02Cars That Stop Behind the Car Ahead With a Gap at Red
Every frame the gap to the car ahead and the distance to the stop line decide acceleration and braking (gap 24 px, brake 0.07, accel 0.04); only cars that can still stop when the light turns yellow aim at the line, so queued cars keep their gap and none crosses on red.
Best forA traffic-flow explainer scene
SAFE_GAPBRAKE_DECELSTOP_LINE_XACCEL
<main class="stage">
<div class="sc is-demo" id="scRoot">
<canvas class="sc__canvas" id="scCanvas" width="480" height="300" tabindex="0" aria-label="Cars That Stop Behind the Car Ahead With a Gap at Red"></canvas>
<p class="sc__status" id="scStatus" aria-live="polite">Green — go</p>
<button class="sc__btn" id="scBtn" type="button">Pause</button>
<p class="sc__caption">Cars That Stop Behind the Car Ahead With a Gap at Red</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 REDUCE_START_MS = 1200;
const KEY_STEP = 12;
const FONT = '-apple-system, "Segoe UI", "Noto Sans KR", sans-serif';
const SIG_GREEN = 0;
const SIG_YELLOW = 1;
const SIG_RED = 2;
const GREEN_RGB = [61, 214, 140];
const YELLOW_RGB = [255, 200, 64];
const RED_RGB = [255, 92, 102];
const SIGNAL_RGBS = [GREEN_RGB, YELLOW_RGB, RED_RGB];
const SKY_RGB = [226, 238, 252];
const GRASS_RGB = [206, 236, 214];
const ROAD_RGB = [188, 192, 212];
const ROAD_EDGE_RGB = [162, 166, 192];
const MARK_RGB = [250, 250, 255];
const INK_RGB = [58, 52, 84];
const CAR_RGBS = [[255, 184, 196], [170, 208, 255], [196, 176, 255], [158, 232, 200], [255, 222, 150], [255, 196, 224]];
const TXT_GO = 'Green — go';
const TXT_READY = 'Yellow — get ready to stop';
const TXT_STOP = 'Red — stop';
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]) + ',' + a.toFixed(3) + ')';
}
// 시드 고정 난수 — 같은 시드면 언제나 같은 수열
function mulberry32(seed) {
let s = seed >>> 0;
return function () {
s = (s + 0x6D2B79F5) >>> 0;
let t = s;
t = Math.imul(t ^ (t >>> 15), t | 1);
t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
};
}
// 격자 점의 값 — 정수 두 개를 섞어 0..1 로 (같은 입력은 언제나 같은 값)
function hash2(ix, iy) {
let h = Math.imul(ix | 0, 374761393) + Math.imul(iy | 0, 668265263);
h = Math.imul(h ^ (h >>> 13), 1274126177);
return ((h ^ (h >>> 16)) >>> 0) / 4294967296;
}
// 2차원 값 잡음 — 네 격자 점을 부드럽게 보간
function vnoise(x, y) {
const ix = Math.floor(x);
const iy = Math.floor(y);
const fx = smooth(x - ix);
const fy = smooth(y - iy);
return lerp(lerp(hash2(ix, iy), hash2(ix + 1, iy), fx), lerp(hash2(ix, iy + 1), hash2(ix + 1, iy + 1), fx), fy);
}
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);
}
function rrect(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();
}
// 주기 [초록, 노랑, 빨강] 프레임 수에서 프레임 f 의 신호 상태
function phaseAt(f, g, y, r) {
const total = g + y + r;
const m = ((f % total) + total) % total;
return m < g ? SIG_GREEN : (m < g + y ? SIG_YELLOW : SIG_RED);
}
function stateText(state) {
return state === SIG_GREEN ? TXT_GO : (state === SIG_YELLOW ? TXT_READY : TXT_STOP);
}
// 신호 상태 -> 빨강·노랑·초록 렌즈 밝기 (위에서 아래)
function litOf(state) {
return [state === SIG_RED ? 1 : 0, state === SIG_YELLOW ? 1 : 0, state === SIG_GREEN ? 1 : 0];
}
const LENS_RGBS = [RED_RGB, YELLOW_RGB, GREEN_RGB];
// 세로 신호등 머리 — 렌즈 세 개와 켜진 렌즈의 빛 번짐
function drawHead(ctx, cx, cy, r, lit) {
const step = r * 2.5;
rrect(ctx, cx - r * 1.45, cy - step - r * 1.45, r * 2.9, step * 2 + r * 2.9, r * 0.9);
ctx.fillStyle = rgba(INK_RGB, 1);
ctx.fill();
for (let i = 0; i < 3; i += 1) {
const ly = cy + (i - 1) * step;
ctx.beginPath();
ctx.arc(cx, ly, r, 0, PI2);
ctx.fillStyle = rgba(LENS_RGBS[i], 0.2 + 0.8 * lit[i]);
ctx.fill();
if (lit[i] > 0.02) {
glow(ctx, cx, ly, r * 3.2, LENS_RGBS[i], 0.55 * lit[i]);
}
}
}
// 위에서 본 차 — 앞 범퍼가 x, 가운데가 y. 제동 중이면 뒷등이 켜진다
function drawCar(ctx, x, y, len, wid, rgb, braking) {
const x0 = x - len;
rrect(ctx, x0, y - wid / 2, len, wid, 6);
ctx.fillStyle = rgba(rgb, 1);
ctx.fill();
rrect(ctx, x - len * 0.62, y - wid / 2 + 3, len * 0.34, wid - 6, 3);
ctx.fillStyle = 'rgba(255,255,255,0.62)';
ctx.fill();
ctx.fillStyle = 'rgba(255,248,214,1)';
ctx.fillRect(x - 3, y - wid / 2 + 2, 3, 4);
ctx.fillRect(x - 3, y + wid / 2 - 6, 3, 4);
ctx.fillStyle = braking ? rgba(RED_RGB, 1) : 'rgba(150,120,150,0.8)';
ctx.fillRect(x0, y - wid / 2 + 2, 3, 4);
ctx.fillRect(x0, y + wid / 2 - 6, 3, 4);
if (braking) {
glow(ctx, x0, y, 12, RED_RGB, 0.45);
}
}
// 한 줄 도로 장면의 바탕 — 잔디 위에 도로띠 하나, 정지선과 횡단보도
function drawLaneBackdrop(ctx, roadY, roadH, stopX, seedTrees) {
ctx.fillStyle = rgba(GRASS_RGB, 1);
ctx.fillRect(0, 0, W, H);
const rnd = mulberry32(seedTrees);
for (let i = 0; i < 14; i += 1) {
const tx = 16 + rnd() * (W - 32);
const up = rnd() < 0.5;
const ty = up ? roadY - roadH / 2 - 22 - rnd() * 26 : roadY + roadH / 2 + 22 + rnd() * 26;
ctx.beginPath();
ctx.arc(tx, ty, 9 + rnd() * 6, 0, PI2);
ctx.fillStyle = 'rgba(160,214,184,0.9)';
ctx.fill();
}
ctx.fillStyle = rgba(ROAD_RGB, 1);
ctx.fillRect(0, roadY - roadH / 2, W, roadH);
ctx.fillStyle = rgba(ROAD_EDGE_RGB, 1);
ctx.fillRect(0, roadY - roadH / 2, W, 2);
ctx.fillRect(0, roadY + roadH / 2 - 2, W, 2);
ctx.fillStyle = rgba(MARK_RGB, 0.8);
for (let x = 6; x < W; x += 36) {
ctx.fillRect(x, roadY - 1, 18, 2);
}
for (let k = 0; k < 5; k += 1) {
ctx.fillRect(stopX + 5, roadY - roadH / 2 + 3 + k * (roadH - 6) / 5, 12, (roadH - 6) / 5 - 3);
}
ctx.fillRect(stopX - 2, roadY - roadH / 2, 3, roadH);
}
// 한 줄 차량 흐름 — 앞차 간격(IDM)과 정지선을 같은 식으로 다룬다. 차는 앞쪽부터 0번이다
class Lane {
constructor(seed, p) {
this.cars = [];
this.nextAt = 0;
this.made = 0;
this.p = p;
this.rnd = mulberry32(seed);
}
accelFor(v, s, vL, g0) {
const p = this.p;
const sStar = g0 + Math.max(0, v * p.headway + v * (v - vL) / (2 * Math.sqrt(p.accel * p.brake)));
return p.accel * (1 - Math.pow(v / p.vmax, p.delta) - Math.pow(sStar / Math.max(s, 0.5), 2));
}
// f 프레임에, 뒤쪽이 비어 있고 때가 됐으면 한 대 들여보낸다
maybeSpawn(f, minGap, maxGap, v0) {
if (f < this.nextAt) {
return false;
}
const last = this.cars.length > 0 ? this.cars[this.cars.length - 1] : null;
if (last && last.x - last.len < this.p.gap + 10) {
return false;
}
const rgb = CAR_RGBS[this.made % CAR_RGBS.length];
this.cars.push({ x: -2, v: v0, len: this.p.len, rgb: rgb, go: false, decided: false, sigK: -1, brake: false, id: this.made });
this.made += 1;
this.nextAt = f + minGap + Math.floor(this.rnd() * (maxGap - minGap + 1));
return true;
}
// 신호 목록은 x 오름차순. 한 번 호출 = 한 프레임. 정지선을 넘은 차(detect 용) id 를 돌려준다
step(sigs, onCross, watchX) {
const p = this.p;
for (let i = 0; i < this.cars.length; i += 1) {
const c = this.cars[i];
let acc = this.accelFor(c.v, 1e6, c.v, p.gap);
if (i > 0) {
const L = this.cars[i - 1];
acc = Math.min(acc, this.accelFor(c.v, (L.x - L.len) - c.x, L.v, p.gap));
}
let k = -1;
for (let j = 0; j < sigs.length; j += 1) {
if (sigs[j].x >= c.x) {
k = j;
break;
}
}
let clampX = 1e9;
if (k >= 0) {
const sg = sigs[k];
if (c.sigK !== k) {
c.sigK = k;
c.decided = false;
c.go = false;
}
if (sg.state === SIG_GREEN) {
c.decided = false;
c.go = false;
}
else {
if (!c.decided) {
c.decided = true;
c.go = c.v * c.v / (2 * p.brake) > sg.x - c.x;
}
if (!c.go) {
acc = Math.min(acc, this.accelFor(c.v, sg.x - c.x - 2, 0, p.lineGap));
clampX = sg.x - 1.5;
}
}
}
acc = Math.max(acc, -p.brake * 3);
const prevX = c.x;
c.v = Math.max(0, c.v + acc);
c.x += c.v;
if (c.x > clampX && prevX <= clampX) {
c.x = clampX;
c.v = 0;
}
c.brake = acc < -0.012 || c.v < 0.05;
if (prevX < watchX && c.x >= watchX) {
onCross(c, watchX);
}
}
while (this.cars.length > 0 && this.cars[0].x - this.cars[0].len > W + 20) {
this.cars.shift();
}
}
// 정지선 뒤에서 서 있는 차 수
waiting(stopX) {
let n = 0;
for (let i = 0; i < this.cars.length; i += 1) {
const c = this.cars[i];
if (c.v < 0.25 && c.x < stopX + 2 && c.x > stopX - 260) {
n += 1;
}
}
return n;
}
}
function main(rootEl, canvas, statusEl, btnEl) {
const ctx0 = canvas.getContext('2d');
if (!ctx0) {
return function () { return; };
}
canvas.width = W;
canvas.height = H;
const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
const scene = makeScene(ctx0, reduce);
if (reduce) {
rootEl.classList.remove('is-demo');
}
let paused = false;
let rafId = 0;
let lastTs = null;
let accMs = 0;
let lastLabel = '';
let px = W / 2;
let py = H / 2;
const cleaners = [];
function listen(target, type, fn) {
target.addEventListener(type, fn);
cleaners.push(function () { target.removeEventListener(type, fn); });
}
function show() {
scene.draw();
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) {
scene.step();
}
}
function setButton() {
btnEl.textContent = reduce ? 'Next scene' : (paused ? 'Play' : 'Pause');
}
function toLocal(e) {
const r = canvas.getBoundingClientRect();
return [clamp((e.clientX - r.left) * W / r.width, 0, W), clamp((e.clientY - r.top) * H / r.height, 0, H)];
}
function moved() {
if (scene.point) {
scene.point(px, py);
}
if (reduce) {
show();
}
}
function onButton() {
if (reduce) {
advance(REDUCE_STEP_MS);
show();
return;
}
paused = !paused;
if (paused) {
rootEl.classList.remove('is-demo');
}
else {
rootEl.classList.add('is-demo');
}
setButton();
}
function onAction() {
if (scene.tap) {
scene.tap();
if (reduce) {
show();
}
return;
}
onButton();
}
function tick(ts) {
if (lastTs === null) {
lastTs = ts;
}
const frameDt = Math.min(ts - lastTs, 160);
lastTs = ts;
if (!paused) {
accMs += frameDt;
while (accMs >= FIXED_DT) {
scene.step();
accMs -= FIXED_DT;
}
show();
}
rafId = requestAnimationFrame(tick);
}
listen(btnEl, 'click', function () { onButton(); });
listen(canvas, 'pointerdown', function (e) {
const p = toLocal(e);
px = p[0];
py = p[1];
moved();
if (scene.tap) {
scene.tap();
if (reduce) {
show();
}
}
});
listen(canvas, 'pointermove', function (e) {
const p = toLocal(e);
px = p[0];
py = p[1];
moved();
});
listen(canvas, 'keydown', function (e) {
const k = e.key;
if (k === 'Enter' || k === ' ') {
e.preventDefault();
onAction();
return;
}
let dx = 0;
let dy = 0;
if (k === 'ArrowLeft') {
dx = -KEY_STEP;
}
else if (k === 'ArrowRight') {
dx = KEY_STEP;
}
else if (k === 'ArrowUp') {
dy = -KEY_STEP;
}
else if (k === 'ArrowDown') {
dy = KEY_STEP;
}
else {
return;
}
e.preventDefault();
px = clamp(px + dx, 0, W);
py = clamp(py + dy, 0, H);
moved();
});
advance(REDUCE_START_MS);
setButton();
show();
if (!reduce) {
rafId = requestAnimationFrame(tick);
}
function destroy() {
cancelAnimationFrame(rafId);
for (let i = 0; i < cleaners.length; i += 1) {
cleaners[i]();
}
}
return destroy;
}
const SAFE_GAP = 24;
const BRAKE_DECEL = 0.07;
const ACCEL = 0.04;
const STOP_LINE_X = 372;
const ROAD_Y = 150;
const ROAD_H = 80;
const CAR_LEN = 46;
const CAR_WID = 30;
const GREEN_LEN = 84;
const YELLOW_LEN = 26;
const RED_LEN = 100;
const FREE_SPEED = 2.2;
const HEADWAY = 10;
const SEED = 446;
function makeScene(ctx, reduce) {
const lane = new Lane(SEED, { accel: ACCEL, brake: BRAKE_DECEL, gap: SAFE_GAP, lineGap: 3, vmax: FREE_SPEED, headway: HEADWAY, delta: 4, len: CAR_LEN });
const sig = { x: STOP_LINE_X, state: SIG_GREEN };
const sigs = [sig];
const cycle = GREEN_LEN + YELLOW_LEN + RED_LEN;
let f = GREEN_LEN - 24;
let skew = 0;
function tickSignal() {
sig.state = phaseAt(f + skew, GREEN_LEN, YELLOW_LEN, RED_LEN);
}
function none(c, x) { return; }
const scene = {
step: function () {
f += 1;
tickSignal();
lane.maybeSpawn(f, 30, 56, FREE_SPEED * 0.9);
lane.step(sigs, none, -1);
},
// 누르면 신호가 지금 상태에서 바로 다음 단계로 넘어간다
tap: function () {
const m = (((f + skew) % cycle) + cycle) % cycle;
const target = sig.state === SIG_RED ? 0 : (sig.state === SIG_GREEN ? GREEN_LEN : GREEN_LEN + YELLOW_LEN);
skew += ((target - m) % cycle + cycle) % cycle;
tickSignal();
},
label: function () { return stateText(sig.state); },
draw: function () {
drawLaneBackdrop(ctx, ROAD_Y, ROAD_H, STOP_LINE_X, 17);
for (let i = 0; i < lane.cars.length; i += 1) {
const c = lane.cars[i];
drawCar(ctx, c.x, ROAD_Y, c.len, CAR_WID, c.rgb, c.brake);
}
// 서 있는 차 사이 간격 — 앞차 뒤꽁무니와 내 앞 범퍼 사이를 칠하고 폭을 적는다
ctx.strokeStyle = rgba(INK_RGB, 0.8);
ctx.lineWidth = 1.5;
ctx.fillStyle = rgba(INK_RGB, 0.9);
ctx.font = '500 10px ' + FONT;
ctx.textAlign = 'center';
for (let i = 1; i < lane.cars.length; i += 1) {
const c = lane.cars[i];
const L = lane.cars[i - 1];
if (c.v < 0.25 && L.v < 0.25) {
const a = c.x;
const b = L.x - L.len;
ctx.fillStyle = rgba(YELLOW_RGB, 0.55);
ctx.fillRect(a, ROAD_Y - CAR_WID / 2, b - a, CAR_WID);
ctx.fillStyle = rgba(INK_RGB, 0.9);
ctx.beginPath();
ctx.moveTo(a, ROAD_Y + CAR_WID / 2 + 7);
ctx.lineTo(b, ROAD_Y + CAR_WID / 2 + 7);
ctx.moveTo(a, ROAD_Y + CAR_WID / 2 + 3);
ctx.lineTo(a, ROAD_Y + CAR_WID / 2 + 11);
ctx.moveTo(b, ROAD_Y + CAR_WID / 2 + 3);
ctx.lineTo(b, ROAD_Y + CAR_WID / 2 + 11);
ctx.stroke();
ctx.fillText(String(Math.round(b - a)), (a + b) / 2, ROAD_Y + CAR_WID / 2 + 22);
}
}
// 신호 — 정지선 위쪽
drawHead(ctx, STOP_LINE_X + 20, ROAD_Y - ROAD_H / 2 - 40, 8, litOf(sig.state));
ctx.fillStyle = rgba(INK_RGB, 1);
ctx.fillRect(STOP_LINE_X + 18, ROAD_Y - ROAD_H / 2 - 8, 4, 8);
}
};
if (reduce) {
tickSignal();
}
for (let i = 0; i < 330; i += 1) {
scene.step();
}
return scene;
}
main(document.getElementById('scRoot'), document.getElementById('scCanvas'), document.getElementById('scStatus'), document.getElementById('scBtn'));
})();import { useEffect, useRef } from "react";
import styles from "./TlCarFollowStopLineGap.module.scss";
const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const REDUCE_STEP_MS = 900;
const REDUCE_START_MS = 1200;
const KEY_STEP = 12;
const FONT = '-apple-system, "Segoe UI", "Noto Sans KR", sans-serif';
const SIG_GREEN = 0;
const SIG_YELLOW = 1;
const SIG_RED = 2;
const GREEN_RGB = [61, 214, 140];
const YELLOW_RGB = [255, 200, 64];
const RED_RGB = [255, 92, 102];
const SIGNAL_RGBS = [GREEN_RGB, YELLOW_RGB, RED_RGB];
const SKY_RGB = [226, 238, 252];
const GRASS_RGB = [206, 236, 214];
const ROAD_RGB = [188, 192, 212];
const ROAD_EDGE_RGB = [162, 166, 192];
const MARK_RGB = [250, 250, 255];
const INK_RGB = [58, 52, 84];
const CAR_RGBS = [[255, 184, 196], [170, 208, 255], [196, 176, 255], [158, 232, 200], [255, 222, 150], [255, 196, 224]];
const TXT_GO = '초록불 — 진행';
const TXT_READY = '노란불 — 정지 준비';
const TXT_STOP = '빨간불 — 정지';
type Pt = [number, number];
interface Scene {
step(): void;
draw(): void;
label(): string;
point?(x: number, y: number): void;
tap?(): void;
}
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: number[], a: number): string {
return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + a.toFixed(3) + ')';
}
// 시드 고정 난수 — 같은 시드면 언제나 같은 수열
function mulberry32(seed: number): () => number {
let s = seed >>> 0;
return function (): number {
s = (s + 0x6D2B79F5) >>> 0;
let t = s;
t = Math.imul(t ^ (t >>> 15), t | 1);
t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
};
}
// 격자 점의 값 — 정수 두 개를 섞어 0..1 로 (같은 입력은 언제나 같은 값)
function hash2(ix: number, iy: number): number {
let h = Math.imul(ix | 0, 374761393) + Math.imul(iy | 0, 668265263);
h = Math.imul(h ^ (h >>> 13), 1274126177);
return ((h ^ (h >>> 16)) >>> 0) / 4294967296;
}
// 2차원 값 잡음 — 네 격자 점을 부드럽게 보간
function vnoise(x: number, y: number): number {
const ix = Math.floor(x);
const iy = Math.floor(y);
const fx = smooth(x - ix);
const fy = smooth(y - iy);
return lerp(lerp(hash2(ix, iy), hash2(ix + 1, iy), fx), lerp(hash2(ix, iy + 1), hash2(ix + 1, iy + 1), fx), fy);
}
function glow(ctx: CanvasRenderingContext2D, x: number, y: number, r: number, c: number[], 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);
}
function rrect(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();
}
// 주기 [초록, 노랑, 빨강] 프레임 수에서 프레임 f 의 신호 상태
function phaseAt(f: number, g: number, y: number, r: number): number {
const total = g + y + r;
const m = ((f % total) + total) % total;
return m < g ? SIG_GREEN : (m < g + y ? SIG_YELLOW : SIG_RED);
}
function stateText(state: number): string {
return state === SIG_GREEN ? TXT_GO : (state === SIG_YELLOW ? TXT_READY : TXT_STOP);
}
// 신호 상태 -> 빨강·노랑·초록 렌즈 밝기 (위에서 아래)
function litOf(state: number): number[] {
return [state === SIG_RED ? 1 : 0, state === SIG_YELLOW ? 1 : 0, state === SIG_GREEN ? 1 : 0];
}
const LENS_RGBS = [RED_RGB, YELLOW_RGB, GREEN_RGB];
// 세로 신호등 머리 — 렌즈 세 개와 켜진 렌즈의 빛 번짐
function drawHead(ctx: CanvasRenderingContext2D, cx: number, cy: number, r: number, lit: number[]): void {
const step = r * 2.5;
rrect(ctx, cx - r * 1.45, cy - step - r * 1.45, r * 2.9, step * 2 + r * 2.9, r * 0.9);
ctx.fillStyle = rgba(INK_RGB, 1);
ctx.fill();
for (let i = 0; i < 3; i += 1) {
const ly = cy + (i - 1) * step;
ctx.beginPath();
ctx.arc(cx, ly, r, 0, PI2);
ctx.fillStyle = rgba(LENS_RGBS[i], 0.2 + 0.8 * lit[i]);
ctx.fill();
if (lit[i] > 0.02) {
glow(ctx, cx, ly, r * 3.2, LENS_RGBS[i], 0.55 * lit[i]);
}
}
}
// 위에서 본 차 — 앞 범퍼가 x, 가운데가 y. 제동 중이면 뒷등이 켜진다
function drawCar(ctx: CanvasRenderingContext2D, x: number, y: number, len: number, wid: number, rgb: number[], braking: boolean): void {
const x0 = x - len;
rrect(ctx, x0, y - wid / 2, len, wid, 6);
ctx.fillStyle = rgba(rgb, 1);
ctx.fill();
rrect(ctx, x - len * 0.62, y - wid / 2 + 3, len * 0.34, wid - 6, 3);
ctx.fillStyle = 'rgba(255,255,255,0.62)';
ctx.fill();
ctx.fillStyle = 'rgba(255,248,214,1)';
ctx.fillRect(x - 3, y - wid / 2 + 2, 3, 4);
ctx.fillRect(x - 3, y + wid / 2 - 6, 3, 4);
ctx.fillStyle = braking ? rgba(RED_RGB, 1) : 'rgba(150,120,150,0.8)';
ctx.fillRect(x0, y - wid / 2 + 2, 3, 4);
ctx.fillRect(x0, y + wid / 2 - 6, 3, 4);
if (braking) {
glow(ctx, x0, y, 12, RED_RGB, 0.45);
}
}
// 한 줄 도로 장면의 바탕 — 잔디 위에 도로띠 하나, 정지선과 횡단보도
function drawLaneBackdrop(ctx: CanvasRenderingContext2D, roadY: number, roadH: number, stopX: number, seedTrees: number): void {
ctx.fillStyle = rgba(GRASS_RGB, 1);
ctx.fillRect(0, 0, W, H);
const rnd = mulberry32(seedTrees);
for (let i = 0; i < 14; i += 1) {
const tx = 16 + rnd() * (W - 32);
const up = rnd() < 0.5;
const ty = up ? roadY - roadH / 2 - 22 - rnd() * 26 : roadY + roadH / 2 + 22 + rnd() * 26;
ctx.beginPath();
ctx.arc(tx, ty, 9 + rnd() * 6, 0, PI2);
ctx.fillStyle = 'rgba(160,214,184,0.9)';
ctx.fill();
}
ctx.fillStyle = rgba(ROAD_RGB, 1);
ctx.fillRect(0, roadY - roadH / 2, W, roadH);
ctx.fillStyle = rgba(ROAD_EDGE_RGB, 1);
ctx.fillRect(0, roadY - roadH / 2, W, 2);
ctx.fillRect(0, roadY + roadH / 2 - 2, W, 2);
ctx.fillStyle = rgba(MARK_RGB, 0.8);
for (let x = 6; x < W; x += 36) {
ctx.fillRect(x, roadY - 1, 18, 2);
}
for (let k = 0; k < 5; k += 1) {
ctx.fillRect(stopX + 5, roadY - roadH / 2 + 3 + k * (roadH - 6) / 5, 12, (roadH - 6) / 5 - 3);
}
ctx.fillRect(stopX - 2, roadY - roadH / 2, 3, roadH);
}
interface Car { x: number; v: number; len: number; rgb: number[]; go: boolean; decided: boolean; sigK: number; brake: boolean; id: number; }
interface Sig { x: number; state: number; }
interface LaneParams { accel: number; brake: number; gap: number; lineGap: number; vmax: number; headway: number; delta: number; len: number; }
// 한 줄 차량 흐름 — 앞차 간격(IDM)과 정지선을 같은 식으로 다룬다. 차는 앞쪽부터 0번이다
class Lane {
cars: Car[] = [];
p: LaneParams;
rnd: () => number;
nextAt = 0;
made = 0;
constructor(seed: number, p: LaneParams) {
this.p = p;
this.rnd = mulberry32(seed);
}
accelFor(v: number, s: number, vL: number, g0: number): number {
const p = this.p;
const sStar = g0 + Math.max(0, v * p.headway + v * (v - vL) / (2 * Math.sqrt(p.accel * p.brake)));
return p.accel * (1 - Math.pow(v / p.vmax, p.delta) - Math.pow(sStar / Math.max(s, 0.5), 2));
}
// f 프레임에, 뒤쪽이 비어 있고 때가 됐으면 한 대 들여보낸다
maybeSpawn(f: number, minGap: number, maxGap: number, v0: number): boolean {
if (f < this.nextAt) { return false; }
const last = this.cars.length > 0 ? this.cars[this.cars.length - 1] : null;
if (last && last.x - last.len < this.p.gap + 10) { return false; }
const rgb = CAR_RGBS[this.made % CAR_RGBS.length];
this.cars.push({ x: -2, v: v0, len: this.p.len, rgb: rgb, go: false, decided: false, sigK: -1, brake: false, id: this.made });
this.made += 1;
this.nextAt = f + minGap + Math.floor(this.rnd() * (maxGap - minGap + 1));
return true;
}
// 신호 목록은 x 오름차순. 한 번 호출 = 한 프레임. 정지선을 넘은 차(detect 용) id 를 돌려준다
step(sigs: Sig[], onCross: (c: Car, x: number) => void, watchX: number): void {
const p = this.p;
for (let i = 0; i < this.cars.length; i += 1) {
const c = this.cars[i];
let acc = this.accelFor(c.v, 1e6, c.v, p.gap);
if (i > 0) {
const L = this.cars[i - 1];
acc = Math.min(acc, this.accelFor(c.v, (L.x - L.len) - c.x, L.v, p.gap));
}
let k = -1;
for (let j = 0; j < sigs.length; j += 1) {
if (sigs[j].x >= c.x) { k = j; break; }
}
let clampX = 1e9;
if (k >= 0) {
const sg = sigs[k];
if (c.sigK !== k) { c.sigK = k; c.decided = false; c.go = false; }
if (sg.state === SIG_GREEN) {
c.decided = false;
c.go = false;
} else {
if (!c.decided) {
c.decided = true;
c.go = c.v * c.v / (2 * p.brake) > sg.x - c.x;
}
if (!c.go) {
acc = Math.min(acc, this.accelFor(c.v, sg.x - c.x - 2, 0, p.lineGap));
clampX = sg.x - 1.5;
}
}
}
acc = Math.max(acc, -p.brake * 3);
const prevX = c.x;
c.v = Math.max(0, c.v + acc);
c.x += c.v;
if (c.x > clampX && prevX <= clampX) {
c.x = clampX;
c.v = 0;
}
c.brake = acc < -0.012 || c.v < 0.05;
if (prevX < watchX && c.x >= watchX) { onCross(c, watchX); }
}
while (this.cars.length > 0 && this.cars[0].x - this.cars[0].len > W + 20) {
this.cars.shift();
}
}
// 정지선 뒤에서 서 있는 차 수
waiting(stopX: number): number {
let n = 0;
for (let i = 0; i < this.cars.length; i += 1) {
const c = this.cars[i];
if (c.v < 0.25 && c.x < stopX + 2 && c.x > stopX - 260) { n += 1; }
}
return n;
}
}
function main(rootEl: HTMLElement, canvas: HTMLCanvasElement, statusEl: HTMLElement, btnEl: HTMLButtonElement): () => void {
const ctx0 = canvas.getContext('2d');
if (!ctx0) { return function (): void { return; }; }
canvas.width = W;
canvas.height = H;
const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
const scene = makeScene(ctx0, reduce);
if (reduce) { rootEl.classList.remove('is-demo'); }
let paused = false;
let rafId = 0;
let lastTs: number | null = null;
let accMs = 0;
let lastLabel = '';
let px = W / 2;
let py = H / 2;
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();
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) { scene.step(); }
}
function setButton(): void {
btnEl.textContent = reduce ? '다음 장면' : (paused ? '재생' : '멈춤');
}
function toLocal(e: PointerEvent): Pt {
const r = canvas.getBoundingClientRect();
return [clamp((e.clientX - r.left) * W / r.width, 0, W), clamp((e.clientY - r.top) * H / r.height, 0, H)];
}
function moved(): void {
if (scene.point) { scene.point(px, py); }
if (reduce) { show(); }
}
function onButton(): void {
if (reduce) {
advance(REDUCE_STEP_MS);
show();
return;
}
paused = !paused;
if (paused) { rootEl.classList.remove('is-demo'); } else { rootEl.classList.add('is-demo'); }
setButton();
}
function onAction(): void {
if (scene.tap) {
scene.tap();
if (reduce) { show(); }
return;
}
onButton();
}
function tick(ts: number): void {
if (lastTs === null) { lastTs = ts; }
const frameDt = Math.min(ts - lastTs, 160);
lastTs = ts;
if (!paused) {
accMs += frameDt;
while (accMs >= FIXED_DT) {
scene.step();
accMs -= FIXED_DT;
}
show();
}
rafId = requestAnimationFrame(tick);
}
listen(btnEl, 'click', function (): void { onButton(); });
listen(canvas, 'pointerdown', function (e: Event): void {
const p = toLocal(e as PointerEvent);
px = p[0];
py = p[1];
moved();
if (scene.tap) {
scene.tap();
if (reduce) { show(); }
}
});
listen(canvas, 'pointermove', function (e: Event): void {
const p = toLocal(e as PointerEvent);
px = p[0];
py = p[1];
moved();
});
listen(canvas, 'keydown', function (e: Event): void {
const k = (e as KeyboardEvent).key;
if (k === 'Enter' || k === ' ') {
e.preventDefault();
onAction();
return;
}
let dx = 0;
let dy = 0;
if (k === 'ArrowLeft') { dx = -KEY_STEP; } else if (k === 'ArrowRight') { dx = KEY_STEP; }
else if (k === 'ArrowUp') { dy = -KEY_STEP; } else if (k === 'ArrowDown') { dy = KEY_STEP; }
else { return; }
e.preventDefault();
px = clamp(px + dx, 0, W);
py = clamp(py + dy, 0, H);
moved();
});
advance(REDUCE_START_MS);
setButton();
show();
if (!reduce) {
rafId = requestAnimationFrame(tick);
}
function destroy(): void {
cancelAnimationFrame(rafId);
for (let i = 0; i < cleaners.length; i += 1) { cleaners[i](); }
}
return destroy;
}
const SAFE_GAP = 24;
const BRAKE_DECEL = 0.07;
const ACCEL = 0.04;
const STOP_LINE_X = 372;
const ROAD_Y = 150;
const ROAD_H = 80;
const CAR_LEN = 46;
const CAR_WID = 30;
const GREEN_LEN = 84;
const YELLOW_LEN = 26;
const RED_LEN = 100;
const FREE_SPEED = 2.2;
const HEADWAY = 10;
const SEED = 446;
function makeScene(ctx: CanvasRenderingContext2D, reduce: boolean): Scene {
const lane = new Lane(SEED, { accel: ACCEL, brake: BRAKE_DECEL, gap: SAFE_GAP, lineGap: 3, vmax: FREE_SPEED, headway: HEADWAY, delta: 4, len: CAR_LEN });
const sig: Sig = { x: STOP_LINE_X, state: SIG_GREEN };
const sigs: Sig[] = [sig];
const cycle = GREEN_LEN + YELLOW_LEN + RED_LEN;
let f = GREEN_LEN - 24;
let skew = 0;
function tickSignal(): void {
sig.state = phaseAt(f + skew, GREEN_LEN, YELLOW_LEN, RED_LEN);
}
function none(c: Car, x: number): void { return; }
const scene: Scene = {
step: function (): void {
f += 1;
tickSignal();
lane.maybeSpawn(f, 30, 56, FREE_SPEED * 0.9);
lane.step(sigs, none, -1);
},
// 누르면 신호가 지금 상태에서 바로 다음 단계로 넘어간다
tap: function (): void {
const m = (((f + skew) % cycle) + cycle) % cycle;
const target = sig.state === SIG_RED ? 0 : (sig.state === SIG_GREEN ? GREEN_LEN : GREEN_LEN + YELLOW_LEN);
skew += ((target - m) % cycle + cycle) % cycle;
tickSignal();
},
label: function (): string { return stateText(sig.state); },
draw: function (): void {
drawLaneBackdrop(ctx, ROAD_Y, ROAD_H, STOP_LINE_X, 17);
for (let i = 0; i < lane.cars.length; i += 1) {
const c = lane.cars[i];
drawCar(ctx, c.x, ROAD_Y, c.len, CAR_WID, c.rgb, c.brake);
}
// 서 있는 차 사이 간격 — 앞차 뒤꽁무니와 내 앞 범퍼 사이를 칠하고 폭을 적는다
ctx.strokeStyle = rgba(INK_RGB, 0.8);
ctx.lineWidth = 1.5;
ctx.fillStyle = rgba(INK_RGB, 0.9);
ctx.font = '500 10px ' + FONT;
ctx.textAlign = 'center';
for (let i = 1; i < lane.cars.length; i += 1) {
const c = lane.cars[i];
const L = lane.cars[i - 1];
if (c.v < 0.25 && L.v < 0.25) {
const a = c.x;
const b = L.x - L.len;
ctx.fillStyle = rgba(YELLOW_RGB, 0.55);
ctx.fillRect(a, ROAD_Y - CAR_WID / 2, b - a, CAR_WID);
ctx.fillStyle = rgba(INK_RGB, 0.9);
ctx.beginPath();
ctx.moveTo(a, ROAD_Y + CAR_WID / 2 + 7);
ctx.lineTo(b, ROAD_Y + CAR_WID / 2 + 7);
ctx.moveTo(a, ROAD_Y + CAR_WID / 2 + 3);
ctx.lineTo(a, ROAD_Y + CAR_WID / 2 + 11);
ctx.moveTo(b, ROAD_Y + CAR_WID / 2 + 3);
ctx.lineTo(b, ROAD_Y + CAR_WID / 2 + 11);
ctx.stroke();
ctx.fillText(String(Math.round(b - a)), (a + b) / 2, ROAD_Y + CAR_WID / 2 + 22);
}
}
// 신호 — 정지선 위쪽
drawHead(ctx, STOP_LINE_X + 20, ROAD_Y - ROAD_H / 2 - 40, 8, litOf(sig.state));
ctx.fillStyle = rgba(INK_RGB, 1);
ctx.fillRect(STOP_LINE_X + 18, ROAD_Y - ROAD_H / 2 - 8, 4, 8);
}
};
if (reduce) { tickSignal(); }
for (let i = 0; i < 330; i += 1) { scene.step(); }
return scene;
}
export default function TlCarFollowStopLineGap() {
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 main(root, canvas, statusEl, btnEl);
}, []);
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="빨간불에 앞차 뒤로 간격을 두고 서는 차들" />
<p className={styles.sc__status} ref={statusRef} aria-live="polite">초록불 — 진행</p>
<button className={styles.sc__btn} ref={btnRef} type="button">멈춤</button>
<p className={styles.sc__caption}>빨간불에 앞차 뒤로 간격을 두고 서는 차들</p>
</div>
</main>
);
}02 Cars That Stop Behind the Car Ahead With a Gap at Red — Measured area 10.192% · moving frames 23/23Original by GODRICH · SCSS and React ship in the zip · Traffic Light CSS: 9 Demos With Queues and Waves
The post this demo lives in
Traffic Light CSS: 9 Demos With Queues and WavesA traffic light css built as a color-swapping timer lets cars roll through red, signals drift out of step and pedestrian See all demos in this post
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