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HTML5 Canvas

The <canvas> element is used to draw graphics, on the fly, on a web page.

Draw a red rectangle, a gradient rectangle, a multicolor rectangle, and some multicolor text onto the canvas:

What is Canvas?

The HTML5 <canvas> element is used to draw graphics, on the fly, via scripting (usually JavaScript).

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

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

Browser Support

Internet Explorer 9+, Firefox, Opera, Chrome, and Safari support the <canvas> element.

Note: Internet Explorer 8 and earlier versions, do not support the <canvas> element.

Create a Canvas

A canvas is a rectangular area on an HTML page, and it is specified with the <canvas> element.

Note: By default, the <canvas> element has no border and no content.

The markup looks like this:

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.

Tip: You can have multiple <canvas> elements on one HTML page.

To add a border, use the style attribute:

Draw Onto The Canvas With JavaScript

All drawing on the canvas must be done inside a JavaScript:

Example explained:

First, find the <canvas> element:

Then, call its getContext() method (you must pass the string "2d" to the getContext() method):

The getContext("2d") object is a built-in HTML5 object, with many properties and methods for drawing paths, boxes, circles, text, images, and more.

The next two lines draw a red rectangle:

The fillStyle property can be a CSS color, a gradient, or a pattern. The default fillStyle is #000000 (black).

The fillRect(x,y,width,height) method draws a rectangle filled with the current fill style.

Canvas Coordinates

The canvas is a two-dimensional grid.

The upper-left corner of the canvas has coordinate (0,0)

So, the fillRect() method above had the parameters (0,0,150,75).

This means: Start at the upper-left corner (0,0) and draw a 150x75 pixels rectangle.

Coordinates Example

Mouse over the rectangle below to see its x and y coordinates:

Canvas - Paths

To draw straight lines on a canvas, we will use the following two methods:

• moveTo(x,y) defines the starting point of the line
• lineTo(x,y) defines the ending point of the line

To actually draw the line, we must use one of the "ink" methods, like stroke().

To draw a circle on a canvas, we will use the following method:

• arc(x,y,r,start,stop)

To actually draw the circle, we must use one of the "ink" methods, like stroke() or fill().

Canvas - Text

To draw text on a canvas, the most important property and methods are:

• font - defines the font properties for text
• fillText(text,x,y) - Draws "filled" text on the canvas
• strokeText(text,x,y) - Draws text on the canvas (no fill)

Using fillText():

Using strokeText():

Canvas - Gradients

Gradients can be used to fill rectangles, circles, lines, text, etc. Shapes on the canvas are not limited to solid colors.

There are two different types of gradients:

• createLinearGradient(x,y,x1,y1) - Creates a linear gradient
• createRadialGradient(x,y,r,x1,y1,r1) - Creates a radial/circular gradient

Once we have a gradient object, we must add two or more color stops.

The addColorStop() method specifies the color stops, and its position along the gradient. Gradient positions can be anywhere between 0 to 1.

To use the gradient, set the fillStyle or strokeStyle property to the gradient, and then draw the shape, like a rectangle, text, or a line.

Using createLinearGradient():

Using createRadialGradient():

Canvas - Images

To draw an image on a canvas, we will use the following method:

• drawImage(image,x,y)

HTML Canvas Reference

For a complete reference of all the properties and methods that can be used with the Canvas object (with try-it examples on every property and method), go to our Canvas Reference.

The HTML <canvas> Tag