04A Gridless Snake Whose Chain Body Is Dragged Behind the Head by Distance Constraints
The head steers toward the food while the other segments coast on inertia and a constraint pulls each back to a fixed distance from its neighbor, so the body bends in smooth curves.
Best forFree-movement snake and worm characters
SEG_GAPSTEER_RATESEG_COUNTFOLLOW_ITER
<main class="stage">
<div class="sc is-demo" id="scRoot">
<canvas class="sc__canvas" id="scCanvas" width="480" height="300" tabindex="0" aria-label="A Gridless Snake Whose Chain Body Is Dragged Behind the Head by Distance Constraints"></canvas>
<p class="sc__status" id="scStatus" aria-live="polite">Auto steering</p>
<button class="sc__btn" id="scBtn" type="button">Pause</button>
<p class="sc__caption">A Gridless Snake Whose Chain Body Is Dragged Behind the Head by Distance Constraints</p>
</div>
</main>@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-ink);
.sc {
position: relative;
width: min(92vw, calc(160vh - 12.8vw));
aspect-ratio: 480 / 300;
margin: 0 auto;
border-radius: $r-card;
overflow: hidden;
box-shadow: $shadow-raised;
background: $subject-ink;
}
.sc__canvas {
display: block;
width: 100%;
height: 100%;
touch-action: none;
}
.sc__canvas:focus-visible {
outline: 2px solid rgba(255, 255, 255, .85);
outline-offset: -6px;
}
.sc__status {
position: absolute;
left: $sp-3;
top: $sp-3;
max-width: 62%;
margin: 0;
padding: $sp-1 $sp-3;
border-radius: $r-pill;
background: rgba(255, 255, 255, .85);
color: $subject-ink;
font-weight: 500;
font-size: 11px;
line-height: 1.4;
pointer-events: none;
}
.sc__btn {
position: absolute;
right: $sp-3;
bottom: $sp-3;
margin: 0;
padding: $sp-1 $sp-3;
border: 0;
border-radius: $r-pill;
background: rgba(255, 255, 255, .85);
color: $subject-ink;
font: inherit;
font-weight: 500;
font-size: 12px;
line-height: 1.4;
cursor: pointer;
}
.sc__btn:focus-visible {
outline: 2px solid #ffffff;
outline-offset: 2px;
}
.sc__caption {
position: absolute;
left: $sp-3;
bottom: $sp-3;
max-width: 68%;
margin: 0;
padding: $sp-1 $sp-3;
border-radius: $r-pill;
background: rgba(255, 255, 255, .85);
color: $subject-ink;
font-weight: 500;
font-size: 12px;
line-height: 1.4;
pointer-events: none;
}
@media (max-width: 340px) {
.sc__caption, .sc__btn { font-size: 10px; padding: $sp-1 $sp-2; }
.sc__status { font-size: 10px; }
}
@media (prefers-reduced-motion: reduce) {
.sc { cursor: default; }
}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);
}
.sc {
position: relative;
width: min(92vw, 160vh - 12.8vw);
aspect-ratio: 480/300;
margin: 0 auto;
border-radius: 16px;
overflow: hidden;
box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
background: #17141a;
}
.sc__canvas {
display: block;
width: 100%;
height: 100%;
touch-action: none;
}
.sc__canvas:focus-visible {
outline: 2px solid rgba(255, 255, 255, 0.85);
outline-offset: -6px;
}
.sc__status {
position: absolute;
left: 12px;
top: 12px;
max-width: 62%;
margin: 0;
padding: 4px 12px;
border-radius: 999px;
background: rgba(255, 255, 255, 0.85);
color: #17141a;
font-weight: 500;
font-size: 11px;
line-height: 1.4;
pointer-events: none;
}
.sc__btn {
position: absolute;
right: 12px;
bottom: 12px;
margin: 0;
padding: 4px 12px;
border: 0;
border-radius: 999px;
background: rgba(255, 255, 255, 0.85);
color: #17141a;
font: inherit;
font-weight: 500;
font-size: 12px;
line-height: 1.4;
cursor: pointer;
}
.sc__btn:focus-visible {
outline: 2px solid #ffffff;
outline-offset: 2px;
}
.sc__caption {
position: absolute;
left: 12px;
bottom: 12px;
max-width: 68%;
margin: 0;
padding: 4px 12px;
border-radius: 999px;
background: rgba(255, 255, 255, 0.85);
color: #17141a;
font-weight: 500;
font-size: 12px;
line-height: 1.4;
pointer-events: none;
}
@media (max-width: 340px) {
.sc__caption, .sc__btn {
font-size: 10px;
padding: 4px 8px;
}
.sc__status {
font-size: 10px;
}
}
@media (prefers-reduced-motion: reduce) {
.sc {
cursor: default;
}
}(function () {
const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const REDUCE_STEP_MS = 900;
const IDLE_TICKS = 150;
const BTN_PAUSE = 'Pause';
const BTN_PLAY = 'Play';
const BTN_NEXT = 'Next scene';
// 파스텔 팔레트 — 어두운 판 위에 밝은 색을 얹어 명도 차로 읽힌다
const BG = [29, 26, 44];
const TILE_A = [37, 33, 58];
const TILE_B = [42, 38, 66];
const MINT = [126, 226, 192];
const SKY = [124, 196, 255];
const LILAC = [190, 164, 255];
const PINK = [255, 160, 190];
const PEACH = [255, 208, 168];
const CREAM = [255, 244, 224];
function clamp(v, lo, hi) { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a, b, k) { return a + (b - a) * k; }
function smooth(x) { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function rgba(c, a) {
return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + clamp(a, 0, 1).toFixed(3) + ')';
}
function mix(a, b, k) {
return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)];
}
// 시드 고정 난수 — 같은 시드면 언제나 같은 수열 (선형 합동 방식)
function lcg(seed) {
let s = seed >>> 0;
return function () {
s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
return s / 4294967296;
};
}
// 정수 두 개로 0 이상 1 미만의 값을 만드는 해시 (같은 입력은 늘 같은 값)
function hash2(x, y, seed) {
let h = (Math.imul(x | 0, 374761393) + Math.imul(y | 0, 668265263) + Math.imul(seed | 0, 1442695041)) | 0;
h = Math.imul(h ^ (h >>> 13), 1274126177);
h ^= h >>> 16;
return (h >>> 0) / 4294967296;
}
function glow(ctx, x, y, r, c, a) {
const g = ctx.createRadialGradient(x, y, 0, x, y, r);
g.addColorStop(0, rgba(c, a));
g.addColorStop(1, rgba(c, 0));
ctx.fillStyle = g;
ctx.fillRect(x - r, y - r, r * 2, r * 2);
}
// 둥근 사각형 경로 (roundRect 가 없는 브라우저에서도 같은 모양)
function rrPath(ctx, x, y, w, h, r) {
const rr = Math.min(r, w / 2, h / 2);
ctx.beginPath();
ctx.moveTo(x + rr, y);
ctx.arcTo(x + w, y, x + w, y + h, rr);
ctx.arcTo(x + w, y + h, x, y + h, rr);
ctx.arcTo(x, y + h, x, y, rr);
ctx.arcTo(x, y, x + w, y, rr);
ctx.closePath();
}
function makeBoard(rows) {
const cell = H / rows;
const cols = Math.floor(W / cell + 1e-6);
return { cols: cols, rows: rows, cell: cell, ox: (W - cols * cell) / 2, oy: 0, n: cols * rows };
}
const DX = [0, 1, 0, -1];
const DY = [-1, 0, 1, 0];
// 칸 번호 y*cols+x. 판 밖이면 -1 (wrap 이면 반대편으로 이어진다)
function cellAt(b, x, y, wrap) {
let xx = x;
let yy = y;
if (wrap) {
xx = (x % b.cols + b.cols) % b.cols;
yy = (y % b.rows + b.rows) % b.rows;
}
else if (x < 0 || y < 0 || x >= b.cols || y >= b.rows) {
return -1;
}
return yy * b.cols + xx;
}
function neighborCell(b, i, d, wrap) {
return cellAt(b, (i % b.cols) + DX[d], Math.floor(i / b.cols) + DY[d], wrap);
}
// 목표 칸에서 너비 우선으로 퍼지는 거리장. blocked 칸과 닿지 못하는 칸은 -1
function distField(b, target, blocked, wrap) {
const dist = new Int16Array(b.n).fill(-1);
const queue = new Int16Array(b.n);
let qh = 0;
let qt = 0;
dist[target] = 0;
queue[qt] = target;
qt += 1;
while (qh < qt) {
const c = queue[qh];
qh += 1;
for (let d = 0; d < 4; d += 1) {
const nb = neighborCell(b, c, d, wrap);
if (nb >= 0 && dist[nb] < 0 && blocked[nb] === 0) {
dist[nb] = dist[c] + 1;
queue[qt] = nb;
qt += 1;
}
}
}
return dist;
}
// 거리장에서 값이 가장 낮은 이웃 (없으면 -1)
function lowestNeighbor(b, dist, from, wrap) {
let best = -1;
let bv = 32000;
for (let d = 0; d < 4; d += 1) {
const nb = neighborCell(b, from, d, wrap);
if (nb >= 0 && dist[nb] >= 0 && dist[nb] < bv) {
bv = dist[nb];
best = nb;
}
}
return best;
}
function pathFrom(b, dist, head, wrap) {
const path = [];
let cur = head;
for (let k = 0; k < b.n; k += 1) {
const nx = lowestNeighbor(b, dist, cur, wrap);
if (nx < 0 || (dist[nx] >= dist[cur] && cur !== head)) {
return [];
}
path.push(nx);
if (dist[nx] === 0) {
return path;
}
cur = nx;
}
return [];
}
function placeFood(g) {
const used = new Uint8Array(g.b.n);
for (let i = 0; i < g.body.length; i += 1) {
used[g.body[i]] = 1;
}
const free = [];
for (let i = 0; i < g.b.n; i += 1) {
if (used[i] === 0) {
free.push(i);
}
}
g.food = free.length > 0 ? free[Math.floor(g.rnd() * free.length)] : -1;
}
function resetGame(g) {
const b = g.b;
const hx = Math.floor(b.cols / 2);
const hy = Math.floor(b.rows / 2);
g.body = [hy * b.cols + hx, hy * b.cols + hx - 1, hy * b.cols + hx - 2];
g.prev = g.body.slice();
g.dead = false;
g.resets += 1;
placeFood(g);
}
function newGame(b, wrap, seed) {
const g = { b: b, wrap: wrap, body: [], prev: [], food: -1, rnd: lcg(seed), eaten: 0, dead: false, resets: -1 };
resetGame(g);
return g;
}
// 머리를 next 칸으로 옮긴다. 먹으면 true, 몸에 부딪히면 dead
function moveSnake(g, next) {
g.prev = g.body.slice();
const ate = next === g.food;
const tail = g.body[g.body.length - 1];
for (let i = 0; i < g.body.length; i += 1) {
if (g.body[i] === next && !(i === g.body.length - 1 && !ate && next === tail)) {
g.dead = true;
return false;
}
}
g.body.unshift(next);
if (ate) {
g.eaten += 1;
placeFood(g);
}
else {
g.body.pop();
}
return ate;
}
// 경로를 끝까지 따라가 먹은 뒤의 가상 몸
function simulate(body, path) {
const v = body.slice();
for (let k = 0; k < path.length; k += 1) {
v.unshift(path[k]);
if (k < path.length - 1) {
v.pop();
}
}
return v;
}
// 가상 몸의 머리에서 번져 나가 꼬리에 닿는가. mark 를 주면 닿은 칸을 표시한다
function tailReachable(b, v, wrap, mark) {
const blocked = new Uint8Array(b.n);
for (let i = 1; i < v.length - 1; i += 1) {
blocked[v[i]] = 1;
}
const tail = v[v.length - 1];
const head = v[0];
const seen = new Uint8Array(b.n);
const stack = [head];
seen[head] = 1;
let hit = false;
while (stack.length > 0) {
const c = stack.pop();
for (let d = 0; d < 4; d += 1) {
const nb = neighborCell(b, c, d, wrap);
if (nb < 0 || seen[nb] === 1) {
continue;
}
if (nb === tail) {
hit = true;
continue;
}
if (blocked[nb] === 1 || nb === head) {
continue;
}
seen[nb] = 1;
stack.push(nb);
}
}
if (mark) {
mark.set(seen);
}
return hit;
}
// 한 수를 정한다: 먹이까지 최단 경로 → (안전 검사) → 막히면 꼬리를 쫓는다
function planMove(g, safeOn) {
const b = g.b;
const head = g.body[0];
const tail = g.body[g.body.length - 1];
const plan = { next: -1, path: [], rejected: [], trap: new Uint8Array(b.n), chase: false };
const blocked = new Uint8Array(b.n);
for (let i = 0; i < g.body.length - 1; i += 1) {
blocked[g.body[i]] = 1;
}
if (g.food >= 0) {
const dist = distField(b, g.food, blocked, g.wrap);
const path = pathFrom(b, dist, head, g.wrap);
plan.path = path;
if (path.length > 0) {
if (!safeOn) {
plan.next = path[0];
return plan;
}
const v = simulate(g.body, path);
if (tailReachable(b, v, g.wrap, plan.trap)) {
plan.next = path[0];
return plan;
}
plan.rejected = path;
}
}
plan.chase = true;
const dist2 = distField(b, tail, blocked, g.wrap);
const nx = lowestNeighbor(b, dist2, head, g.wrap);
if (nx >= 0) {
plan.next = nx;
return plan;
}
for (let d = 0; d < 4; d += 1) {
const nb = neighborCell(b, head, d, g.wrap);
if (nb >= 0 && blocked[nb] === 0 && nb !== head) {
plan.next = nb;
return plan;
}
}
return plan;
}
// 칸 중심의 화면 좌표
function cellX(b, i) { return b.ox + ((i % b.cols) + 0.5) * b.cell; }
function cellY(b, i) { return b.oy + (Math.floor(i / b.cols) + 0.5) * b.cell; }
function wrapDelta(a, c, n, wrap) {
let d = c - a;
if (wrap) {
if (d > n / 2) {
d -= n;
}
if (d < -n / 2) {
d += n;
}
}
return d;
}
// Segments i 의 보간 위치 (칸 좌표). 지난 틱의 자리에서 이번 틱의 자리로 p(0~1) 만큼
function segPos(g, i, p) {
const b = g.b;
const cur = g.body[i];
const pv = i < g.prev.length ? g.prev[i] : cur;
const cx = cur % b.cols;
const cy = Math.floor(cur / b.cols);
const px = pv % b.cols;
const py = Math.floor(pv / b.cols);
return [px + wrapDelta(px, cx, b.cols, g.wrap) * p, py + wrapDelta(py, cy, b.rows, g.wrap) * p];
}
function drawTiles(ctx, b) {
ctx.fillStyle = rgba(BG, 1);
ctx.fillRect(0, 0, W, H);
for (let y = 0; y < b.rows; y += 1) {
for (let x = 0; x < b.cols; x += 1) {
ctx.fillStyle = rgba((x + y) % 2 === 0 ? TILE_A : TILE_B, 1);
ctx.fillRect(b.ox + x * b.cell, b.oy + y * b.cell, b.cell + 0.5, b.cell + 0.5);
}
}
}
function drawFood(ctx, b, food, t) {
if (food < 0) {
return;
}
const x = cellX(b, food);
const y = cellY(b, food);
const pulse = 0.5 + 0.5 * Math.sin(t * 0.12);
glow(ctx, x, y, b.cell * (1.3 + 0.35 * pulse), PINK, 0.55);
ctx.fillStyle = rgba(PINK, 1);
ctx.beginPath();
ctx.arc(x, y, b.cell * 0.3, 0, PI2);
ctx.fill();
ctx.fillStyle = rgba(CREAM, 0.9);
ctx.beginPath();
ctx.arc(x - b.cell * 0.08, y - b.cell * 0.09, b.cell * 0.09, 0, PI2);
ctx.fill();
}
function bodyColor(i, len) {
return mix(MINT, SKY, len <= 1 ? 0 : i / (len - 1));
}
// 칸 중심 (x,y 칸 좌표, 소수 허용)에 Segments 하나
function drawSeg(ctx, b, gx, gy, c, shrink) {
const s = b.cell * (1 - shrink);
const cx = b.ox + (gx + 0.5) * b.cell;
const cy = b.oy + (gy + 0.5) * b.cell;
ctx.fillStyle = rgba(c, 1);
rrPath(ctx, cx - s / 2, cy - s / 2, s, s, s * 0.32);
ctx.fill();
}
function drawEyes(ctx, b, gx, gy, dirx, diry) {
const cx = b.ox + (gx + 0.5) * b.cell;
const cy = b.oy + (gy + 0.5) * b.cell;
const px = -diry;
const py = dirx;
const r = b.cell * 0.09;
ctx.fillStyle = rgba(BG, 1);
for (let s = -1; s <= 1; s += 2) {
ctx.beginPath();
ctx.arc(cx + dirx * b.cell * 0.16 + px * s * b.cell * 0.18, cy + diry * b.cell * 0.16 + py * s * b.cell * 0.18, r, 0, PI2);
ctx.fill();
}
}
function headDir(g) {
if (g.body.length < 2) {
return [1, 0];
}
const b = g.b;
const dx = wrapDelta(g.body[1] % b.cols, g.body[0] % b.cols, b.cols, g.wrap);
const dy = wrapDelta(Math.floor(g.body[1] / b.cols), Math.floor(g.body[0] / b.cols), b.rows, g.wrap);
return [clamp(dx, -1, 1), clamp(dy, -1, 1)];
}
// 보간 없이 칸 그대로 그리는 기본 뱀
function drawSnakeCells(ctx, g, dim) {
const len = g.body.length;
for (let i = len - 1; i >= 0; i -= 1) {
const c = g.body[i];
const col = mix(bodyColor(i, len), BG, dim);
drawSeg(ctx, g.b, c % g.b.cols, Math.floor(c / g.b.cols), col, 0.08);
}
const hd = headDir(g);
drawEyes(ctx, g.b, g.body[0] % g.b.cols, Math.floor(g.body[0] / g.b.cols), hd[0], hd[1]);
}
function start(root, canvas, statusEl, btnEl, make) {
const ctx0 = canvas.getContext('2d');
if (!ctx0) {
return function () { return; };
}
const ctx = ctx0;
const dpr = Math.min(window.devicePixelRatio || 1, 2);
canvas.width = Math.round(W * dpr);
canvas.height = Math.round(H * dpr);
ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
const inp = { x: W / 2, y: H / 2, idle: 99999 };
const scene = make(inp, reduce);
let paused = false;
let rafId = 0;
let lastTs = -1;
let accMs = 0;
let lastLabel = '';
const cleaners = [];
function listen(target, type, fn) {
target.addEventListener(type, fn);
cleaners.push(function () { target.removeEventListener(type, fn); });
}
function show() {
scene.draw(ctx);
const t = scene.label();
if (t !== lastLabel) {
lastLabel = t;
statusEl.textContent = t;
}
}
function advance(ms) {
const n = Math.round(ms / FIXED_DT);
for (let i = 0; i < n; i += 1) {
inp.idle += 1;
scene.step();
}
}
// 움직임 줄이기에서는 루프가 없으니 입력 직후 한 틱쯤 앞으로 보내 바로 그린다
function refresh() {
if (reduce) {
advance(FIXED_DT * 8);
show();
}
}
function toLocal(e) {
const r = canvas.getBoundingClientRect();
inp.x = clamp((e.clientX - r.left) * W / r.width, 0, W);
inp.y = clamp((e.clientY - r.top) * H / r.height, 0, H);
inp.idle = 0;
}
function tick(ts) {
if (lastTs < 0) {
lastTs = ts;
}
const frameDt = Math.min(ts - lastTs, 160);
lastTs = ts;
if (!paused) {
accMs += frameDt;
while (accMs >= FIXED_DT) {
inp.idle += 1;
scene.step();
accMs -= FIXED_DT;
}
show();
}
rafId = requestAnimationFrame(tick);
}
btnEl.textContent = reduce ? BTN_NEXT : BTN_PAUSE;
if (reduce) {
root.classList.remove('is-demo');
advance(1400);
show();
}
listen(btnEl, 'click', function () {
if (reduce) {
advance(REDUCE_STEP_MS);
show();
return;
}
paused = !paused;
if (paused) {
root.classList.remove('is-demo');
}
else {
root.classList.add('is-demo');
}
btnEl.textContent = paused ? BTN_PLAY : BTN_PAUSE;
});
listen(canvas, 'pointermove', function (e) {
toLocal(e);
refresh();
});
listen(canvas, 'pointerdown', function (e) {
toLocal(e);
scene.tap();
refresh();
});
listen(canvas, 'keydown', function (e) {
const k = e.key;
if (k === 'Enter' || k === ' ') {
e.preventDefault();
scene.tap();
refresh();
return;
}
// 이 장면이 쓰는 키만 막는다. 쓰지 않는 키(Tab 등)는 그대로 둔다
if (scene.key(k)) {
e.preventDefault();
refresh();
}
});
if (!reduce) {
rafId = requestAnimationFrame(tick);
}
return function () {
cancelAnimationFrame(rafId);
for (let i = 0; i < cleaners.length; i += 1) {
cleaners[i]();
}
};
}
const SEG_GAP = 9;
const SEG_COUNT = 26;
const SEG_MAX = 40;
const STEER_RATE = 0.075;
const FOLLOW_ITER = 4;
const FOLLOW_STIFF = 0.85;
const SPEED = 2.3;
const DAMP = 0.97;
const EAT_R = 11;
const WALL_PAD = 34;
const KEY_HOLD = 36;
const TRAIL_KEEP = 0.34;
const TXT_AUTO = 'Auto steering';
const TXT_POINTER = 'Chasing the pointer';
const TXT_KEYS = 'Arrow-key steering';
const TXT_LEN = 'Segments';
const TXT_SCORE = 'Eaten';
function makeScene(inp, reduce) {
const rnd = lcg(455404);
const px = [];
const py = [];
const qx = [];
const qy = [];
let ang = 0.3;
let fx = 0;
let fy = 0;
let t = 0;
let eaten = 0;
let keyAng = 0;
let keyLeft = 0;
let count = SEG_COUNT;
let painted = false;
function placeFoodAt() {
fx = 40 + rnd() * (W - 80);
fy = 36 + rnd() * (H - 72);
}
placeFoodAt();
for (let i = 0; i < SEG_MAX; i += 1) {
px.push(W * 0.3 - i * SEG_GAP);
py.push(H * 0.55);
qx.push(px[i]);
qy.push(py[i]);
}
function angDiff(a, c) {
let d = c - a;
while (d > Math.PI) {
d -= PI2;
}
while (d < -Math.PI) {
d += PI2;
}
return d;
}
const scene = {
step() {
t += 1;
let goalX = fx;
let goalY = fy;
if (inp.idle < IDLE_TICKS) {
goalX = inp.x;
goalY = inp.y;
}
let want = Math.atan2(goalY - py[0], goalX - px[0]);
if (keyLeft > 0) {
keyLeft -= 1;
want = keyAng;
}
// 벽 가까이에서는 판 가운데 쪽으로 틀어 준다
if (px[0] < WALL_PAD || px[0] > W - WALL_PAD || py[0] < WALL_PAD || py[0] > H - WALL_PAD) {
want = Math.atan2(H / 2 - py[0], W / 2 - px[0]);
}
ang += clamp(angDiff(ang, want), -STEER_RATE, STEER_RATE) + Math.sin(t * 0.11) * 0.018;
// 머리만 직접 움직이고 나머지 마디는 이전 위치와의 차이(관성)로 나아간다
qx[0] = px[0];
qy[0] = py[0];
px[0] += Math.cos(ang) * SPEED;
py[0] += Math.sin(ang) * SPEED;
for (let i = 1; i < count; i += 1) {
const vx = (px[i] - qx[i]) * DAMP;
const vy = (py[i] - qy[i]) * DAMP;
qx[i] = px[i];
qy[i] = py[i];
px[i] += vx;
py[i] += vy;
}
// 거리 제약: 이웃 마디와의 간격을 SEG_GAP 으로 되돌린다
for (let it = 0; it < FOLLOW_ITER; it += 1) {
for (let i = 1; i < count; i += 1) {
const dx = px[i] - px[i - 1];
const dy = py[i] - py[i - 1];
const d = Math.sqrt(dx * dx + dy * dy) || 0.0001;
const k = ((d - SEG_GAP) / d) * FOLLOW_STIFF;
if (i === 1) {
px[i] -= dx * k;
py[i] -= dy * k;
}
else {
px[i] -= dx * k * 0.5;
py[i] -= dy * k * 0.5;
px[i - 1] += dx * k * 0.5;
py[i - 1] += dy * k * 0.5;
}
}
}
const ex = px[0] - fx;
const ey = py[0] - fy;
if (ex * ex + ey * ey < EAT_R * EAT_R) {
eaten += 1;
if (count < SEG_MAX) {
count += 1;
px[count - 1] = px[count - 2];
py[count - 1] = py[count - 2];
qx[count - 1] = px[count - 1];
qy[count - 1] = py[count - 1];
}
placeFoodAt();
}
},
draw(ctx) {
// 배경을 반투명으로 덮어 지난 자리가 몇 프레임 남게 한다 (첫 프레임만 불투명)
ctx.fillStyle = rgba(BG, painted ? TRAIL_KEEP : 1);
ctx.fillRect(0, 0, W, H);
painted = true;
// 바닥 격자 — 칸 없는 판이라는 걸 보여 주려고 아주 옅게
ctx.strokeStyle = rgba(LILAC, 0.1);
ctx.lineWidth = 1;
for (let x = 0; x <= W; x += 30) {
ctx.beginPath();
ctx.moveTo(x, 0);
ctx.lineTo(x, H);
ctx.stroke();
}
for (let y = 0; y <= H; y += 30) {
ctx.beginPath();
ctx.moveTo(0, y);
ctx.lineTo(W, y);
ctx.stroke();
}
const pulse = 0.5 + 0.5 * Math.sin(t * 0.12);
glow(ctx, fx, fy, 22 + 6 * pulse, PINK, 0.6);
ctx.fillStyle = rgba(PINK, 1);
ctx.beginPath();
ctx.arc(fx, fy, 6.5, 0, PI2);
ctx.fill();
// 지난 자리 잔상 — 이전 위치(qx,qy)에서 지금 위치로 끄는 꼬리빛
for (let i = count - 1; i >= 0; i -= 1) {
const f = i / count;
const c = mix(MINT, SKY, f);
glow(ctx, qx[i], qy[i], 13 - 5 * f, c, 0.22);
}
for (let i = count - 1; i >= 0; i -= 1) {
const f = i / count;
const r = 6.4 - 3.4 * f;
ctx.fillStyle = rgba(mix(MINT, SKY, f), 1);
ctx.beginPath();
ctx.arc(px[i], py[i], r, 0, PI2);
ctx.fill();
}
ctx.fillStyle = rgba(BG, 1);
for (let s = -1; s <= 1; s += 2) {
ctx.beginPath();
ctx.arc(px[0] + Math.cos(ang) * 2.4 - Math.sin(ang) * s * 2.8, py[0] + Math.sin(ang) * 2.4 + Math.cos(ang) * s * 2.8, 1.3, 0, PI2);
ctx.fill();
}
},
label() {
const mode = keyLeft > 0 ? TXT_KEYS : (inp.idle < IDLE_TICKS ? TXT_POINTER : TXT_AUTO);
return mode + ' · ' + TXT_LEN + ' ' + count + ' · ' + TXT_SCORE + ' ' + eaten;
},
tap() {
placeFoodAt();
},
key(k) {
if (k === 'ArrowLeft') {
keyAng = Math.PI;
}
else if (k === 'ArrowRight') {
keyAng = 0;
}
else if (k === 'ArrowUp') {
keyAng = -Math.PI / 2;
}
else if (k === 'ArrowDown') {
keyAng = Math.PI / 2;
}
else {
return false;
}
keyLeft = KEY_HOLD;
return true;
}
};
if (reduce) {
for (let i = 0; i < 60; i += 1) {
scene.step();
}
}
return scene;
}
start(document.getElementById('scRoot'), document.getElementById('scCanvas'), document.getElementById('scStatus'), document.getElementById('scBtn'), makeScene);
})();import { useEffect, useRef } from "react";
import styles from "./SkChainFollowRope.module.scss";
const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const REDUCE_STEP_MS = 900;
const IDLE_TICKS = 150;
const BTN_PAUSE = '멈춤';
const BTN_PLAY = '재생';
const BTN_NEXT = '다음 장면';
type RGB = [number, number, number];
interface Input { x: number; y: number; idle: number; }
interface Scene {
step(): void;
draw(ctx: CanvasRenderingContext2D): void;
label(): string;
tap(): void;
key(k: string): boolean;
}
type Maker = (inp: Input, reduce: boolean) => Scene;
// 파스텔 팔레트 — 어두운 판 위에 밝은 색을 얹어 명도 차로 읽힌다
const BG: RGB = [29, 26, 44];
const TILE_A: RGB = [37, 33, 58];
const TILE_B: RGB = [42, 38, 66];
const MINT: RGB = [126, 226, 192];
const SKY: RGB = [124, 196, 255];
const LILAC: RGB = [190, 164, 255];
const PINK: RGB = [255, 160, 190];
const PEACH: RGB = [255, 208, 168];
const CREAM: RGB = [255, 244, 224];
function clamp(v: number, lo: number, hi: number): number { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a: number, b: number, k: number): number { return a + (b - a) * k; }
function smooth(x: number): number { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function rgba(c: RGB, a: number): string {
return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + clamp(a, 0, 1).toFixed(3) + ')';
}
function mix(a: RGB, b: RGB, k: number): RGB {
return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)];
}
// 시드 고정 난수 — 같은 시드면 언제나 같은 수열 (선형 합동 방식)
function lcg(seed: number): () => number {
let s = seed >>> 0;
return function (): number {
s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
return s / 4294967296;
};
}
// 정수 두 개로 0 이상 1 미만의 값을 만드는 해시 (같은 입력은 늘 같은 값)
function hash2(x: number, y: number, seed: number): number {
let h = (Math.imul(x | 0, 374761393) + Math.imul(y | 0, 668265263) + Math.imul(seed | 0, 1442695041)) | 0;
h = Math.imul(h ^ (h >>> 13), 1274126177);
h ^= h >>> 16;
return (h >>> 0) / 4294967296;
}
function glow(ctx: CanvasRenderingContext2D, x: number, y: number, r: number, c: RGB, a: number): void {
const g = ctx.createRadialGradient(x, y, 0, x, y, r);
g.addColorStop(0, rgba(c, a));
g.addColorStop(1, rgba(c, 0));
ctx.fillStyle = g;
ctx.fillRect(x - r, y - r, r * 2, r * 2);
}
// 둥근 사각형 경로 (roundRect 가 없는 브라우저에서도 같은 모양)
function rrPath(ctx: CanvasRenderingContext2D, x: number, y: number, w: number, h: number, r: number): void {
const rr = Math.min(r, w / 2, h / 2);
ctx.beginPath();
ctx.moveTo(x + rr, y);
ctx.arcTo(x + w, y, x + w, y + h, rr);
ctx.arcTo(x + w, y + h, x, y + h, rr);
ctx.arcTo(x, y + h, x, y, rr);
ctx.arcTo(x, y, x + w, y, rr);
ctx.closePath();
}
// ---- 판과 뱀 ----
interface Board { cols: number; rows: number; cell: number; ox: number; oy: number; n: number; }
function makeBoard(rows: number): Board {
const cell = H / rows;
const cols = Math.floor(W / cell + 1e-6);
return { cols: cols, rows: rows, cell: cell, ox: (W - cols * cell) / 2, oy: 0, n: cols * rows };
}
const DX = [0, 1, 0, -1];
const DY = [-1, 0, 1, 0];
// 칸 번호 y*cols+x. 판 밖이면 -1 (wrap 이면 반대편으로 이어진다)
function cellAt(b: Board, x: number, y: number, wrap: boolean): number {
let xx = x;
let yy = y;
if (wrap) {
xx = (x % b.cols + b.cols) % b.cols;
yy = (y % b.rows + b.rows) % b.rows;
} else if (x < 0 || y < 0 || x >= b.cols || y >= b.rows) {
return -1;
}
return yy * b.cols + xx;
}
function neighborCell(b: Board, i: number, d: number, wrap: boolean): number {
return cellAt(b, (i % b.cols) + DX[d], Math.floor(i / b.cols) + DY[d], wrap);
}
// 목표 칸에서 너비 우선으로 퍼지는 거리장. blocked 칸과 닿지 못하는 칸은 -1
function distField(b: Board, target: number, blocked: Uint8Array, wrap: boolean): Int16Array {
const dist = new Int16Array(b.n).fill(-1);
const queue = new Int16Array(b.n);
let qh = 0;
let qt = 0;
dist[target] = 0;
queue[qt] = target;
qt += 1;
while (qh < qt) {
const c = queue[qh];
qh += 1;
for (let d = 0; d < 4; d += 1) {
const nb = neighborCell(b, c, d, wrap);
if (nb >= 0 && dist[nb] < 0 && blocked[nb] === 0) {
dist[nb] = dist[c] + 1;
queue[qt] = nb;
qt += 1;
}
}
}
return dist;
}
// 거리장에서 값이 가장 낮은 이웃 (없으면 -1)
function lowestNeighbor(b: Board, dist: Int16Array, from: number, wrap: boolean): number {
let best = -1;
let bv = 32000;
for (let d = 0; d < 4; d += 1) {
const nb = neighborCell(b, from, d, wrap);
if (nb >= 0 && dist[nb] >= 0 && dist[nb] < bv) {
bv = dist[nb];
best = nb;
}
}
return best;
}
function pathFrom(b: Board, dist: Int16Array, head: number, wrap: boolean): number[] {
const path: number[] = [];
let cur = head;
for (let k = 0; k < b.n; k += 1) {
const nx = lowestNeighbor(b, dist, cur, wrap);
if (nx < 0 || (dist[nx] >= dist[cur] && cur !== head)) {
return [];
}
path.push(nx);
if (dist[nx] === 0) {
return path;
}
cur = nx;
}
return [];
}
interface Game {
b: Board;
wrap: boolean;
body: number[];
prev: number[];
food: number;
rnd: () => number;
eaten: number;
dead: boolean;
resets: number;
}
function placeFood(g: Game): void {
const used = new Uint8Array(g.b.n);
for (let i = 0; i < g.body.length; i += 1) {
used[g.body[i]] = 1;
}
const free: number[] = [];
for (let i = 0; i < g.b.n; i += 1) {
if (used[i] === 0) {
free.push(i);
}
}
g.food = free.length > 0 ? free[Math.floor(g.rnd() * free.length)] : -1;
}
function resetGame(g: Game): void {
const b = g.b;
const hx = Math.floor(b.cols / 2);
const hy = Math.floor(b.rows / 2);
g.body = [hy * b.cols + hx, hy * b.cols + hx - 1, hy * b.cols + hx - 2];
g.prev = g.body.slice();
g.dead = false;
g.resets += 1;
placeFood(g);
}
function newGame(b: Board, wrap: boolean, seed: number): Game {
const g: Game = { b: b, wrap: wrap, body: [], prev: [], food: -1, rnd: lcg(seed), eaten: 0, dead: false, resets: -1 };
resetGame(g);
return g;
}
// 머리를 next 칸으로 옮긴다. 먹으면 true, 몸에 부딪히면 dead
function moveSnake(g: Game, next: number): boolean {
g.prev = g.body.slice();
const ate = next === g.food;
const tail = g.body[g.body.length - 1];
for (let i = 0; i < g.body.length; i += 1) {
if (g.body[i] === next && !(i === g.body.length - 1 && !ate && next === tail)) {
g.dead = true;
return false;
}
}
g.body.unshift(next);
if (ate) {
g.eaten += 1;
placeFood(g);
} else {
g.body.pop();
}
return ate;
}
// 경로를 끝까지 따라가 먹은 뒤의 가상 몸
function simulate(body: number[], path: number[]): number[] {
const v = body.slice();
for (let k = 0; k < path.length; k += 1) {
v.unshift(path[k]);
if (k < path.length - 1) {
v.pop();
}
}
return v;
}
// 가상 몸의 머리에서 번져 나가 꼬리에 닿는가. mark 를 주면 닿은 칸을 표시한다
function tailReachable(b: Board, v: number[], wrap: boolean, mark: Uint8Array | null): boolean {
const blocked = new Uint8Array(b.n);
for (let i = 1; i < v.length - 1; i += 1) {
blocked[v[i]] = 1;
}
const tail = v[v.length - 1];
const head = v[0];
const seen = new Uint8Array(b.n);
const stack: number[] = [head];
seen[head] = 1;
let hit = false;
while (stack.length > 0) {
const c = stack.pop() as number;
for (let d = 0; d < 4; d += 1) {
const nb = neighborCell(b, c, d, wrap);
if (nb < 0 || seen[nb] === 1) {
continue;
}
if (nb === tail) {
hit = true;
continue;
}
if (blocked[nb] === 1 || nb === head) {
continue;
}
seen[nb] = 1;
stack.push(nb);
}
}
if (mark) {
mark.set(seen);
}
return hit;
}
interface Plan { next: number; path: number[]; rejected: number[]; trap: Uint8Array; chase: boolean; }
// 한 수를 정한다: 먹이까지 최단 경로 → (안전 검사) → 막히면 꼬리를 쫓는다
function planMove(g: Game, safeOn: boolean): Plan {
const b = g.b;
const head = g.body[0];
const tail = g.body[g.body.length - 1];
const plan: Plan = { next: -1, path: [], rejected: [], trap: new Uint8Array(b.n), chase: false };
const blocked = new Uint8Array(b.n);
for (let i = 0; i < g.body.length - 1; i += 1) {
blocked[g.body[i]] = 1;
}
if (g.food >= 0) {
const dist = distField(b, g.food, blocked, g.wrap);
const path = pathFrom(b, dist, head, g.wrap);
plan.path = path;
if (path.length > 0) {
if (!safeOn) {
plan.next = path[0];
return plan;
}
const v = simulate(g.body, path);
if (tailReachable(b, v, g.wrap, plan.trap)) {
plan.next = path[0];
return plan;
}
plan.rejected = path;
}
}
plan.chase = true;
const dist2 = distField(b, tail, blocked, g.wrap);
const nx = lowestNeighbor(b, dist2, head, g.wrap);
if (nx >= 0) {
plan.next = nx;
return plan;
}
for (let d = 0; d < 4; d += 1) {
const nb = neighborCell(b, head, d, g.wrap);
if (nb >= 0 && blocked[nb] === 0 && nb !== head) {
plan.next = nb;
return plan;
}
}
return plan;
}
// 칸 중심의 화면 좌표
function cellX(b: Board, i: number): number { return b.ox + ((i % b.cols) + 0.5) * b.cell; }
function cellY(b: Board, i: number): number { return b.oy + (Math.floor(i / b.cols) + 0.5) * b.cell; }
function wrapDelta(a: number, c: number, n: number, wrap: boolean): number {
let d = c - a;
if (wrap) {
if (d > n / 2) { d -= n; }
if (d < -n / 2) { d += n; }
}
return d;
}
// 마디 i 의 보간 위치 (칸 좌표). 지난 틱의 자리에서 이번 틱의 자리로 p(0~1) 만큼
function segPos(g: Game, i: number, p: number): [number, number] {
const b = g.b;
const cur = g.body[i];
const pv = i < g.prev.length ? g.prev[i] : cur;
const cx = cur % b.cols;
const cy = Math.floor(cur / b.cols);
const px = pv % b.cols;
const py = Math.floor(pv / b.cols);
return [px + wrapDelta(px, cx, b.cols, g.wrap) * p, py + wrapDelta(py, cy, b.rows, g.wrap) * p];
}
function drawTiles(ctx: CanvasRenderingContext2D, b: Board): void {
ctx.fillStyle = rgba(BG, 1);
ctx.fillRect(0, 0, W, H);
for (let y = 0; y < b.rows; y += 1) {
for (let x = 0; x < b.cols; x += 1) {
ctx.fillStyle = rgba((x + y) % 2 === 0 ? TILE_A : TILE_B, 1);
ctx.fillRect(b.ox + x * b.cell, b.oy + y * b.cell, b.cell + 0.5, b.cell + 0.5);
}
}
}
function drawFood(ctx: CanvasRenderingContext2D, b: Board, food: number, t: number): void {
if (food < 0) {
return;
}
const x = cellX(b, food);
const y = cellY(b, food);
const pulse = 0.5 + 0.5 * Math.sin(t * 0.12);
glow(ctx, x, y, b.cell * (1.3 + 0.35 * pulse), PINK, 0.55);
ctx.fillStyle = rgba(PINK, 1);
ctx.beginPath();
ctx.arc(x, y, b.cell * 0.3, 0, PI2);
ctx.fill();
ctx.fillStyle = rgba(CREAM, 0.9);
ctx.beginPath();
ctx.arc(x - b.cell * 0.08, y - b.cell * 0.09, b.cell * 0.09, 0, PI2);
ctx.fill();
}
function bodyColor(i: number, len: number): RGB {
return mix(MINT, SKY, len <= 1 ? 0 : i / (len - 1));
}
// 칸 중심 (x,y 칸 좌표, 소수 허용)에 마디 하나
function drawSeg(ctx: CanvasRenderingContext2D, b: Board, gx: number, gy: number, c: RGB, shrink: number): void {
const s = b.cell * (1 - shrink);
const cx = b.ox + (gx + 0.5) * b.cell;
const cy = b.oy + (gy + 0.5) * b.cell;
ctx.fillStyle = rgba(c, 1);
rrPath(ctx, cx - s / 2, cy - s / 2, s, s, s * 0.32);
ctx.fill();
}
function drawEyes(ctx: CanvasRenderingContext2D, b: Board, gx: number, gy: number, dirx: number, diry: number): void {
const cx = b.ox + (gx + 0.5) * b.cell;
const cy = b.oy + (gy + 0.5) * b.cell;
const px = -diry;
const py = dirx;
const r = b.cell * 0.09;
ctx.fillStyle = rgba(BG, 1);
for (let s = -1; s <= 1; s += 2) {
ctx.beginPath();
ctx.arc(cx + dirx * b.cell * 0.16 + px * s * b.cell * 0.18, cy + diry * b.cell * 0.16 + py * s * b.cell * 0.18, r, 0, PI2);
ctx.fill();
}
}
function headDir(g: Game): [number, number] {
if (g.body.length < 2) {
return [1, 0];
}
const b = g.b;
const dx = wrapDelta(g.body[1] % b.cols, g.body[0] % b.cols, b.cols, g.wrap);
const dy = wrapDelta(Math.floor(g.body[1] / b.cols), Math.floor(g.body[0] / b.cols), b.rows, g.wrap);
return [clamp(dx, -1, 1), clamp(dy, -1, 1)];
}
// 보간 없이 칸 그대로 그리는 기본 뱀
function drawSnakeCells(ctx: CanvasRenderingContext2D, g: Game, dim: number): void {
const len = g.body.length;
for (let i = len - 1; i >= 0; i -= 1) {
const c = g.body[i];
const col = mix(bodyColor(i, len), BG, dim);
drawSeg(ctx, g.b, c % g.b.cols, Math.floor(c / g.b.cols), col, 0.08);
}
const hd = headDir(g);
drawEyes(ctx, g.b, g.body[0] % g.b.cols, Math.floor(g.body[0] / g.b.cols), hd[0], hd[1]);
}
function start(root: HTMLElement, canvas: HTMLCanvasElement, statusEl: HTMLElement, btnEl: HTMLElement, make: Maker): () => void {
const ctx0 = canvas.getContext('2d');
if (!ctx0) {
return function (): void { return; };
}
const ctx: CanvasRenderingContext2D = ctx0;
const dpr = Math.min(window.devicePixelRatio || 1, 2);
canvas.width = Math.round(W * dpr);
canvas.height = Math.round(H * dpr);
ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
const inp: Input = { x: W / 2, y: H / 2, idle: 99999 };
const scene = make(inp, reduce);
let paused = false;
let rafId = 0;
let lastTs = -1;
let accMs = 0;
let lastLabel = '';
const cleaners: Array<() => void> = [];
function listen(target: EventTarget, type: string, fn: (e: Event) => void): void {
target.addEventListener(type, fn);
cleaners.push(function (): void { target.removeEventListener(type, fn); });
}
function show(): void {
scene.draw(ctx);
const t = scene.label();
if (t !== lastLabel) {
lastLabel = t;
statusEl.textContent = t;
}
}
function advance(ms: number): void {
const n = Math.round(ms / FIXED_DT);
for (let i = 0; i < n; i += 1) {
inp.idle += 1;
scene.step();
}
}
// 움직임 줄이기에서는 루프가 없으니 입력 직후 한 틱쯤 앞으로 보내 바로 그린다
function refresh(): void {
if (reduce) {
advance(FIXED_DT * 8);
show();
}
}
function toLocal(e: PointerEvent): void {
const r = canvas.getBoundingClientRect();
inp.x = clamp((e.clientX - r.left) * W / r.width, 0, W);
inp.y = clamp((e.clientY - r.top) * H / r.height, 0, H);
inp.idle = 0;
}
function tick(ts: number): void {
if (lastTs < 0) {
lastTs = ts;
}
const frameDt = Math.min(ts - lastTs, 160);
lastTs = ts;
if (!paused) {
accMs += frameDt;
while (accMs >= FIXED_DT) {
inp.idle += 1;
scene.step();
accMs -= FIXED_DT;
}
show();
}
rafId = requestAnimationFrame(tick);
}
btnEl.textContent = reduce ? BTN_NEXT : BTN_PAUSE;
if (reduce) {
root.classList.remove('is-demo');
advance(1400);
show();
}
listen(btnEl, 'click', function (): void {
if (reduce) {
advance(REDUCE_STEP_MS);
show();
return;
}
paused = !paused;
if (paused) {
root.classList.remove('is-demo');
} else {
root.classList.add('is-demo');
}
btnEl.textContent = paused ? BTN_PLAY : BTN_PAUSE;
});
listen(canvas, 'pointermove', function (e: Event): void {
toLocal(e as PointerEvent);
refresh();
});
listen(canvas, 'pointerdown', function (e: Event): void {
toLocal(e as PointerEvent);
scene.tap();
refresh();
});
listen(canvas, 'keydown', function (e: Event): void {
const k = (e as KeyboardEvent).key;
if (k === 'Enter' || k === ' ') {
e.preventDefault();
scene.tap();
refresh();
return;
}
// 이 장면이 쓰는 키만 막는다. 쓰지 않는 키(Tab 등)는 그대로 둔다
if (scene.key(k)) {
e.preventDefault();
refresh();
}
});
if (!reduce) {
rafId = requestAnimationFrame(tick);
}
return function (): void {
cancelAnimationFrame(rafId);
for (let i = 0; i < cleaners.length; i += 1) {
cleaners[i]();
}
};
}
const SEG_GAP = 9;
const SEG_COUNT = 26;
const SEG_MAX = 40;
const STEER_RATE = 0.075;
const FOLLOW_ITER = 4;
const FOLLOW_STIFF = 0.85;
const SPEED = 2.3;
const DAMP = 0.97;
const EAT_R = 11;
const WALL_PAD = 34;
const KEY_HOLD = 36;
const TRAIL_KEEP = 0.34;
const TXT_AUTO = '자동 조향';
const TXT_POINTER = '포인터를 쫓는 중';
const TXT_KEYS = '방향키 조종';
const TXT_LEN = '마디';
const TXT_SCORE = '먹이';
function makeScene(inp: Input, reduce: boolean): Scene {
const rnd = lcg(455404);
const px: number[] = [];
const py: number[] = [];
const qx: number[] = [];
const qy: number[] = [];
let ang = 0.3;
let fx = 0;
let fy = 0;
let t = 0;
let eaten = 0;
let keyAng = 0;
let keyLeft = 0;
let count = SEG_COUNT;
let painted = false;
function placeFoodAt(): void {
fx = 40 + rnd() * (W - 80);
fy = 36 + rnd() * (H - 72);
}
placeFoodAt();
for (let i = 0; i < SEG_MAX; i += 1) {
px.push(W * 0.3 - i * SEG_GAP);
py.push(H * 0.55);
qx.push(px[i]);
qy.push(py[i]);
}
function angDiff(a: number, c: number): number {
let d = c - a;
while (d > Math.PI) { d -= PI2; }
while (d < -Math.PI) { d += PI2; }
return d;
}
const scene: Scene = {
step(): void {
t += 1;
let goalX = fx;
let goalY = fy;
if (inp.idle < IDLE_TICKS) {
goalX = inp.x;
goalY = inp.y;
}
let want = Math.atan2(goalY - py[0], goalX - px[0]);
if (keyLeft > 0) {
keyLeft -= 1;
want = keyAng;
}
// 벽 가까이에서는 판 가운데 쪽으로 틀어 준다
if (px[0] < WALL_PAD || px[0] > W - WALL_PAD || py[0] < WALL_PAD || py[0] > H - WALL_PAD) {
want = Math.atan2(H / 2 - py[0], W / 2 - px[0]);
}
ang += clamp(angDiff(ang, want), -STEER_RATE, STEER_RATE) + Math.sin(t * 0.11) * 0.018;
// 머리만 직접 움직이고 나머지 마디는 이전 위치와의 차이(관성)로 나아간다
qx[0] = px[0];
qy[0] = py[0];
px[0] += Math.cos(ang) * SPEED;
py[0] += Math.sin(ang) * SPEED;
for (let i = 1; i < count; i += 1) {
const vx = (px[i] - qx[i]) * DAMP;
const vy = (py[i] - qy[i]) * DAMP;
qx[i] = px[i];
qy[i] = py[i];
px[i] += vx;
py[i] += vy;
}
// 거리 제약: 이웃 마디와의 간격을 SEG_GAP 으로 되돌린다
for (let it = 0; it < FOLLOW_ITER; it += 1) {
for (let i = 1; i < count; i += 1) {
const dx = px[i] - px[i - 1];
const dy = py[i] - py[i - 1];
const d = Math.sqrt(dx * dx + dy * dy) || 0.0001;
const k = ((d - SEG_GAP) / d) * FOLLOW_STIFF;
if (i === 1) {
px[i] -= dx * k;
py[i] -= dy * k;
} else {
px[i] -= dx * k * 0.5;
py[i] -= dy * k * 0.5;
px[i - 1] += dx * k * 0.5;
py[i - 1] += dy * k * 0.5;
}
}
}
const ex = px[0] - fx;
const ey = py[0] - fy;
if (ex * ex + ey * ey < EAT_R * EAT_R) {
eaten += 1;
if (count < SEG_MAX) {
count += 1;
px[count - 1] = px[count - 2];
py[count - 1] = py[count - 2];
qx[count - 1] = px[count - 1];
qy[count - 1] = py[count - 1];
}
placeFoodAt();
}
},
draw(ctx: CanvasRenderingContext2D): void {
// 배경을 반투명으로 덮어 지난 자리가 몇 프레임 남게 한다 (첫 프레임만 불투명)
ctx.fillStyle = rgba(BG, painted ? TRAIL_KEEP : 1);
ctx.fillRect(0, 0, W, H);
painted = true;
// 바닥 격자 — 칸 없는 판이라는 걸 보여 주려고 아주 옅게
ctx.strokeStyle = rgba(LILAC, 0.1);
ctx.lineWidth = 1;
for (let x = 0; x <= W; x += 30) {
ctx.beginPath();
ctx.moveTo(x, 0);
ctx.lineTo(x, H);
ctx.stroke();
}
for (let y = 0; y <= H; y += 30) {
ctx.beginPath();
ctx.moveTo(0, y);
ctx.lineTo(W, y);
ctx.stroke();
}
const pulse = 0.5 + 0.5 * Math.sin(t * 0.12);
glow(ctx, fx, fy, 22 + 6 * pulse, PINK, 0.6);
ctx.fillStyle = rgba(PINK, 1);
ctx.beginPath();
ctx.arc(fx, fy, 6.5, 0, PI2);
ctx.fill();
// 지난 자리 잔상 — 이전 위치(qx,qy)에서 지금 위치로 끄는 꼬리빛
for (let i = count - 1; i >= 0; i -= 1) {
const f = i / count;
const c = mix(MINT, SKY, f);
glow(ctx, qx[i], qy[i], 13 - 5 * f, c, 0.22);
}
for (let i = count - 1; i >= 0; i -= 1) {
const f = i / count;
const r = 6.4 - 3.4 * f;
ctx.fillStyle = rgba(mix(MINT, SKY, f), 1);
ctx.beginPath();
ctx.arc(px[i], py[i], r, 0, PI2);
ctx.fill();
}
ctx.fillStyle = rgba(BG, 1);
for (let s = -1; s <= 1; s += 2) {
ctx.beginPath();
ctx.arc(px[0] + Math.cos(ang) * 2.4 - Math.sin(ang) * s * 2.8, py[0] + Math.sin(ang) * 2.4 + Math.cos(ang) * s * 2.8, 1.3, 0, PI2);
ctx.fill();
}
},
label(): string {
const mode = keyLeft > 0 ? TXT_KEYS : (inp.idle < IDLE_TICKS ? TXT_POINTER : TXT_AUTO);
return mode + ' · ' + TXT_LEN + ' ' + count + ' · ' + TXT_SCORE + ' ' + eaten;
},
tap(): void {
placeFoodAt();
},
key(k: string): boolean {
if (k === 'ArrowLeft') { keyAng = Math.PI; }
else if (k === 'ArrowRight') { keyAng = 0; }
else if (k === 'ArrowUp') { keyAng = -Math.PI / 2; }
else if (k === 'ArrowDown') { keyAng = Math.PI / 2; }
else { return false; }
keyLeft = KEY_HOLD;
return true;
}
};
if (reduce) {
for (let i = 0; i < 60; i += 1) {
scene.step();
}
}
return scene;
}
export default function SkChainFollowRope() {
const rootRef = useRef<HTMLDivElement | null>(null);
const canvasRef = useRef<HTMLCanvasElement | null>(null);
const statusRef = useRef<HTMLParagraphElement | null>(null);
const btnRef = useRef<HTMLButtonElement | null>(null);
useEffect(() => {
const root = rootRef.current;
const canvas = canvasRef.current;
const statusEl = statusRef.current;
const btnEl = btnRef.current;
if (!root || !canvas || !statusEl || !btnEl) return;
return start(root, canvas, statusEl, btnEl, makeScene);
}, []);
return (
<main className={styles.stage}>
<div className={`${styles.sc} is-demo`} ref={rootRef}>
<canvas className={styles.sc__canvas} ref={canvasRef} width={480} height={300} tabIndex={0} aria-label="칸 없이 머리를 따라 거리 제약으로 끌려오는 사슬 몸통의 뱀" />
<p className={styles.sc__status} ref={statusRef} aria-live="polite">자동 조향</p>
<button className={styles.sc__btn} ref={btnRef} type="button">멈춤</button>
<p className={styles.sc__caption}>칸 없이 머리를 따라 거리 제약으로 끌려오는 사슬 몸통의 뱀</p>
</div>
</main>
);
}04 A Gridless Snake Whose Chain Body Is Dragged Behind the Head by Distance Constraints — Measured area 7.728% · moving frames 23/23Original by GODRICH · SCSS and React ship in the zip · CSS Snake Game: 9 Boards That Find Their Own Path
The post this demo lives in
CSS Snake Game: 9 Boards That Find Their Own PathOpen a css snake game and the snake already turns toward the food before you touch a key — scene 01's shortest path and See all demos in this post
If you like this effect - similar demos
game07 The entry editor — a wheel whose labels and angles recompute togetherSpin Wheel: 9 Canvas Roulettes, Flick to Stop
game01 Paddle That Trails the Dragged PositionBrick Breaker Game JavaScript — 9 Physics Patterns
game05 A Maze Where a Spreading Wave Computes the Distance to Every CellMaze Generator: 9 Carve-and-Solve Scenes