Use the <canvas>
with either the canvas scripting API or the WebGL API to draw graphics and animations.
Content categories | Flow content, phrasing content, embedded content, palpable content. |
---|---|
Permitted content | Transparent but with no interactive content descendants except for <a> elements, <button> elements, <input> elements whose type attribute is checkbox , radio , or button . |
Tag omission | None, both the starting and ending tag are mandatory. |
Permitted parents | Any element that accepts phrasing content. |
Implicit ARIA role | No corresponding role |
Permitted ARIA roles | Any |
DOM interface | HTMLCanvasElement |
This element's attributes include the global attributes.
height
moz-opaque
canvas.getContext('2d', { alpha: false })
instead.width
You may (and 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. Providing a useful fallback text or sub DOM helps to make the the canvas more accessible.
Unlike the <img>
element, the <canvas>
element requires the closing tag (</canvas>
).
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.
The maximum size of a <canvas>
element is very large, but the exact size depends on the browser. The following is some data we've collected from various tests and other sources (e.g. Stack Overflow):
Browser | Maximum height | Maximum width | Maximum area |
---|---|---|---|
Chrome | 32,767 pixels | 32,767 pixels | 268,435,456 pixels (i.e., 16,384 x 16,384) |
Firefox | 32,767 pixels | 32,767 pixels | 472,907,776 pixels (i.e., 22,528 x 20,992) |
Safari | 32,767 pixels | 32,767 pixels | 268,435,456 pixels (i.e., 16,384 x 16,384) |
IE | 8,192 pixels | 8,192 pixels | ? |
Note: Exceeding the maximum dimensions or area renders the canvas unusable — drawing commands will not work.
This code snippet adds a canvas element to your HTML document. A fallback text is provided if a browser is unable to render the canvas, or if can't read a canvas.
<canvas width="300" height="300"> An alternative text describing what your canvas displays. </canvas>
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'; ctx.fillRect(10, 10, 100, 100);
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.
Specification | Status | Comment |
---|---|---|
HTML Living Standard The definition of '<canvas>' in that specification. | Living Standard | |
HTML5 The definition of '<canvas>' in that specification. | Recommendation | Initial definition |
Desktop | ||||||
---|---|---|---|---|---|---|
canvas |
1 | 12 | 1.5
|
9 | 9 | 2
|
height |
1 | 12 | 1.5
|
9 | 9 | 2
|
moz-opaque
|
No | No | 3.5 | No | No | No |
width |
1 | 12 | 1.5
|
9 | 9 | 2
|
Mobile | ||||||
---|---|---|---|---|---|---|
canvas |
37 | 18 | 4
|
10.1 | 1 | 1.0 |
height |
37 | 18 | 4
|
10.1 | 1 | 1.0 |
moz-opaque
|
No | No | 4 | No | No | No |
width |
37 | 18 | 4
|
10.1 | 1 | 1.0 |
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/canvas