index.js

var mapnik = require('mapnik'),
    sm = new (require('@mapbox/sphericalmercator'))(),
    mapnikify = require('@mapbox/geojson-mapnikify');

if (mapnik.register_default_input_plugins) {
    mapnik.register_default_input_plugins();
}

module.exports = Source;

require('util').inherits(Source, require('events').EventEmitter);

/**
 * Create a new source that returns tiles from a simplestyle-supporting
 * GeoJSON object.
 *
 * @param {string} uri
 * @param {function} callback
 * @returns {undefined}
 */
function Source(id, callback) {
    if (!id.startsWith('overlaydata://')) {
        return callback('Only the overlaydata protocol is supported');
    }

    var data = id.replace('overlaydata://', '');
    var retina = false;
    var legacy = false;

    if (data.indexOf('2x:') === 0) {
        retina = true;
        data = data.replace(/^2x:/, '');
    }

    if (data.indexOf('legacy:') === 0) {
        legacy = true;
        data = data.replace(/^legacy:/, '');
    }

    var parsed;
    try {
        parsed = JSON.parse(data);
    } catch (e) {
        return callback('invalid geojson');
    }

    mapnikify(parsed, retina, function(err, xml) {
        if (err) return callback(err);
        this._xml = xml;
        this._size = retina && !legacy ? 512 : 256;
        this._bufferSize = retina ? 128 : 64;
        callback(null, this);
    }.bind(this));
}

/**
 * Gets a tile from this source.
 *
 * @param {number} z
 * @param {number} x
 * @param {number} y
 * @param {function} callback
 */
Source.prototype.getTile = function(z, x, y, callback) {
    var size = this._size;
    var map = new mapnik.Map(size, size);
    map.bufferSize = this._bufferSize;

    try {
        map.fromString(this._xml, {}, function(err) {
            if (err) return callback(err);
            map.extent = sm.bbox(x, y, z, false, '900913');
            map.render(new mapnik.Image(size, size), {}, onrender);
        });
    } catch (e) {
        callback(e);
    }

    function onrender(err, im) {
        if (err) return callback(err);
        im.encode('png8:m=h:z=1', function(err, res) {
            callback(err, res);
        });
    }
};

/**
 * Gets a grid from this source: this will always fail, because
 * this source does not provide grids.
 *
 * @param {number} z
 * @param {number} x
 * @param {number} y
 * @param {function} callback
 */
Source.prototype.getGrid = function(z, x, y, callback) {
    callback('This source does not provide grids');
};

/**
 * Gets info from this source: this will always fail, because
 * this source does not provide info.
 *
 * @param {function} callback
 */
Source.prototype.getInfo = function(callback) {
    callback('This source does not provide info');
};

/**
 * @param {object} tilelive
 */
Source.registerProtocols = function(tilelive) {
    tilelive.protocols['overlaydata:'] = Source;
};