<canvas> HTML graphics canvas element

Attributes

This element's attributes include the global attributes.

height

The height of the coordinate space in CSS pixels. Defaults to 150.

moz-opaque

Lets the canvas know whether translucency will be a factor. If the canvas knows there's no translucency, painting performance can be optimized. This is only supported by Mozilla-based browsers; use the standardized canvas.getContext('2d', { alpha: false }) instead.

width

The width of the coordinate space in CSS pixels. Defaults to 300.

Usage notes

Alternative content

You should provide alternate content inside the <canvas> block. That content will be rendered both on older browsers that don't support canvas and in browsers with JavaScript disabled.

Closing </canvas> tag

Unlike the <img> element, the <canvas> element requires the closing tag (</canvas>).

Sizing the canvas using CSS versus HTML

The displayed size of the canvas can be changed using CSS, but if you do this the image is scaled during rendering to fit the styled size, which can make the final graphics rendering end up being distorted.

It is better to specify your canvas dimensions by setting the width and height attributes directly on the <canvas> elements, either directly in the HTML or by using JavaScript.

Maximum canvas size

The exact maximum size of a <canvas> element depends on the browser and environment. While in most cases the maximum dimensions exceed 10,000 x 10,000 pixels, notably iOS devices limit the canvas size to only 4,096 x 4,096 pixels. See canvas size limits in different browsers and devices.

Using an offscreen canvas

A canvas can be rendered using the OffscreenCanvas API where the document and canvas are decoupled. The benefit is that a worker thread can handle canvas rendering and the main thread of your web application is not blocked by canvas operations. By parallelizing work, other UI elements of your web application will remain responsive even if you are running complex graphics on an offscreen canvas. For more information, see the OffscreenCanvas API documentation.

Accessibility

Alternative content

The <canvas> element on its own is just a bitmap and does not provide information about any drawn objects. Canvas content is not exposed to accessibility tools as semantic HTML is. In general, you should avoid using canvas in an accessible website or app. The following guides can help to make it more accessible.

• Canvas accessibility use cases
• Canvas element accessibility issues
• Best practices for interactive canvas elements

Examples

HTML

This code snippet adds a canvas element to your HTML document. A fallback text is provided if a browser is unable to read or render the canvas.

<canvas width="120" height="120">
  An alternative text describing what your canvas displays.
</canvas>

JavaScript

Then in the JavaScript code, call HTMLCanvasElement.getContext() to get a drawing context and start drawing onto the canvas:

const canvas = document.querySelector("canvas");
const ctx = canvas.getContext("2d");
ctx.fillStyle = "green";
// Add a rectangle at (10, 10) with size 100x100 pixels
ctx.fillRect(10, 10, 100, 100);

Result

Technical summary

Specifications

Browser compatibility

See also

• Canvas API
• Canvas tutorial
• OffscreenCanvas
• Canvas cheat sheet (2009)
• Canvas cheat sheet (pdf) (2015)
• Safari HTML canvas guide via Apple (2013)
• CanvasRenderingContext2D 2D drawing context for a canvas element via Apple.com
• WebGL API
• <img>
• SVG
• HTML video and audio