PureImage

PureImage is a pure JavaScript implementation of an image drawing and encoding API, based on HTML Canvas, for NodeJS. It has no native dependencies.

Current features:

• set pixels
• stroke and fill paths (rectangles, lines, quadratic curves)
• copy images
• export to PNG
• render text (no bold or italics yet)

Why?

The are more than enough drawing APIs out there. Why do we need another? My personal hatred of C/C++ compilers is widely known. The popular Node modules Canvas.js does a great job, but it's backed by Cairo, a C/C++ layer. I hate having native dependencies in Node modules. They often don't compile, or break after a system update. They often don't support non-X86 architectures (like the Raspberry Pi). You have to have a compiler already installed to use them, along with any other native dependencies preinstalled (like Cairo).

So, I made PureImage. It's goal is to implement the HTML Canvas spec in a headless Node buffer. No browser or window required.

PureImage is meant to be a small and maintainable Canvas library. It is not meant to be fast. If there are two choices of algorithm we will take the one with the simplest implementation, and preferably the fewest lines. We avoid special cases and optimizations to keep the code simple and maintainable. It should run everywhere and be highly portable. But it will not be fast. If you need speed go use Canvas.js.

PureImage uses only pure JS dependencies. OpenType for font parsing and PngJS for PNG export.

Examples

Make a new empty image, 100px by 50px. Automatically filled with 100% opaque black.

var PImage = require('pureimage');
var img1 = PImage.make(100,50);

Fill with a red rectangle, 50% opacity

var ctx = img1.getContext('2d');
ctx.setFillStyleRGBA(255,0,0, 0.5);
ctx.fillRect(0,0,100,100);

Write out to a PNG file (uses pngjs)

PImage.encodePNG(img1, fs.createWriteStream('out.png'), function(err) {
    console.log("wrote out the png file to out.png");
});

On the roadmap

• done drawing text from truetype files. Have to figure out a pure JS font rasterizer
• done: quadratic curves
• bezier curves, stroked and filled
• anti-aliased curves (partially done)
• full alpha compositing
• PNG loading for compositing
• Jpeg input/output

Thanks!

Thanks to Nodebox / EMRG for opentype.js

Thanks to Rosetta Code for Bresenham's in JS

Thanks to Kuba Niegowski for PngJS

Thanks to Eugene Ware for jpeg-js

Notes

• move font stuff to pure image,
• make a registerFont,
• setFont(name,size,weight,style,variant),
• and drawString function,
• and measureText