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How to draw animated circles in HTML5 canvas

Step 1 - Draw Circle

Step 2 - Draw multiple circles

Step 3 - Animate one circle

Step 4 - Animate multiple circles

Step 5 - Add colors to Animated Circles

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You can draw animated circles in an HTML5 canvas using JavaScript by leveraging the requestAnimationFrame function. Below is a step-by-step guide to animating circles using the Canvas API.

Step 1: Create an HTML5 Canvas

First, create an HTML file with a <canvas> element:


<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Animated Circles</title>
    <style>
        body {
            display: flex;
            justify-content: center;
            align-items: center;
            height: 100vh;
            margin: 0;
            background-color: black;
        }
        canvas {
            border: 1px solid white;
        }
    </style>
</head>
<body>
    <canvas id="canvas"></canvas>
    <script src="script.js"></script>
</body>
</html>

Step 2: JavaScript Code to Animate Circles

Create a script.js file with the following logic:


const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");

// Set canvas size to full window
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

// Circle properties
const circles = [];
const numCircles = 10;

// Function to generate random values
function random(min, max) {
    return Math.random() * (max - min) + min;
}

// Circle class
class Circle {
    constructor(x, y, radius, dx, dy, color) {
        this.x = x;
        this.y = y;
        this.radius = radius;
        this.dx = dx; // X velocity
        this.dy = dy; // Y velocity
        this.color = color;
    }

    draw() {
        ctx.beginPath();
        ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false);
        ctx.fillStyle = this.color;
        ctx.fill();
        ctx.closePath();
    }

    update() {
        // Bounce off walls
        if (this.x + this.radius > canvas.width || this.x - this.radius < 0) {
            this.dx = -this.dx;
        }
        if (this.y + this.radius > canvas.height || this.y - this.radius < 0) {
            this.dy = -this.dy;
        }

        // Move circle
        this.x += this.dx;
        this.y += this.dy;

        this.draw();
    }
}

// Create multiple circles
for (let i = 0; i < numCircles; i++) {
    let radius = random(10, 40);
    let x = random(radius, canvas.width - radius);
    let y = random(radius, canvas.height - radius);
    let dx = random(-2, 2);
    let dy = random(-2, 2);
    let color = `hsl(${random(0, 360)}, 100%, 50%)`;

    circles.push(new Circle(x, y, radius, dx, dy, color));
}

// Animation loop
function animate() {
    ctx.clearRect(0, 0, canvas.width, canvas.height); // Clear canvas
    circles.forEach(circle => circle.update()); // Update circles
    requestAnimationFrame(animate);
}

// Start animation
animate();

How It Works

  1. Canvas Setup: The canvas fills the entire window.
  2. Circle Class:
    • Each circle has a random position, size, speed, and color.
    • The draw() method renders the circle.
    • The update() method updates its position and bounces it off walls.
  3. Animation Loop:
    • Clears the canvas.
    • Moves each circle.
    • Calls requestAnimationFrame(animate) for smooth animation.

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