node-canvas is a Cairo backed Canvas implementation for NodeJS.
- TJ Holowaychuk (tj)
- Nathan Rajlich (TooTallNate)
- Rod Vagg (rvagg)
- Juriy Zaytsev (kangax)
$ npm install canvasUnless previously installed you'll need Cairo. For system-specific installation view the Wiki.
You can quickly install Cairo and its dependencies for OS X using the one liner below:
$ wget https://raw.githubusercontent.com/LearnBoost/node-canvas/master/install -O - | shor if you use MacPorts
sudo port install pkgconfig libpng giflib freetype libpixman cairovar Canvas = require('canvas')
, Image = Canvas.Image
, 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() + '" />');node-canvas extends the canvas API to provide interfacing with node, for example streaming PNG data, converting to a Buffer instance, etc. Among the interfacing API, in some cases the drawing API has been extended for SSJS image manipulation / creation usage, however keep in mind these additions may fail to render properly within browsers.
node-canvas adds Image#src=Buffer support, allowing you to read images from disc, redis, etc and apply them via ctx.drawImage(). Below we draw scaled down squid png by reading it from the disk with node's I/O.
fs.readFile(__dirname + '/images/squid.png', function(err, squid){
if (err) throw err;
img = new Image;
img.src = squid;
ctx.drawImage(img, 0, 0, img.width / 4, img.height / 4);
});Below is an example of a canvas drawing it-self as the source several time:
var img = new Image;
img.src = canvas.toBuffer();
ctx.drawImage(img, 0, 0, 50, 50);
ctx.drawImage(img, 50, 0, 50, 50);
ctx.drawImage(img, 100, 0, 50, 50);node-canvas adds Image#dataMode support, which can be used to opt-in to mime data tracking of images (currently only JPEGs).
When mime data is tracked, in PDF mode JPEGs can be embedded directly into the output, rather than being re-encoded into PNG. This can drastically reduce filesize, and speed up rendering.
var img = new Image;
img.dataMode = Image.MODE_IMAGE; // Only image data tracked
img.dataMode = Image.MODE_MIME; // Only mime data tracked
img.dataMode = Image.MODE_MIME | Image.MODE_IMAGE; // Both are trackedIf image data is not tracked, and the Image is drawn to an image rather than a PDF canvas, the output will be junk. Enabling mime data tracking has no benefits (only a slow down) unless you are generating a PDF.
To create a PNGStream simply call canvas.pngStream(), 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.pngStream();
stream.on('data', function(chunk){
out.write(chunk);
});
stream.on('end', function(){
console.log('saved png');
});Currently only sync streaming is supported, however we plan on supporting async streaming as well (of course :) ). Until then the Canvas#toBuffer(callback) alternative is async utilizing eio_custom().
You can likewise create a JPEGStream by calling canvas.jpegStream() with
some optional parameters; functionality is otherwise identical to
pngStream(). See examples/crop.js for an example.
Note: At the moment, jpegStream() is the same as syncJPEGStream(), both
are synchronous
var stream = canvas.jpegStream({
bufsize: 4096 // output buffer size in bytes, default: 4096
, quality: 75 // JPEG quality (0-100) default: 75
, progressive: false // true for progressive compression, default: false
});A call to Canvas#toBuffer() will return a node Buffer instance containing all of the PNG data.
canvas.toBuffer();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){
});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){
});Given one of the values below will alter pattern (gradients, images, etc) render quality, defaults to good.
- fast
- good
- best
- nearest
- bilinear
Can be either path or glyph. Using glyph is much faster than path for drawing, and when using a PDF context will embed the text natively, so will be selectable and lower filesize. The downside is that cairo does not have any subpixel precision for glyph, so this will be noticeably lower quality for text positioning in cases such as rotated text. Also, strokeText in glyph will act the same as fillText, except using the stroke style for the fill.
Defaults to path.
This property is tracked as part of the canvas state in save/restore.
Like patternQuality, but applies to transformations effecting more than just patterns. Defaults to good.
- fast
- good
- best
- nearest
- bilinear
In addition to those specified and commonly implemented by browsers, the following have been added:
- multiply
- screen
- overlay
- hard-light
- soft-light
- hsl-hue
- hsl-saturation
- hsl-color
- hsl-luminosity
Set anti-aliasing mode
- default
- none
- gray
- subpixel
For example:
ctx.antialias = 'none';Basic PDF support was added in 0.11.0. Make sure to install cairo with --enable-pdf=yes for the PDF backend. node-canvas must know that it is creating
a PDF on initialization, using the "pdf" string:
var canvas = new Canvas(200, 500, 'pdf');An additional method .addPage() is then available to create
multiple page PDFs:
ctx.font = '22px Helvetica';
ctx.fillText('Hello World', 50, 80);
ctx.addPage();
ctx.font = '22px Helvetica';
ctx.fillText('Hello World 2', 50, 80);
ctx.addPage();
ctx.font = '22px Helvetica';
ctx.fillText('Hello World 3', 50, 80);
ctx.addPage();Just like PDF support, make sure to install cairo with --enable-svg=yes.
You also need to tell node-canvas that it is working on SVG upon its initialization:
var canvas = new Canvas(200, 500, 'svg');
// Use the normal primitives.
fs.writeFile('out.svg', canvas.toBuffer());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.
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 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.
If you have not previously, init git submodules:
$ git submodule update --init
Install the node modules:
$ npm install
Build node-canvas:
$ node-gyp rebuild
Unit tests:
$ make test
Visual tests:
$ make test-server
Tested with and designed for:
- node 0.4.2
- cairo 1.8.6
For node 0.2.x node-canvas <= 0.4.3 may be used,
0.5.0 and above are designed for node 0.4.x only.
(The MIT License)
Copyright (c) 2010 LearnBoost, and contributors <dev@learnboost.com>
Copyright (c) 2014 Automattic, Inc and contributors <dev@automattic.com>
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