HTML Canvas

HTML5 <canvas> provides a powerful way to create dynamic, interactive animations using JavaScript. In this tutorial, you’ll learn the basics of animating objects, combining movements, and creating visually appealing effects.

What You’ll Learn

1. The core concepts of canvas animation.
2. Moving objects with the animation loop.
3. Creating smooth transitions using requestAnimationFrame.
4. Combining movements and adding interactivity.
5. Practical animation examples.

1. Basics of Canvas Animations

Canvas animations involve:

1. Clearing the canvas: To redraw the frame.
2. Drawing objects: Define what needs to be animated.
3. Updating object properties: Adjust the position, size, or other attributes.
4. Repeating the process: Use requestAnimationFrame to create the animation loop.

2. Setting Up the Canvas

Example 1: Setting Up the Canvas

<canvas id="myCanvas" width="500" height="300" style="border: 1px solid black;"></canvas>
<script>
    const canvas = document.getElementById("myCanvas");
    const ctx = canvas.getContext("2d");
</script>

3. Creating a Moving Object

Example 2: Moving a Circle Horizontally

let x = 0; // Initial x-coordinate
const radius = 20;

function draw() {
    ctx.clearRect(0, 0, canvas.width, canvas.height); // Clear the canvas

    // Draw the circle
    ctx.beginPath();
    ctx.arc(x, canvas.height / 2, radius, 0, Math.PI * 2);
    ctx.fillStyle = "blue";
    ctx.fill();
    ctx.closePath();

    // Update the position
    x += 2;
    if (x - radius > canvas.width) {
        x = -radius; // Reset when off-screen
    }

    requestAnimationFrame(draw); // Repeat the animation
}

draw();

Explanation:

• clearRect: Clears the canvas before each frame.
• requestAnimationFrame: Schedules the next frame for smooth animation.

4. Adding Vertical Movement

You can add vertical movement by updating the Y-coordinate.

Example 3: Bouncing Ball

let x = 100;
let y = 50;
let dx = 2; // Change in x
let dy = 2; // Change in y
const radius = 20;

function draw() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);

    // Draw the ball
    ctx.beginPath();
    ctx.arc(x, y, radius, 0, Math.PI * 2);
    ctx.fillStyle = "red";
    ctx.fill();
    ctx.closePath();

    // Update position
    x += dx;
    y += dy;

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

    requestAnimationFrame(draw);
}

draw();

5. Animating Multiple Objects

Example 4: Moving Multiple Balls

const balls = [
    { x: 50, y: 60, dx: 2, dy: 1, color: "blue" },
    { x: 200, y: 100, dx: -1.5, dy: 2, color: "green" },
    { x: 300, y: 50, dx: 2, dy: -2, color: "orange" }
];

function drawBalls() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);

    balls.forEach((ball) => {
        // Draw each ball
        ctx.beginPath();
        ctx.arc(ball.x, ball.y, radius, 0, Math.PI * 2);
        ctx.fillStyle = ball.color;
        ctx.fill();
        ctx.closePath();

        // Update position
        ball.x += ball.dx;
        ball.y += ball.dy;

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

    requestAnimationFrame(drawBalls);
}

drawBalls();

6. Adding Easing and Smooth Transitions

Example 5: Easing Animation

let targetX = 400; // Target position
let x = 0; // Current position

function easeAnimation() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);

    // Draw the object
    ctx.beginPath();
    ctx.arc(x, canvas.height / 2, radius, 0, Math.PI * 2);
    ctx.fillStyle = "purple";
    ctx.fill();
    ctx.closePath();

    // Update position (easing)
    x += (targetX - x) * 0.05; // Move closer to the target

    requestAnimationFrame(easeAnimation);
}

easeAnimation();

Explanation:

• The easing formula x += (targetX – x) * 0.05 creates a smooth transition by reducing the distance incrementally.

7. Adding Interactivity

Example 6: Interactive Animation (Follow Mouse)

let mouseX = 0;
let mouseY = 0;

canvas.addEventListener("mousemove", (event) => {
    const rect = canvas.getBoundingClientRect();
    mouseX = event.clientX - rect.left;
    mouseY = event.clientY - rect.top;
});

function followMouse() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);

    // Draw a circle at the mouse position
    ctx.beginPath();
    ctx.arc(mouseX, mouseY, radius, 0, Math.PI * 2);
    ctx.fillStyle = "orange";
    ctx.fill();
    ctx.closePath();

    requestAnimationFrame(followMouse);
}

followMouse();

8. Practical Example: Animated Scene

Example 7: A Simple Solar System

let angle = 0;

function drawSolarSystem() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);

    // Draw the sun
    ctx.beginPath();
    ctx.arc(250, 150, 30, 0, Math.PI * 2);
    ctx.fillStyle = "yellow";
    ctx.fill();
    ctx.closePath();

    // Draw the earth orbit
    const earthX = 250 + Math.cos(angle) * 100;
    const earthY = 150 + Math.sin(angle) * 100;

    ctx.beginPath();
    ctx.arc(earthX, earthY, 15, 0, Math.PI * 2);
    ctx.fillStyle = "blue";
    ctx.fill();
    ctx.closePath();

    // Draw the moon orbiting the earth
    const moonX = earthX + Math.cos(angle * 4) * 30;
    const moonY = earthY + Math.sin(angle * 4) * 30;

    ctx.beginPath();
    ctx.arc(moonX, moonY, 5, 0, Math.PI * 2);
    ctx.fillStyle = "gray";
    ctx.fill();
    ctx.closePath();

    angle += 0.02; // Adjust speed

    requestAnimationFrame(drawSolarSystem);
}

drawSolarSystem();

9. Best Practices for Canvas Animations

1. Use requestAnimationFrame:
   • Provides smoother animations and optimizes performance.
2. Keep It Clean:
   • Always clear the canvas before redrawing.
3. Isolate Logic:
   • Use separate functions for drawing, updating, and handling user input.
4. Optimize Performance:
   • Minimize unnecessary calculations during each frame.

10. Browser Support

All modern browsers support canvas animations:

11. Conclusion

In this tutorial, you learned:

1. The basics of creating animations with HTML5 Canvas.
2. How to move, resize, and rotate objects dynamically.
3. How to create interactive animations and combine movements.