node-canvas

Node canvas is a Cairo backed Canvas implementation for NodeJS.

Authors

• TJ Holowaychuk (visionmedia)

Installation

$ npm install canvas

If not previously installed, you will want to install the cairo graphics library version >= 1.8.6 first using the package manager available to you, or building from source.

Screencasts

• Introduction

Example

var Canvas = require('canvas')
  , canvas = new Canvas(200,200)
  , ctx = canvas.getContext('2d');


  ctx.font = '30px Impact';
  ctx.rotate(.1);
  ctx.fillText("Awesome!", 50, 100);

  var te = ctx.measureText('Awesome!');
  ctx.strokeStyle = 'rgba(0,0,0,0.5)';
  ctx.beginPath();
  ctx.lineTo(50, 102);
  ctx.lineTo(50 + te.width, 102);
  ctx.stroke();
  
  console.log('<img src="' + canvas.toDataURL() + '" />');

Non-Standard API

Due to interfacing with existing node internals such as I/O node-canvas includes a non-standard API which is shown below.

Canvas#createPNGStream()

To create a PNGStream simple call canvas.createPNGStream(), and the stream will start to emit data events, finally emitting end when finished. If an exception occurs the error event is emitted.

var fs = require('fs')
  , out = fs.createWriteStream(__dirname + '/text.png')
  , stream = canvas.createPNGStream();

stream.on('data', function(chunk){
  out.write(chunk);
});

stream.on('end', function(){
  console.log('saved png');
});

Canvas#toBuffer()

A call to Canvas#toBuffer() will return a node Buffer instance containing all of the PNG data.

canvas.toBuffer();

Canvas#toBuffer() async

Optionally we may pass a callback function to Canvas#toBuffer(), and this process will be performed asynchronously, and will callback(err, buf).

canvas.toBuffer(function(err, buf){

});

Canvas#toDataURL() async

Optionally we may pass a callback function to Canvas#toDataURL(), and this process will be performed asynchronously, and will callback(err, str).

canvas.toDataURL(function(err, str){
  
});

or specify the mime type:

canvas.toDataURL('image/png', function(err, str){
  
});

Benchmarks

Although node-canvas is extremely new, and we have not even begun optimization yet it is already quite fast. For benchmarks vs other node canvas implementations view this gist, or update the submodules and run $ make benchmark yourself.

Contribute

Want to contribute to node-canvas? patches for features, bug fixes, documentation, examples and others are certainly welcome. Take a look at the issue queue for existing issues.

Examples

Examples are placed in ./examples, be sure to check them out! most produce a png image of the same name, and others such as live-clock.js launch an http server to be viewed in the browser.

Testing

If you have not previously, init git submodules:

$ git submodule update --init

Build node-canvas:

$ node-waf configure build

Unit tests:

$ make test

Visual tests:

$ make test-server

Versions

Tested with:

• node 0.2.4
• cairo 1.8.6

License

(The MIT License)

Copyright (c) 2010 LearnBoost <dev@learnboost.ca>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.