HTML Canvas Graphics

The HTML <canvas> element is used to draw graphics on a web page.

What is HTML Canvas?

The HTML <canvas> 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.

Canvas has several methods for drawing paths, boxes, circles, text, and adding images.

Canvas Examples

A canvas is a rectangular area on an HTML page. By default, a canvas has no border and no content.

The markup looks like this:

<canvas id="myCanvas" width="300" height="100"></canvas>

note

Always specify an id attribute (to be referred to in a script), and a width and height attribute to define the size of the canvas. To add a border, use the style attribute.

Example of an empty canvas:

<canvas id="myCanvas" width="200" height="100" style="border:1px solid #000000;">  
</canvas>

note

Coordinates (0,0) defines the upper left corner of the canvas.

Output:

Add JavaScript code

After creating the rectangular canvas area, you must add JavaScript code to do the drawing.

Here are some examples.

Draw a Line

If you want to draw a straight line on the canvas, you can use the following two methods:

• moveTo(x,y): It is used to define the starting point of the line.

• lineTo(x,y): It is used to define the ending point of the line.

If you draw a line which starting point is (0,0) and the end point is (200,100), use the stroke method to draw the line.

<script>  
	var c = document.getElementById("myCanvas");  
	var cctx = c.getContext("2d");  
	ctx.moveTo(0,0);  
	ctx.lineTo(200,100);  
	ctx.stroke();  
</script>  

Output:

Draw a Circle

If you want to draw a circle on the canvas, you can use the arc() method:

arc(x, y, r, start, stop)

To sketch circle on HTML canvas, use one of the ink() methods, like stroke() or fill().

<script>  
	var c = document.getElementById("myCanvas");  
	var cctx = c.getContext("2d");  
	ctx.beginPath();  
	ctx.arc(95,50,40,0,2*Math.PI);  
	ctx.stroke();  
</script>  

Output:

Draw a Text

There are property and methods used for drawing text on the canvas.

• font property: It is used to define the font property for the text.
• fillText(text,x,y) method: It is used to draw filled text on the canvas. It looks like bold font.
• strokeText(text,x,y) method: It is also used to draw text on the canvas, but the text is unfilled.

Let's see fillText() method example.

<script>  
	var c = document.getElementById("myCanvas");  
	var cctx = c.getContext("2d");  
	ctx.font = "30px Arial";  
	ctx.fillText("Hello World",10,50);  
</script>  

Output:

Let's see strokeText() method example.

<script>  
	var c = document.getElementById("myCanvas");  
	var cctx = c.getContext("2d");  
	ctx.font = "30px Arial";  
	ctx.strokeText("Hello World",10,50);  
</script>  

Output:

Draw Linear Gradient

<script>  
	var c = document.getElementById("myCanvas");  
	var ctx = c.getContext("2d");  
	  
	// Create gradient  
	var grd = ctx.createLinearGradient(0, 0, 200, 0);  
	grd.addColorStop(0, "red");  
	grd.addColorStop(1, "white");  
	  
	// Fill with gradient  
	ctx.fillStyle = grd;  
	ctx.fillRect(10, 10, 150, 80);  
</script>

Output:

Draw Circular Gradient

<script>  
	var c = document.getElementById("myCanvas");  
	var ctx = c.getContext("2d");  
	  
	// Create gradient  
	var grd = ctx.createRadialGradient(75, 50, 5, 90, 60, 100);  
	grd.addColorStop(0, "red");  
	grd.addColorStop(1, "white");  
	  
	// Fill with gradient  
	ctx.fillStyle = grd;  
	ctx.fillRect(10, 10, 150, 80);  
</script>

Output: