명도라 vivid 아님)
$gx-hot: #ffdf9e; // 은하 B 코어 — 파스텔 앰버
$gx-text: #d8d4e6; // 라벨 글자 — 밝은 회보라
.gx {
// 렌더러가 읽는 색 — JS 는 getComputedStyle 로 --gx-* 를 받아 쓴다
--gx-ink: #{$gx-ink};
--gx-glow: #{$gx-glow};
--gx-hot: #{$gx-hot};
--gx-tail: #{$subject-pink};
display: flex; flex-direction: column; gap: $sp-2;
width: 100%; max-width: 424px;
}
.gx__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: $gx-text;
}
.gx__field {
position: relative; height: 180px;
border-radius: $r-card; overflow: hidden;
background: $gx-ink;
box-shadow: inset 0 0 0 1px rgba($gx-text, .18);
}
.gx__field:focus-visible { outline: 2px solid $gx-glow; outline-offset: 2px; }
.gx__cv { display: block; width: 100%; height: 100%; }
.gx__bar { display: flex; align-items: baseline; justify-content: space-between; gap: $sp-2; }
.gx__meta { font-size: 10px; font-weight: 500; color: rgba($gx-text, .72); }
.gx__meta--dim { font-size: 10px; }
@media (max-width: 340px) {
.gx { gap: $sp-1; }
.gx__field { height: 100px; }
.gx__meta--dim { display: none; }
}
// reduce — rAF 를 돌리지 않고 궤적이 다 쌓인 한 장만 남는다.
@media (prefers-reduced-motion: reduce) {
.gx.is-still .gx__field { cursor: default !important; }
}html, body {
margin: 0;
overflow: hidden;
}
.stage {
box-sizing: border-box;
min-height: 100vh;
display: grid;
place-items: center;
margin: 0;
background: #12101c;
font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
padding: clamp(8px, 4vw, 24px);
}
.gx {
--gx-ink: #0b0a13;
--gx-glow: #b7c8ff;
--gx-hot: #ffdf9e;
--gx-tail: #ff9ebb;
display: flex;
flex-direction: column;
gap: 8px;
width: 100%;
max-width: 424px;
}
.gx__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: #d8d4e6;
}
.gx__field {
position: relative;
height: 180px;
border-radius: 16px;
overflow: hidden;
background: #0b0a13;
box-shadow: inset 0 0 0 1px rgba(216, 212, 230, 0.18);
}
.gx__field:focus-visible {
outline: 2px solid #b7c8ff;
outline-offset: 2px;
}
.gx__cv {
display: block;
width: 100%;
height: 100%;
}
.gx__bar {
display: flex;
align-items: baseline;
justify-content: space-between;
gap: 8px;
}
.gx__meta {
font-size: 10px;
font-weight: 500;
color: rgba(216, 212, 230, 0.72);
}
.gx__meta--dim {
font-size: 10px;
}
@media (max-width: 340px) {
.gx {
gap: 4px;
}
.gx__field {
height: 100px;
}
.gx__meta--dim {
display: none;
}
}
@media (prefers-reduced-motion: reduce) {
.gx.is-still .gx__field {
cursor: default !important;
}
}// 조석 꼬리 클로즈업(06) — 수천 별 중 딱 한 별의 궤적만 굵게 남기는 장면.
// 계산은 01 과 같은 전 쌍 O(N²) 뉴턴 중력 + leapfrog(근사 아님).
// 다른 점은 렌더 뿐이다:
// - 다른 별은 흐린 점 + 짧은 잔상(집단의 흐름만 보인다)
// - 추적 별(TRACK 인덱스, 원반 바깥쪽에 심는다)은 굵은 앰버 궤적을
// 별도 트레일 버퍼(좌표 180개 링)에 쌓아 lineTo 로 이어 그린다 —
// 두 은하 중심 사이를 왕복(Lissajous)하다 조석 킥에 던져지는 과정이 한 줄로 드러난다.
// "꼬리는 별 하나하나의 궤도가 아니라 궤도의 집합"이라는 08 의 전 단계 시연.
(function () {
// ── 변형 상수 블록 — 아래 값 하나만 바꿔 변형을 만든다 ──
var NSTARS = 340; // 두 은하 합계 별 수
var TRAILN = 180; // 추적 별 궤적 길이(프레임) — 변형 "궤적 길이"가 180→360으로
// ────────────────────────────────────────────────────
var root = document.getElementById('gxRoot');
var field = document.getElementById('gxField');
var cv = document.getElementById('gxCv');
var css = getComputedStyle(root);
function tokRGB(name) {
var s = css.getPropertyValue(name).trim();
var hx = s.length === 4
? s.charAt(1) + s.charAt(1) + s.charAt(2) + s.charAt(2) + s.charAt(3) + s.charAt(3)
: s.slice(1);
return [parseInt(hx.slice(0, 2), 16), parseInt(hx.slice(2, 4), 16), parseInt(hx.slice(4, 6), 16)];
}
var C_INK = tokRGB('--gx-ink');
var C_GLOW = tokRGB('--gx-glow');
var C_HOT = tokRGB('--gx-hot');
var C_TAIL = tokRGB('--gx-tail');
var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
var raf = 0, t0 = -1;
var W = 0, H = 0, dpr = 1;
var chainCv, chainCtx;
var N = 0, X = [], Y = [], VX = [], VY = [];
var TRACK = -1; // 추적 별 인덱스 — seed() 에서 원반 가장자리로 정한다
var trailX = [], trailY = []; // 추적 별 궤적 링 버퍼
function fit() {
var r = field.getBoundingClientRect();
W = Math.round(r.width); H = Math.round(r.height);
dpr = Math.min(2, window.devicePixelRatio || 1);
cv.width = W * dpr; cv.height = H * dpr;
cv.style.width = '100%'; cv.style.height = '100%';
chainCv = document.createElement('canvas');
chainCv.width = W * dpr; chainCv.height = H * dpr;
chainCtx = chainCv.getContext('2d');
chainCtx.scale(dpr, dpr);
}
function mulberry32(seed) {
return function () {
seed |= 0; seed = (seed + 0x6D2B79F5) | 0;
var t = Math.imul(seed ^ (seed >>> 15), 1 | seed);
t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;
return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
};
}
// G·질량은 캔버스 픽셀 단위 시뮬레이션 값(물리 상수 아님 — 글에서 설명)
var G = 140.0, SOFT2 = 16;
var DT = 1 / 60;
var AX = [], AY = [];
function accel() {
// 전 쌍 O(N²) 뉴턴 중력 — a_i = Σ G·(x_j - x_i)/(|d|²+ε²)^1.5 (근사 아님)
var i, j, dx, dy, d2, inv, f;
for (i = 0; i < N; i++) { AX[i] = 0; AY[i] = 0; }
for (i = 0; i < N; i++) {
for (j = i + 1; j < N; j++) {
dx = X[j] - X[i]; dy = Y[j] - Y[i];
d2 = dx * dx + dy * dy + SOFT2;
inv = 1 / Math.sqrt(d2);
f = G * inv * inv * inv;
AX[i] += dx * f; AY[i] += dy * f;
AX[j] -= dx * f; AY[j] -= dy * f;
}
}
}
var aReady = false;
function stepLeap() {
if (!aReady) { accel(); aReady = true; }
var h = DT * 0.5;
for (var i = 0; i < N; i++) {
VX[i] += AX[i] * h; VY[i] += AY[i] * h;
X[i] += VX[i] * DT; Y[i] += VY[i] * DT;
}
accel();
for (var j = 0; j < N; j++) {
VX[j] += AX[j] * h; VY[j] += AY[j] * h;
}
}
function placeDisk(cx, cy, R, count, phase, dvx, dvy, dir, rnd, sc) {
var M = R * R * 0.90;
var start = N;
for (var i = 0; i < count; i++) {
var r = R * Math.sqrt(rnd());
var a = phase + (i / count) * Math.PI * 2 + rnd() * 0.5;
var v = Math.sqrt(M / Math.max(r, 6)) * dir;
X.push(cx + Math.cos(a) * r);
Y.push(cy + Math.sin(a) * r);
VX.push(dvx * sc * 0.30 + -Math.sin(a) * v + (rnd() - 0.5) * 2);
VY.push(dvy * sc * 0.30 + Math.cos(a) * v + (rnd() - 0.5) * 2);
N++;
}
// 추적 별 — 첫 원반 바깥쪽 마지막 별(조석 꼬리가 먼저 잡히는 위치)
if (TRACK < 0 && start === 0) TRACK = N - 1;
}
function seed() {
X = []; Y = []; VX = []; VY = []; N = 0; aReady = false;
TRACK = -1; trailX = []; trailY = [];
var rnd = mulberry32(13);
var half = NSTARS >> 1;
var R = Math.min(W, H) * 0.46;
var sc = R;
placeDisk(W * 0.26, H * 0.30, R, half, 0, 0.62, -0.42, 1.0, rnd, sc);
placeDisk(W * 0.74, H * 0.70, R, NSTARS - half, Math.PI, -0.62, 0.42, 0.85, rnd, sc);
}
function rgba(c, a) { return 'rgba(' + c[0] + ',' + c[1] + ',' + c[2] + ',' + a + ')'; }
function decay() {
// 집단 잔상은 빨리 지운다(궤적이 아니라 흐름만 남긴다) — 추적 궤적은 trail 버퍼가 기억
chainCtx.setTransform(1, 0, 0, 1, 0, 0);
chainCtx.globalCompositeOperation = 'destination-out';
chainCtx.fillStyle = 'rgba(0,0,0,0.028)';
chainCtx.fillRect(0, 0, W * dpr, H * dpr);
chainCtx.globalCompositeOperation = 'source-over';
chainCtx.setTransform(dpr, 0, 0, dpr, 0, 0);
}
var prev = null;
function stamp() {
if (prev) {
for (var i = 0; i < N; i++) {
if (i === TRACK) continue; // 추적 별은 여기 찍지 않는다(굵은 궤적이 대신한다)
chainCtx.strokeStyle = rgba(i < (N >> 1) ? C_GLOW : C_TAIL, 0.26);
chainCtx.lineWidth = 1.6;
chainCtx.beginPath();
chainCtx.moveTo(prev[0][i], prev[1][i]);
chainCtx.lineTo(X[i], Y[i]);
chainCtx.stroke();
}
}
if (!prev) { prev = [X.slice(), Y.slice()]; }
else { prev[0] = X.slice(); prev[1] = Y.slice(); }
// 추적 궤적 링 버퍼 — 오래된 좌표는 밀려난다
trailX.push(X[TRACK]); trailY.push(Y[TRACK]);
if (trailX.length > TRAILN) { trailX.shift(); trailY.shift(); }
}
function draw() {
var ctx = cv.getContext('2d'); // CanvasRenderingContext2D — 이 데모의 그리기 문맥
ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
ctx.fillStyle = rgb(C_INK);
ctx.fillRect(0, 0, W, H);
var rnd = mulberry32(14);
ctx.fillStyle = rgba(C_GLOW, 0.35);
for (var k = 0; k < 40; k++) {
var bx = rnd() * W, by = rnd() * H, br = rnd() * 0.8 + 0.3;
ctx.globalAlpha = 0.12 + rnd() * 0.22;
ctx.beginPath(); ctx.arc(bx, by, br, 0, Math.PI * 2); ctx.fill();
}
ctx.globalAlpha = 1;
ctx.drawImage(chainCv, 0, 0, W, H);
// 추적 궤적 — 굵은 앰버 라인. 오래된 세그먼트일수록 옅게(페이드)
var tn = trailX.length;
if (tn > 1) {
for (var s = 1; s < tn; s++) {
var age = s / tn; // 0 오래됨 → 1 최신
ctx.strokeStyle = rgba(C_HOT, 0.10 + age * 0.75);
ctx.lineWidth = 0.8 + age * 1.9;
ctx.beginPath();
ctx.moveTo(trailX[s - 1], trailY[s - 1]);
ctx.lineTo(trailX[s], trailY[s]);
ctx.stroke();
}
}
// 별 — 집단은 흐린 점, 추적 별은 큰 앰버 글로우 + 코어
for (var i = 0; i < N; i++) {
if (i === TRACK) continue;
var col = i < (N >> 1) ? C_GLOW : C_TAIL;
ctx.fillStyle = rgba(col, 0.11);
ctx.beginPath(); ctx.arc(X[i], Y[i], 3.0, 0, Math.PI * 2); ctx.fill();
ctx.fillStyle = rgba(col, 0.58);
ctx.beginPath(); ctx.arc(X[i], Y[i], 1.5, 0, Math.PI * 2); ctx.fill();
}
ctx.fillStyle = rgba(C_HOT, 0.16);
ctx.beginPath(); ctx.arc(X[TRACK], Y[TRACK], 7.5, 0, Math.PI * 2); ctx.fill();
ctx.fillStyle = rgba(C_HOT, 0.55);
ctx.beginPath(); ctx.arc(X[TRACK], Y[TRACK], 3.6, 0, Math.PI * 2); ctx.fill();
ctx.fillStyle = rgba(C_HOT, 1.0);
ctx.beginPath(); ctx.arc(X[TRACK], Y[TRACK], 1.6, 0, Math.PI * 2); ctx.fill();
// 은하 B 코어 표식
ctx.fillStyle = rgba(C_GLOW, 0.85);
ctx.beginPath(); ctx.arc(X[N >> 1], Y[N >> 1], 2.0, 0, Math.PI * 2); ctx.fill();
}
function rgb(c) { return 'rgb(' + c[0] + ',' + c[1] + ',' + c[2] + ')'; }
var simSteps = 0;
function frame(now) {
if (t0 < 0) t0 = now;
var loop = ((now - t0) / 1000) % 3.0; // 3초 루프 — 스침 → 왕복 → 킥 순간 반복
var target = Math.floor(loop / DT);
while (simSteps < target) { stepLeap(); simSteps++; stamp(); }
if (target < simSteps - 3) { seed(); simSteps = 0; prev = null; chainCtx.clearRect(0, 0, W, H); }
decay();
draw();
raf = requestAnimationFrame(frame);
}
function stillFrame() {
// reduce — 킥 직후까지 적분한 뒤 한 장 고정
for (var s = 0; s < 170; s++) { stepLeap(); stamp(); }
draw();
}
window.addEventListener('resize', function () {
fit(); seed(); simSteps = 0; prev = null; aReady = false;
if (reduce) stillFrame();
});
fit();
seed();
if (reduce) {
stillFrame();
root.classList.add('is-still');
} else {
raf = requestAnimationFrame(frame);
}
})();// GalaxyNbodyTidalTail — vanilla 판(run/322/demo/06-galaxy-nbody-tidal-tail/index.html) 의 React 포트.
// 조석 꼬리 클로즈업 — 수천 별 중 딱 한 별의 궤적만 굵게 남기는 장면.
// 계산은 01 과 같은 전 쌍 O(N²) 뉴턴 중력 + leapfrog(근사 아님).
// 다른 점은 렌더 뿐이다:
// - 다른 별은 흐린 점 + 짧은 잔상(집단의 흐름만 보인다)
// - 추적 별(TRACK 인덱스, 원반 바깥쪽에 심는다)은 굵은 앰버 궤적을
// 별도 트레일 버퍼(좌표 180개 링)에 쌓아 lineTo 로 이어 그린다 —
// 두 은하 중심 사이를 왕복(Lissajous)하다 조석 킥에 던져지는 과정이 한 줄로 드러난다.
import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./GalaxyNbodyTidalTail.module.scss";
export type GalaxyNbodyTidalTailProps = {
duration?: string;
easing?: string;
color?: string;
nstars?: number; // 두 은하 합계 별 수
trailn?: number; // 추적 별 궤적 길이(프레임) — 변형 "궤적 길이"가 180→360으로
};
type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };
type RGB = [number, number, number];
type Sim2D = { N: number; X: number[]; Y: number[]; VX: number[]; VY: number[] };
const FIELD_LABEL = "조석 꼬리 클로즈업 실험판";
// G·질량은 캔버스 픽셀 단위 시뮬레이션 값(물리 상수 아님 — 글에서 설명)
const G = 140.0, SOFT2 = 16;
const DT = 1 / 60;
function mulberry32(seed: number): () => number {
let s = seed | 0;
return function (): number {
s = (s + 0x6D2B79F5) | 0;
let t = Math.imul(s ^ (s >>> 15), 1 | s);
t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;
return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
};
}
export default function GalaxyNbodyTidalTail({
duration = "2s",
easing = "cubic-bezier(.2, .8, .2, 1)",
color = "#b7c8ff",
nstars = 340,
trailn = 180
}: GalaxyNbodyTidalTailProps) {
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 colRef = useRef<{ ink: RGB; glow: RGB; hot: RGB; tail: RGB } | null>(null);
const chainCvRef = useRef<HTMLCanvasElement | null>(null);
const chainCtxRef = useRef<CanvasRenderingContext2D | null>(null);
const nstarsRef = useRef(nstars) as Box<number>;
const trailnRef = useRef(trailn) as Box<number>;
const wRef = useRef(0) as Box<number>;
const hRef = useRef(0) as Box<number>;
const dprRef = useRef(1) as Box<number>;
const rafRef = useRef(0) as Box<number>;
const [still, setStill] = useState(false);
const vars: Vars = { "--duration": duration, "--easing": easing, "--color": color };
function reduced(): boolean {
return window.matchMedia("(prefers-reduced-motion: reduce)").matches;
}
function tokRGB(root: HTMLDivElement, name: string): RGB {
const s = getComputedStyle(root).getPropertyValue(name).trim();
const hx = s.length === 4
? s.charAt(1) + s.charAt(1) + s.charAt(2) + s.charAt(2) + s.charAt(3) + s.charAt(3)
: s.slice(1);
return [parseInt(hx.slice(0, 2), 16), parseInt(hx.slice(2, 4), 16), parseInt(hx.slice(4, 6), 16)];
}
function rgba(c: RGB, a: number): string {
return "rgba(" + c[0] + "," + c[1] + "," + c[2] + "," + a + ")";
}
function rgb(c: RGB): string {
return "rgb(" + c[0] + "," + c[1] + "," + c[2] + ")";
}
const simRef = useRef({ N: 0, X: [] as number[], Y: [] as number[], VX: [] as number[], VY: [] as number[] }) as Box<Sim2D>;
const AXRef = useRef<number[]>([]) as Box<number[]>;
const AYRef = useRef<number[]>([]) as Box<number[]>;
const aReadyRef = useRef(false) as Box<boolean>;
const prevRef = useRef<[number[], number[]] | null>(null);
const simStepsRef = useRef(0) as Box<number>;
const trackRef = useRef(-1) as Box<number>; // 추적 별 인덱스 — seed() 에서 원반 가장자리로 정한다
const trailXRef = useRef<number[]>([]) as Box<number[]>;
const trailYRef = useRef<number[]>([]) as Box<number[]>;
function fit(): void {
const field = fieldRef.current;
const cv = cvRef.current;
if (!field || !cv) return;
const r = field.getBoundingClientRect();
const W = Math.round(r.width), H = Math.round(r.height);
const dpr = Math.min(2, window.devicePixelRatio || 1);
wRef.current = W; hRef.current = H; dprRef.current = dpr;
cv.width = W * dpr; cv.height = H * dpr;
cv.style.width = "100%"; cv.style.height = "100%";
ctxRef.current = cv.getContext("2d");
const chainCv = document.createElement("canvas");
chainCv.width = W * dpr; chainCv.height = H * dpr;
const chainCtx = chainCv.getContext("2d");
if (chainCtx) chainCtx.scale(dpr, dpr);
chainCvRef.current = chainCv;
chainCtxRef.current = chainCtx;
}
function accel(): void {
// 전 쌍 O(N²) 뉴턴 중력 — a_i = Σ G·(x_j - x_i)/(|d|²+ε²)^1.5 (근사 아님)
const sim = simRef.current;
const AX = AXRef.current, AY = AYRef.current;
const N = sim.N;
let i: number, j: number, dx: number, dy: number, d2: number, inv: number, f: number;
for (i = 0; i < N; i++) { AX[i] = 0; AY[i] = 0; }
for (i = 0; i < N; i++) {
for (j = i + 1; j < N; j++) {
dx = sim.X[j] - sim.X[i]; dy = sim.Y[j] - sim.Y[i];
d2 = dx * dx + dy * dy + SOFT2;
inv = 1 / Math.sqrt(d2);
f = G * inv * inv * inv;
AX[i] += dx * f; AY[i] += dy * f;
AX[j] -= dx * f; AY[j] -= dy * f;
}
}
}
function stepLeap(): void {
const sim = simRef.current;
const AX = AXRef.current, AY = AYRef.current;
if (!aReadyRef.current) { accel(); aReadyRef.current = true; }
const h = DT * 0.5;
for (let i = 0; i < sim.N; i++) {
sim.VX[i] += AX[i] * h; sim.VY[i] += AY[i] * h;
sim.X[i] += sim.VX[i] * DT; sim.Y[i] += sim.VY[i] * DT;
}
accel();
for (let j = 0; j < sim.N; j++) {
sim.VX[j] += AX[j] * h; sim.VY[j] += AY[j] * h;
}
}
function placeDisk(cx: number, cy: number, R: number, count: number, phase: number, dvx: number, dvy: number, dir: number, rnd: () => number, sc: number): void {
const sim = simRef.current;
const M = R * R * 0.90;
const start = sim.N;
for (let i = 0; i < count; i++) {
const r = R * Math.sqrt(rnd());
const a = phase + (i / count) * Math.PI * 2 + rnd() * 0.5;
const v = Math.sqrt(M / Math.max(r, 6)) * dir;
sim.X.push(cx + Math.cos(a) * r);
sim.Y.push(cy + Math.sin(a) * r);
sim.VX.push(dvx * sc * 0.30 + -Math.sin(a) * v + (rnd() - 0.5) * 2);
sim.VY.push(dvy * sc * 0.30 + Math.cos(a) * v + (rnd() - 0.5) * 2);
sim.N++;
}
// 추적 별 — 첫 원반 바깥쪽 마지막 별(조석 꼬리가 먼저 잡히는 위치)
if (trackRef.current < 0 && start === 0) trackRef.current = sim.N - 1;
}
function seed(): void {
const sim = simRef.current;
sim.X = []; sim.Y = []; sim.VX = []; sim.VY = []; sim.N = 0;
aReadyRef.current = false;
trackRef.current = -1;
trailXRef.current = []; trailYRef.current = [];
const rnd = mulberry32(13);
const half = nstarsRef.current >> 1;
const W = wRef.current, H = hRef.current;
const R = Math.min(W, H) * 0.46;
const sc = R;
placeDisk(W * 0.26, H * 0.30, R, half, 0, 0.62, -0.42, 1.0, rnd, sc);
placeDisk(W * 0.74, H * 0.70, R, nstarsRef.current - half, Math.PI, -0.62, 0.42, 0.85, rnd, sc);
}
function decay(): void {
// 집단 잔상은 빨리 지운다(궤적이 아니라 흐름만 남긴다) — 추적 궤적은 trail 버퍼가 기억
const chainCtx = chainCtxRef.current;
const dpr = dprRef.current;
const W = wRef.current, H = hRef.current;
if (!chainCtx) return;
chainCtx.setTransform(1, 0, 0, 1, 0, 0);
chainCtx.globalCompositeOperation = "destination-out";
chainCtx.fillStyle = "rgba(0,0,0,0.028)";
chainCtx.fillRect(0, 0, W * dpr, H * dpr);
chainCtx.globalCompositeOperation = "source-over";
chainCtx.setTransform(dpr, 0, 0, dpr, 0, 0);
}
function stamp(): void {
const chainCtx = chainCtxRef.current;
const col = colRef.current;
const sim = simRef.current;
const prev = prevRef.current;
if (!chainCtx || !col) return;
if (prev) {
for (let i = 0; i < sim.N; i++) {
if (i === trackRef.current) continue; // 추적 별은 여기 찍지 않는다(굵은 궤적이 대신한다)
chainCtx.strokeStyle = rgba(i < (sim.N >> 1) ? col.glow : col.tail, 0.26);
chainCtx.lineWidth = 1.6;
chainCtx.beginPath();
chainCtx.moveTo(prev[0][i], prev[1][i]);
chainCtx.lineTo(sim.X[i], sim.Y[i]);
chainCtx.stroke();
}
}
if (!prev) prevRef.current = [sim.X.slice(), sim.Y.slice()];
else { prev[0] = sim.X.slice(); prev[1] = sim.Y.slice(); }
// 추적 궤적 링 버퍼 — 오래된 좌표는 밀려난다
trailXRef.current.push(sim.X[trackRef.current]);
trailYRef.current.push(sim.Y[trackRef.current]);
if (trailXRef.current.length > trailnRef.current) { trailXRef.current.shift(); trailYRef.current.shift(); }
}
function draw(): void {
const ctx = ctxRef.current;
const chainCv = chainCvRef.current;
const col = colRef.current;
const dpr = dprRef.current;
const sim = simRef.current;
const W = wRef.current, H = hRef.current;
if (!ctx || !chainCv || !col) return;
ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
ctx.fillStyle = rgb(col.ink);
ctx.fillRect(0, 0, W, H);
const rnd = mulberry32(14);
ctx.fillStyle = rgba(col.glow, 0.35);
for (let k = 0; k < 40; k++) {
const bx = rnd() * W, by = rnd() * H, br = rnd() * 0.8 + 0.3;
ctx.globalAlpha = 0.12 + rnd() * 0.22;
ctx.beginPath(); ctx.arc(bx, by, br, 0, Math.PI * 2); ctx.fill();
}
ctx.globalAlpha = 1;
ctx.drawImage(chainCv, 0, 0, W, H);
// 추적 궤적 — 굵은 앰버 라인. 오래된 세그먼트일수록 옅게(페이드)
const trailX = trailXRef.current, trailY = trailYRef.current;
const tn = trailX.length;
if (tn > 1) {
for (let s = 1; s < tn; s++) {
const age = s / tn; // 0 오래됨 → 1 최신
ctx.strokeStyle = rgba(col.hot, 0.10 + age * 0.75);
ctx.lineWidth = 0.8 + age * 1.9;
ctx.beginPath();
ctx.moveTo(trailX[s - 1], trailY[s - 1]);
ctx.lineTo(trailX[s], trailY[s]);
ctx.stroke();
}
}
// 별 — 집단은 흐린 점, 추적 별은 큰 앰버 글로우 + 코어
const trk = trackRef.current;
for (let i = 0; i < sim.N; i++) {
if (i === trk) continue;
const c = i < (sim.N >> 1) ? col.glow : col.tail;
ctx.fillStyle = rgba(c, 0.11);
ctx.beginPath(); ctx.arc(sim.X[i], sim.Y[i], 3.0, 0, Math.PI * 2); ctx.fill();
ctx.fillStyle = rgba(c, 0.58);
ctx.beginPath(); ctx.arc(sim.X[i], sim.Y[i], 1.5, 0, Math.PI * 2); ctx.fill();
}
ctx.fillStyle = rgba(col.hot, 0.16);
ctx.beginPath(); ctx.arc(sim.X[trk], sim.Y[trk], 7.5, 0, Math.PI * 2); ctx.fill();
ctx.fillStyle = rgba(col.hot, 0.55);
ctx.beginPath(); ctx.arc(sim.X[trk], sim.Y[trk], 3.6, 0, Math.PI * 2); ctx.fill();
ctx.fillStyle = rgba(col.hot, 1.0);
ctx.beginPath(); ctx.arc(sim.X[trk], sim.Y[trk], 1.6, 0, Math.PI * 2); ctx.fill();
// 은하 B 코어 표식
ctx.fillStyle = rgba(col.glow, 0.85);
ctx.beginPath(); ctx.arc(sim.X[sim.N >> 1], sim.Y[sim.N >> 1], 2.0, 0, Math.PI * 2); ctx.fill();
}
function stillFrame(): void {
// reduce — 킥 직후까지 적분한 뒤 한 장 고정
for (let s = 0; s < 170; s++) { stepLeap(); stamp(); }
draw();
}
let t0 = -1;
function frame(now: number): void {
if (t0 < 0) t0 = now;
const loop = ((now - t0) / 1000) % 3.0; // 3초 루프 — 스침 → 왕복 → 킥 순간 반복
const target = Math.floor(loop / DT);
while (simStepsRef.current < target) { stepLeap(); simStepsRef.current++; stamp(); }
if (target < simStepsRef.current - 3) {
seed(); simStepsRef.current = 0; prevRef.current = null;
const chainCtx = chainCtxRef.current;
if (chainCtx) chainCtx.clearRect(0, 0, wRef.current, hRef.current);
}
decay();
draw();
rafRef.current = requestAnimationFrame(frame);
}
useEffect(() => {
const root = rootRef.current;
if (!root) return;
nstarsRef.current = nstars;
trailnRef.current = trailn;
colRef.current = {
ink: tokRGB(root, "--gx-ink"),
glow: tokRGB(root, "--gx-glow"),
hot: tokRGB(root, "--gx-hot"),
tail: tokRGB(root, "--gx-tail"),
};
fit();
seed();
simStepsRef.current = 0;
prevRef.current = null;
function onResize(): void {
fit(); seed(); simStepsRef.current = 0; prevRef.current = null; aReadyRef.current = false;
if (reduced()) stillFrame();
}
window.addEventListener("resize", onResize);
if (reduced()) {
stillFrame();
setStill(true);
} else {
t0 = -1;
rafRef.current = requestAnimationFrame(frame);
}
return () => {
window.removeEventListener("resize", onResize);
cancelAnimationFrame(rafRef.current);
};
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [nstars, trailn]);
const rootCls = still ? `${styles.root} ${styles.isStill}` : styles.root;
return (
<main className={styles.stage}>
<div className={rootCls} ref={rootRef} style={vars}>
<p className={styles.hint}>
<span>수천 별 중 한 별만 궤적을 남기면, 꼬리가 만들어지는 순간 그 별이 두 중심 사이를 왕복하다 던져집니다</span>
</p>
<div
className={styles.field}
ref={fieldRef}
role="application"
aria-label={FIELD_LABEL}
tabIndex={0}
>
<canvas className={styles.cv} ref={cvRef}></canvas>
</div>
<div className={styles.bar}>
<span className={styles.meta}>별 340개 · 추적 1개 궤적</span>
<span className={styles.metaDim}>canvas · one-star trail · requestAnimationFrame</span>
</div>
</div>
</main>
);
}06 Tidal tail close-up — the fling seen through one star's trail — Measured area 20.762% · moving frames 23/23Original by GODRICH · SCSS and React ship in the zip · N Body Simulation, 9 Ways (Galaxy, No Library)
The post this demo lives in
N Body Simulation, 9 Ways (Galaxy, No Library)No library, no WebGL — integrate Newtonian gravity on every star, every frame, and two galaxies shear past, throwing tid See all demos in this post
If you like this effect - similar demos
Creative UI03 Drawing a star — coefficients sorted by size, one stroke of the penFourier Epicycles, 9 Ways (No Library)
Creative UI01 Butterfly basics — three differential equations, one Euler step at a timeLorenz Attractor: 9 Butterfly Chaos Demos
Creative UI01 The basic strike — one layer of midpoint displacement halving a segment9 Lightning Effect Background Scenes, No WebGL