Animating multiple circles in a canvas



I’m trying to make an animation inside a canvas: here, a numbered circle must be drawn and move from left to right one single time, disappearing as soon as it reaches the end of animation.

For now I managed to animate it in loop, but I need to animate at the same time (or with a set delay) multiple numbered circles, strating in different rows (changing y position) so they wont overlap.

Any idea how can I manage this? my JS code is the following:

// Single Animated Circle - Get Canvas element by Id
var canvas = document.getElementById("canvas");

// Set Canvas dimensions
canvas.width = 300;
canvas.height = 900;

// Get drawing context
var ctx = canvas.getContext("2d");

// Radius
var radius = 13;
// Starting Position
var x = radius;
var y = radius;

// Speed in x and y direction
var dx = 1;
var dy = 0;

// Generate random number
var randomNumber = Math.floor(Math.random() * 60) + 1;

if (randomNumber > 0 && randomNumber <= 10) {
  ctx.strokeStyle = "#0b0bf1";
} else if (randomNumber > 10 && randomNumber <= 20) {
  ctx.strokeStyle = "#f10b0b";
} else if (randomNumber > 20 && randomNumber <= 30) {
  ctx.strokeStyle = "#0bf163";
} else if (randomNumber > 30 && randomNumber <= 40) {
  ctx.strokeStyle = "#f1da0b";
} else if (randomNumber > 40 && randomNumber <= 50) {
  ctx.strokeStyle = "#950bf1";
} else if (randomNumber > 50 && randomNumber <= 60) {
  ctx.strokeStyle = "#0bf1e5";
}

function animate3() {
  requestAnimationFrame(animate3);

  ctx.clearRect(0, 0, 300, 900);

  if (x + radius > 300 || x - radius < 0) {
    x = radius;
  }

  x += dx;

  ctx.beginPath();
  ctx.arc(x, y, 12, 0, Math.PI * 2, false);
  ctx.stroke();
  ctx.fillText(randomNumber, x - 5, y + 3);
}

// Animate the Circle

animate3();
<canvas id="canvas"></canvas>

Answer

Here is a solution which doesn’t use classes as such and separates the animation logic from the updating – which can be useful if you want more precise control over timing.

// Some helper functions
const clamp = (number, min, max) => Math.min(Math.max(number, min), max);

// Choose and remove random member of arr with equal probability 
const takeRandom = arr => arr.splice(parseInt(Math.random() * arr.length), 1)[0]

// Call a function at an interval, passing the amount of time that has passed since the last call
function update(callBack, interval) {
  let now = performance.now();
  let last;
  setInterval(function() {
    last = now;
    now = performance.now();
    callBack((now - last) / 1000);
  })
}

const settings = {
  width: 300,
  height: 150,
  radius: 13,
  gap: 5,
  circles: 5,
  maxSpeed: 100,
  colors: ["#0b0bf1", "#f10b0b", "#0bf163", "#f1da0b", "#950bf1", "#0bf1e5"]
};
const canvas = document.getElementById("canvas");
canvas.width = settings.width;
canvas.height = settings.height;
const ctx = canvas.getContext("2d");

// Set circle properties
const circles = [...Array(settings.circles).keys()].map(i => ({
  number: i + 1,
  x: settings.radius,
  y: settings.radius + (settings.radius * 2 + settings.gap) * i,
  radius: settings.radius,
  dx: settings.maxSpeed * Math.random(), // This is the speed in pixels per second
  dy: 0,
  color: takeRandom(settings.colors)
}));

function drawCircle(circle) {
  ctx.strokeStyle = circle.color;
  ctx.beginPath();
  ctx.arc(circle.x, circle.y, circle.radius, 0, Math.PI * 2, false);
  ctx.stroke();
  ctx.fillText(circle.number, circle.x - 5, circle.y + 3);
}

function updateCircle(circle, dt) {
  // Update a circle's position after dt seconds
  circle.x = clamp(circle.x + circle.dx * dt, circle.radius + 1, settings.width - circle.radius - 1);
  circle.y = clamp(circle.y + circle.dy * dt, circle.radius + 1, settings.height - circle.radius - 1);
}

function animate() {
  ctx.clearRect(0, 0, settings.width, settings.height);
  circles.forEach(drawCircle);
  requestAnimationFrame(animate);
}

update(dt => circles.forEach(circle => updateCircle(circle, dt)), 50);
animate();
<canvas id="canvas" style="border: solid 1px black"></canvas>


Source: stackoverflow