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 cairo- Extract GTK to C:\GTK
- Extract FreeType to C:\freetype
- Extract libjpeg-turn to C:\libjpeg-turbo
- Install CMake 3.3.2
- npm install -g node-gyp
> cd C:\freetype
> cmake . -G "Visual Studio 7"
> open VS solution
> change build to "release"
> build
> rename C:\freetype-2.6\release to C:\freetype-2.6\lib
> rename C:\freetype-2.6\include\freetype2 to C:\freetype-2.6\include\freetype
> rename C:\GTK\include\freetype2 to C:\GTK\include\freetype
When using this, kerning and font support was horrible. Regardless of PANGO or FreeType. The best freetype provided was that we could get decent font measurements but once fonts had smaller sizes than say 15pt/px the antialias in windows was utter garbage. This issue could be tracked down to here http://lists.cairographics.org/archives/cairo/2006-January/005954.html where...
But there's a general problem that text rendering antialiasing only works fully correctly in Windows if you draw directly to a no-alpha target surface with a mode of OVER and a solid color. Anything else, Pango needs to extract a mask from the windows text and draw with that, and then the Gamma correction that Windows text gets in the way rather than helping.
So to avoid this, we look to opentype.js which has a fantastic rendering of opentype fonts (TTF/OTF). With this in hand we can override the local canvas object with a custom fillText that uses open-type to do the actual render.
The only drawback to this approach is that when using fabric.js or some other script that extends canvas to support more interactive text layout we lose centering and right aligned text.
// override filltext so we get best rendering of fonts via opentype
canvas.fillText = canvas.contextContainer.fillText = function(text, top, left) {
var f = FontParser.parseFont(canvas.contextContainer.font);
var path = global._fonts[f.family].getPath(text, top, left, f.size);
path.fill = canvas.contextContainer.fillStyle;
path.draw(canvas.contextContainer);
};
For fabric, this means we had to hack in a fix for this...
// hack to work around text align not working
// on windows due to use of opentype as text rendering
// not canvas.fillText(...)
if (ctx.textAlign == 'center') {
var w = ctx.measureText(chars);
left = (left - (w.width/2));
} else if (ctx.textAlign == 'right') {
var w = ctx.measureText(chars);
left = (left - w.width);
}
var 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 <[email protected]>
Copyright (c) 2014 Automattic, Inc and contributors <[email protected]>
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.