Canvas API

Added in HTML5, the HTML <canvas> element can be used to draw graphics via scripting in JavaScript. For example, it can be used to draw graphs, make photo compositions, create animations, or even do real-time video processing or rendering.

Mozilla applications gained support for <canvas> starting with Gecko 1.8 (i.e. Firefox 1.5). The element was originally introduced by Apple for the OS X Dashboard and Safari. Internet Explorer supports <canvas> from version 9 onwards; for earlier versions of IE, a page can effectively add support for <canvas> by including a script from Google's Explorer Canvas project. Google Chrome and Opera 9 also support <canvas>.

The <canvas> element is also used by WebGL to do hardware-accelerated 3D graphics on web pages.

Example

This is just a simple code snippet which uses the CanvasRenderingContext2D.fillRect() method.

HTML

<canvas id="canvas"></canvas>

JavaScript

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

ctx.fillStyle = "green";
ctx.fillRect(10, 10, 100, 100);

Edit the code below and see your changes update live in the canvas:

<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
ctx.fillStyle = "green";
ctx.fillRect(10, 10, 100, 100);</textarea>

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);

Reference

The interfaces related to the WebGLRenderingContext are referenced under WebGL.

Guides and tutorials

Canvas tutorial

A comprehensive tutorial covering both the basic usage of <canvas> and its advanced features.

Code snippets: Canvas

Some extension developer-oriented code snippets involving <canvas>.

Demo: A basic ray-caster

A demo of ray-tracing animation using canvas.

Drawing DOM objects into a canvas

How to draw DOM content, such as HTML elements, into a canvas.

Manipulating video using canvas

Combining <video> and <canvas> to manipulate video data in real time.

Resources

Generic

• HTML5 Canvas Deep Dive
• Canvas Handbook

Libraries

• Fabric.js is an open-source canvas library with SVG parsing capabilities.
• Kinetic.js is an open-source canvas library focused on interactivity for desktop and mobile applications.
• Paper.js is an open source vector graphics scripting framework that runs on top of the HTML5 Canvas.
• libCanvas is powerful and lightweight canvas framework.
• Processing.js is a port of the Processing visualization language.
• PlayCanvas is an open source game engine.
• Pixi.js is an open source game engine.
• PlotKit is a charting and graphing library.
• Rekapi is an animation key-framing API for Canvas.
• PhiloGL is a WebGL framework for data visualization, creative coding and game development.
• JavaScript InfoVis Toolkit creates interactive 2D Canvas data visualizations for the Web.

Specifications

See also

• WebGL