node

node-mapbox-gl-native

Installing

Requires a modern C++ runtime that supports C++14.

By default, installs binaries. On these platforms no additional dependencies are needed.

• 64 bit macOS or 64 bit Linux
• Node.js v4.x (note: v5+ is known to have issues)

Run:

npm install mapbox-gl-native

Other platforms will fall back to a source compile with make node; see INSTALL.md in the repository root directory for prequisites.

Testing

npm test
npm run test-suite

Rendering a map tile

var fs = require('fs');
var path = require('path');
var mbgl = require('mapbox-gl-native');
var sharp = require('sharp');

var options = {
  request: function(req, callback) {
    fs.readFile(path.join(__dirname, 'test', req.url), function(err, data) {
      callback(err, { data: data });
    });
  },
  ratio: 1
};

var map = new mbgl.Map(options);

map.load(require('./test/fixtures/style.json'));

map.render({zoom: 0}, function(err, buffer) {
    if (err) throw err;

    map.release();

    var image = sharp(buffer, {
        raw: {
            width: 512,
            height: 512,
            channels: 4
        }
    });

    // Convert raw image buffer to PNG
    image.toFile('image.png', function(err) {
        if (err) throw err;
    });
});

The first argument passed to map.render is an options object, all keys are optional:

{
    zoom: {zoom}, // number, defaults to 0
    width: {width}, // number (px), defaults to 512
    height: {height}, // number (px), defaults to 512
    center: [{longitude}, {latitude}], // array of numbers (coordinates), defaults to [0,0]
    bearing: {bearing}, // number (in degrees, counter-clockwise from north), defaults to 0
    pitch: {pitch}, // number (in degrees, arcing towards the horizon), defaults to 0
    classes: {classes} // array of strings
}

When you are finished using a map object, you can call map.release() to permanently dispose the internal map resources. This is not necessary, but can be helpful to optimize resource usage (memory, file sockets) on a more granualar level than V8's garbage collector. Calling map.release() will prevent a map object from being used for any further render calls, but can be safely called as soon as the map.render() callback returns, as the returned pixel buffer will always be retained for the scope of the callback.

Implementing a file source

When creating a Map, you must pass an options object (with a required request method and optional 'ratio' number) as the first parameter.

var map = new mbgl.Map({
    request: function(req) {
        // TODO
    },
    ratio: 2.0
});

The request() method handles a request for a resource. The ratio sets the scale at which the map will render tiles, such as 2.0 for rendering images for high pixel density displays. The req parameter has two properties:

{
    "url": "http://example.com",
    "kind": 1
}

The kind is an enum and defined in mbgl.Resource:

{
    "Unknown": 0,
    "Style": 1,
    "Source": 2,
    "Tile": 3,
    "Glyphs": 4,
    "SpriteImage": 5,
    "SpriteJSON": 6
}

The kind enum has no significance for anything but serves as a hint to your implemention as to what sort of resource to expect. E.g., your implementation could choose caching strategies based on the expected file type.

The request implementation should pass uncompressed data to callback. If you are downloading assets from a source that applies gzip transport encoding, the implementation must decompress the results before passing them on.

A sample implementation that reads files from disk would look like the following:

var map = new mbgl.Map({
    request: function(req, callback) {
        fs.readFile(path.join('base/path', req.url), function(err, data) {
            callback(err, { data: data });
        });
    }
});

This is a very barebones implementation and you'll probably want a better implementation. E.g. it passes the url verbatim to the file system, but you'd want add some logic that normalizes http URLs. You'll notice that once your implementation has obtained the requested file, you have to deliver it to the requestee by calling callback(), which takes either an error object or null and an object with several keys:

{
    modified: new Date(),
    expires: new Date(),
    etag: "string",
    data: new Buffer()
}

A sample implementation that uses request to fetch data from a remote source:

var mbgl = require('mapbox-gl-native');
var request = require('request');

var map = new mbgl.Map({
    request: function(req, callback) {
        request({
            url: req.url,
            encoding: null,
            gzip: true
        }, function (err, res, body) {
            if (err) {
                callback(err);
            } else if (res.statusCode == 200) {
                var response = {};

                if (res.headers.modified) { response.modified = new Date(res.headers.modified); }
                if (res.headers.expires) { response.expires = new Date(res.headers.expires); }
                if (res.headers.etag) { response.etag = res.headers.etag; }
                
                response.data = body;
                
                callback(null, response);
            } else {
                callback(new Error(JSON.parse(body).message));
            }
        });
    }
});

Stylesheets are free to use any protocols, but your implementation of request must support these; e.g. you could use s3:// to indicate that files are supposed to be loaded from S3.

Listening for log events

The module imported with require('mapbox-gl-native') inherits from EventEmitter, and the NodeLogObserver will push log events to this. Log messages can have class, severity, code (HTTP status codes), and text parameters.

var mbgl = require('mapbox-gl-native');
mbgl.on('message', function(msg) {
    t.ok(msg, 'emits error');
    t.equal(msg.class, 'Style');
    t.equal(msg.severity, 'ERROR');
    t.ok(msg.text.match(/Failed to load/), 'error text matches');
});

Contributing

See DEVELOPING.md for instructions on building this module for development.