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const NUM_POINTS = 5;
// thanks vihart
const TAU = 2 * Math.PI;
// no more than 1% of world size per tick.
const MAX_SPEED = 0.01;
// size of rendered points in proportion to canvas.
const POINT_RADIUS = 0.01;
class Point {
x = Math.random();
y = Math.random();
#heading = Math.random() * TAU;
speed = Math.random() * MAX_SPEED;
color = randColor();
#speedX;
get speedX() {
if (this.#speedX === undefined) {
this.#speedX = this.speed * Math.cos(this.heading);
}
return this.#speedX;
}
#speedY;
get speedY() {
if (this.#speedY === undefined) {
this.#speedY = this.speed * Math.sin(this.heading);
}
return this.#speedY;
}
get heading() {
return this.#heading;
}
set heading(val) {
this.#heading = val;
this.#speedX = this.#speedY = undefined;
}
}
const points = [...Array(NUM_POINTS)].map(_ => new Point());
function randColor() {
const [r, g, b] = [...Array(3)].map(_ => Math.random() * 255);
return `rgb(${r} ${g} ${b})`
}
function renderPoints(ctx, points) {
points.forEach(p => {
ctx.fillStyle = p.color;
ctx.beginPath();
ctx.arc(p.x, p.y, POINT_RADIUS, 0, TAU);
ctx.fill();
ctx.lineWidth = 0.005;
ctx.beginPath();
ctx.moveTo(p.x, p.y);
ctx.lineTo(p.x + p.speedX * 3, p.y + p.speedY * 3);
ctx.stroke();
});
}
function movePoints(points) {
points.forEach(p => {
p.x += p.speedX;
p.y += p.speedY;
});
}
function bouncePoints(points) {
let didBounce = false;
points.forEach(p => {
const x = p.x + p.speedX;
const y = p.y + p.speedY;
if (x < 0) {
p.heading = Math.PI - p.heading;
didBounce = true;
} else if (x >= 1) {
p.heading = Math.PI - p.heading;
didBounce = true;
} else if (y < 0) {
p.heading = -1 * p.heading;
didBounce = true;
} else if (y >= 1) {
p.heading = -1 * p.heading;
didBounce = true;
}
});
return didBounce;
}
async function loaded() {
const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');
console.debug('canvas:', canvas, 'ctx', ctx, 'points:', points);
ctx.scale(canvas.width, canvas.height);
const fps = document.querySelector('#fps');
const goButton = document.querySelector('button');
let paused = true;
goButton.onclick = e => {
paused = !paused;
if (paused) {
e.target.textContent = 'go';
} else {
e.target.textContent = 'pause';
self.requestAnimationFrame(render);
}
};
let lastTime = document.timeline.currentTime;
function render(t) {
if (t > lastTime) {
fps.textContent = Math.floor(1_000 / (t - lastTime));
lastTime = t;
}
ctx.clearRect(0, 0, canvas.width, canvas.height);
renderPoints(ctx, points);
if (bouncePoints(points)) {
//goButton.onclick({ target: goButton });
}
movePoints(points);
if (!paused) {
self.requestAnimationFrame(render);
}
}
//goButton.onclick({ target: goButton });
render(document.timeline.currentTime);
}
document.addEventListener('DOMContentLoaded', loaded);
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