README.md

@maplibre/maplibre-gl-native

Installing

Binaries are available and downloaded during install for the following platforms:

• Operating systems:
  • Ubuntu 22.04 (amd64/arm64)
  • macOS 12 (amd64/arm64)
  • Windows (amd64)
• Node.js 16, 18, 20

Run:

npm install @maplibre/maplibre-gl-native

Further platforms might work with additional libraries installed.

Testing

npm test

Rendering a map tile

The minimal example requires only the instantiation of the mbgl.Map object, loading a style and calling the map.render method:

var mbgl = require('@maplibre/maplibre-gl-native');
var sharp = require('sharp');

var map = new mbgl.Map();

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

map.render(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;
    });
});

But you can customize the map providing an options object to mbgl.Map constructor and to map.render method:

var fs = require('fs');
var path = require('path');
var mbgl = require('@maplibre/maplibre-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 granular 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 can optionally pass an options object (with an optional request method and optional ratio number) as the first parameter. 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:

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

If you omit the request method, the map object will use the default internal request handlers, which is ok for most cases. However, if you have specific needs, you can implement your own request handler. When a request method is provided, all map resources will be requested by calling the request method with two parameters, called req and callback respectively in this example. 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 callback parameter is a function that must be called with two parameters: an error message (if there are no errors, then you must pass null), and a response object:

{
    data: {data}, // required, must be a byte array, usually a Buffer object
    modified: {modified}, // Date, optional
    expires: {expires}, // Date, optional
    etag: {etag} // string, optional
}

If there is no data to be sent to the callback (empty data, or no-content respose), then it must be called without parameters. 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('@maplibre/maplibre-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 if (res.statusCode == 204) {
                callback();
            } 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('maplibre-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('@maplibre/maplibre-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.