JavaScript Project - Drawing Application

 In this tutorial, we will learn how to create a simple JavaScript Drawing Application.

We will use the <canvas> HTML element to draw graphics on a web page.

The <canvas> HTML element is used to draw graphics, on the fly, via JavaScript.

The <canvas> element is only a container for graphics. You must use JavaScript to actually draw the graphics.

The <canvas> tag is a relatively new element that is quickly gaining in popularity. It can be used for a variety of different things, such as drawing graphs, shapes, images, applying styles and colors, making photo compositions, and even some simple, neat animations.

JavaScript Drawing Application

Create a folder called drawing-app as project workspace and we will create all the project files inside this folder.

1. index.html

Let's create index.html and add the following code to it:

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>Drawing App</title>
        <link rel="stylesheet" href="style.css" />
        <script src="script.js" defer></script>
    </head>
    <body>
		<h1> Drawing App </h1>
        <canvas id="canvas" width="800" height="400"></canvas>
        <div class="toolbox">
            <button id="decrease">-</button>
            <span id="size">30</span>
            <button id="increase">+</button>
            <input type="color" id="color" />
            <button id="clear">💩</button>
        </div>
    </body>
</html>

2. script.js

Let's create JavaScript file named script.js and add following JavaScript code to it:

const canvas = document.getElementById("canvas");
const increaseBtn = document.getElementById("increase");
const decreaseBtn = document.getElementById("decrease");
const sizeEl = document.getElementById("size");
const colorEl = document.getElementById("color");
const clearEl = document.getElementById("clear");
const ctx = canvas.getContext("2d");

let size = 30;
let isPressed = false;
let color = "black";
let x = undefined;
let y = undefined;

canvas.addEventListener("mousedown", (e) => {
    isPressed = true;

    x = e.offsetX;
    y = e.offsetY;
});

canvas.addEventListener("mouseup", (e) => {
    isPressed = false;

    x = undefined;
    y = undefined;
});

canvas.addEventListener("mousemove", (e) => {
    if (isPressed) {
        const x2 = e.offsetX;
        const y2 = e.offsetY;

        drawCircle(x2, y2);
        drawLine(x, y, x2, y2);
        x = x2;
        y = y2;
    }
});

function drawCircle(x, y) {
    ctx.beginPath();
    ctx.arc(x, y, size, 0, Math.PI * 2);
    ctx.fillStyle = color;
    ctx.fill();
}

function drawLine(x1, y1, x2, y2) {
    ctx.beginPath();
    ctx.moveTo(x1, y1);
    ctx.lineTo(x2, y2);
    ctx.strokeStyle = color;
    ctx.lineWidth = size * 2;
    ctx.stroke();
}

increaseBtn.addEventListener("click", () => {
    size += 5;

    if (size > 50) {
        size = 50;
    }

    updateSizeOnScreen();
});

decreaseBtn.addEventListener("click", () => {
    size -= 5;

    if (size < 5) {
        size = 5;
    }

    updateSizeOnScreen();
});

colorEl.addEventListener("change", (e) => {
    color = e.target.value;
});

clearEl.addEventListener("click", () => {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
});

function updateSizeOnScreen() {
    sizeEl.innerText = size;
}

style.css

Let's create CSS file named style.css and add the following CSS code to it:

@import url("https://fonts.googleapis.com/css2?family=Poppins:wght@200;400;600&display=swap");

* {
    box-sizing: border-box;
}

body {
    background-color: #f5f5f5;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    font-family: "Poppins", sans-serif;
    margin: 0;
    min-height: 100vh;
}

canvas {
    border: 2px solid rebeccapurple;
}

.toolbox {
    background-color: rebeccapurple;
    border: 1px solid rebeccapurple;
    display: flex;
    padding: 1rem;
    width: 804px;
}

.toolbox > * {
    background-color: #fff;
    border: none;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    padding: 0.25rem;
    margin: 0.25rem;
    height: 50px;
    width: 50px;
}

.toolbox > *:last-child {
    margin-left: auto;
}

Open index.html in Browser

Let's open the index.html file in the browser and you will be able to see the following screen:

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