tile-retriever/dist/tile-retriever.js

Load vector tiles from sources described in MapLibre style documents

import Protobuf from 'pbf-esm';

function classifyRings(rings) {
  // Classifies an array of rings into polygons with outer rings and holes
  if (rings.length <= 1) return [rings];

  const polygons = [];
  let polygon, ccw;

  rings.forEach(ring => {
    const area = signedArea(ring);
    if (area === 0) return;

    if (ccw === undefined) ccw = area < 0;

    if (ccw === area < 0) {
      if (polygon) polygons.push(polygon);
      polygon = [ring];

    } else {
      polygon.push(ring);
    }
  });
  if (polygon) polygons.push(polygon);

  return polygons;
}

function signedArea(ring) {
  const xmul = (p1, p2) => (p2.x - p1.x) * (p1.y + p2.y);

  const initialValue = xmul(ring[0], ring[ring.length - 1]);

  return ring.slice(1)  // NOTE: skips ring[0], shifts index
    .reduce( (sum, p1, i) => sum + xmul(p1, ring[i]), initialValue );
}

const types = ["Unknown", "Point", "LineString", "Polygon"];

function toGeoJSON(size, sx = 0, sy = 0) {
  // Input size is the side length of the (square) area over which the
  //  coordinate space of this tile [0, this.extent] will be rendered.
  // Input sx, sy is the origin (top left corner) of the output coordinates
  //  within the (size x size) rendered area of the full tile.

  size = size || this.extent;
  const scale = size / this.extent;
  let coords = this.loadGeometry();
  let type = types[this.type];

  function project(line) {
    return line.map(p => [p.x * scale - sx, p.y * scale - sy]);
  }

  switch (type) {
    case "Point":
      coords = project( coords.map(p => p[0]) );
      break;

    case "LineString":
      coords = coords.map(project);
      break;

    case "Polygon":
      coords = classifyRings(coords);
      coords = coords.map(polygon => polygon.map(project));
      break;
  }

  if (coords.length === 1) {
    coords = coords[0];
  } else {
    type = "Multi" + type;
  }

  const result = {
    type: "Feature",
    geometry: {
      type: type,
      coordinates: coords
    },
    properties: this.properties
  };

  if ("id" in this) result.id = this.id;

  return result;
}

function VectorTileFeature(pbf, end, extent, keys, values) {
  // Public
  this.properties = {};
  this.extent = extent;
  this.type = 0;

  // Private
  this._pbf = pbf;
  this._geometry = -1;
  this._keys = keys;
  this._values = values;

  pbf.readFields(readFeature, this, end);
}

function readFeature(tag, feature, pbf) {
  if (tag == 1) feature.id = pbf.readVarint();
  else if (tag == 2) readTag(pbf, feature);
  else if (tag == 3) feature.type = pbf.readVarint();
  else if (tag == 4) feature._geometry = pbf.pos;
}

function readTag(pbf, feature) {
  const end = pbf.readVarint() + pbf.pos;
  const { _keys, _values } = feature;

  while (pbf.pos < end) {
    const key = _keys[pbf.readVarint()];
    const value = _values[pbf.readVarint()];
    feature.properties[key] = value;
  }
}

VectorTileFeature.prototype.loadGeometry = function() {
  const pbf = this._pbf;
  pbf.pos = this._geometry;

  const end = pbf.readVarint() + pbf.pos;
  let cmd = 1;
  let length = 0;
  let x = 0;
  let y = 0;
  const lines = [];
  let line;

  while (pbf.pos < end) {
    if (length <= 0) {
      const cmdLen = pbf.readVarint();
      cmd = cmdLen & 0x7;
      length = cmdLen >> 3;
    }

    length--;

    if (cmd === 1 || cmd === 2) {
      x += pbf.readSVarint();
      y += pbf.readSVarint();

      if (cmd === 1) { // moveTo
        if (line) lines.push(line);
        line = [];
      }

      line.push({ x, y });

    } else if (cmd === 7) {
      // Workaround for https://github.com/mapbox/mapnik-vector-tile/issues/90
      if (line) line.push({ // closePolygon
        x: line[0].x,
        y: line[0].y
      });

    } else {
      throw Error("unknown command " + cmd);
    }
  }

  if (line) lines.push(line);

  return lines;
};

VectorTileFeature.prototype.bbox = function() {
  const pbf = this._pbf;
  pbf.pos = this._geometry;

  const end = pbf.readVarint() + pbf.pos;
  let cmd = 1;
  let length = 0;
  let x = 0;
  let y = 0;
  let x1 = Infinity;
  let x2 = -Infinity;
  let y1 = Infinity;
  let y2 = -Infinity;

  while (pbf.pos < end) {
    if (length <= 0) {
      const cmdLen = pbf.readVarint();
      cmd = cmdLen & 0x7;
      length = cmdLen >> 3;
    }

    length--;

    if (cmd === 1 || cmd === 2) {
      x += pbf.readSVarint();
      y += pbf.readSVarint();
      if (x < x1) x1 = x;
      if (x > x2) x2 = x;
      if (y < y1) y1 = y;
      if (y > y2) y2 = y;

    } else if (cmd !== 7) {
      throw Error("unknown command " + cmd);
    }
  }

  return [x1, y1, x2, y2];
};

VectorTileFeature.types = types;
VectorTileFeature.prototype.toGeoJSON = toGeoJSON;

function VectorTileLayer(pbf, end) {
  // Public
  this.version = 1;
  this.name = null;
  this.extent = 4096;
  this.length = 0;

  // Private
  this._pbf = pbf;
  this._keys = [];
  this._values = [];
  this._features = [];

  pbf.readFields(readLayer, this, end);

  this.length = this._features.length;
}

function readLayer(tag, layer, pbf) {
  if (tag === 15) layer.version = pbf.readVarint();
  else if (tag === 1) layer.name = pbf.readString();
  else if (tag === 5) layer.extent = pbf.readVarint();
  else if (tag === 2) layer._features.push(pbf.pos);
  else if (tag === 3) layer._keys.push(pbf.readString());
  else if (tag === 4) layer._values.push(readValueMessage(pbf));
}

function readValueMessage(pbf) {
  let value = null;
  const end = pbf.readVarint() + pbf.pos;

  while (pbf.pos < end) {
    const tag = pbf.readVarint() >> 3;

    value = tag === 1 ? pbf.readString() :
      tag === 2 ? pbf.readFloat() :
      tag === 3 ? pbf.readDouble() :
      tag === 4 ? pbf.readVarint64() :
      tag === 5 ? pbf.readVarint() :
      tag === 6 ? pbf.readSVarint() :
      tag === 7 ? pbf.readBoolean() : null;
  }

  return value;
}

// return feature 'i' from this layer as a 'VectorTileFeature'
VectorTileLayer.prototype.feature = function(i) {
  const { _features, extent, _pbf, _keys, _values } = this;

  const lastFeature = _features.length - 1;
  if (i < 0 || i > lastFeature) throw Error("feature index out of bounds");

  _pbf.pos = _features[i];

  const end = _pbf.readVarint() + _pbf.pos;
  return new VectorTileFeature(_pbf, end, extent, _keys, _values);
};

VectorTileLayer.prototype.toGeoJSON = function(size, sx, sy) {
  const features = Array.from(Array(this._features.length), (v, i) => {
    return this.feature(i).toGeoJSON(size, sx, sy);
  });

  return { type: "FeatureCollection", features, extent: this.extent };
};

function VectorTile(pbf, end) {
  this.layers = pbf.readFields(readTile, {}, end);
}

function readTile(tag, layers, pbf) {
  if (tag === 3) {
    const layer = new VectorTileLayer(pbf, pbf.readVarint() + pbf.pos);
    if (layer.length) layers[layer.name] = layer;
  }
}

function xhrGet(href, type, callback) {
  const req = new XMLHttpRequest();

  req.responseType = type;
  req.onerror = errHandler;
  req.onabort = errHandler;
  req.onload = loadHandler;

  req.open("get", href);
  req.send();

  function errHandler(e) {
    return callback(xhrErr("ended with an ", e.type));
  }

  function loadHandler() {
    const { responseType, status, response } = req;

    const err = (responseType !== type) ?
      xhrErr("Expected responseType ", type, ", got ", responseType) :
      (status !== 200) ? xhrErr("HTTP ", status, " error from ", href) :
      null;

    return callback(err, response);
  }

  return req; // Request can be aborted via req.abort()
}

function xhrErr(...strings) {
  return "XMLHttpRequest: " + strings.join("");
}

function initMVT(source) {
  const getURL = initUrlFunc(source.tiles);

  // TODO: use VectorTile.extent. Requires changes in dependencies, dependents
  const size = 512;

  return function(tileCoords, callback) {
    const { z, x, y } = tileCoords;
    const dataHref = getURL(z, x, y);

    return xhrGet(dataHref, "arraybuffer", parseMVT);

    function parseMVT(err, data) {
      if (err) return callback(err, data);
      const tile = new VectorTile(new Protobuf(data));
      const json = Object.values(tile.layers)
        .reduce((d, l) => (d[l.name] = l.toGeoJSON(size), d), {});
      callback(null, json);
    }
  };
}

function initUrlFunc(endpoints) {
  // Use a different endpoint for each request
  let index = 0;

  return function(z, x, y) {
    index = (index + 1) % endpoints.length;
    const endpoint = endpoints[index];
    return endpoint.replace(/{z}/, z).replace(/{x}/, x).replace(/{y}/, y);
  };
}

// calculate simplification data using optimized Douglas-Peucker algorithm

function simplify(coords, first, last, sqTolerance) {
    var maxSqDist = sqTolerance;
    var mid = (last - first) >> 1;
    var minPosToMid = last - first;
    var index;

    var ax = coords[first];
    var ay = coords[first + 1];
    var bx = coords[last];
    var by = coords[last + 1];

    for (var i = first + 3; i < last; i += 3) {
        var d = getSqSegDist(coords[i], coords[i + 1], ax, ay, bx, by);

        if (d > maxSqDist) {
            index = i;
            maxSqDist = d;

        } else if (d === maxSqDist) {
            // a workaround to ensure we choose a pivot close to the middle of the list,
            // reducing recursion depth, for certain degenerate inputs
            // https://github.com/mapbox/geojson-vt/issues/104
            var posToMid = Math.abs(i - mid);
            if (posToMid < minPosToMid) {
                index = i;
                minPosToMid = posToMid;
            }
        }
    }

    if (maxSqDist > sqTolerance) {
        if (index - first > 3) simplify(coords, first, index, sqTolerance);
        coords[index + 2] = maxSqDist;
        if (last - index > 3) simplify(coords, index, last, sqTolerance);
    }
}

// square distance from a point to a segment
function getSqSegDist(px, py, x, y, bx, by) {

    var dx = bx - x;
    var dy = by - y;

    if (dx !== 0 || dy !== 0) {

        var t = ((px - x) * dx + (py - y) * dy) / (dx * dx + dy * dy);

        if (t > 1) {
            x = bx;
            y = by;

        } else if (t > 0) {
            x += dx * t;
            y += dy * t;
        }
    }

    dx = px - x;
    dy = py - y;

    return dx * dx + dy * dy;
}

function createFeature(id, type, geom, tags) {
    var feature = {
        id: typeof id === 'undefined' ? null : id,
        type: type,
        geometry: geom,
        tags: tags,
        minX: Infinity,
        minY: Infinity,
        maxX: -Infinity,
        maxY: -Infinity
    };
    calcBBox(feature);
    return feature;
}

function calcBBox(feature) {
    var geom = feature.geometry;
    var type = feature.type;

    if (type === 'Point' || type === 'MultiPoint' || type === 'LineString') {
        calcLineBBox(feature, geom);

    } else if (type === 'Polygon' || type === 'MultiLineString') {
        for (var i = 0; i < geom.length; i++) {
            calcLineBBox(feature, geom[i]);
        }

    } else if (type === 'MultiPolygon') {
        for (i = 0; i < geom.length; i++) {
            for (var j = 0; j < geom[i].length; j++) {
                calcLineBBox(feature, geom[i][j]);
            }
        }
    }
}

function calcLineBBox(feature, geom) {
    for (var i = 0; i < geom.length; i += 3) {
        feature.minX = Math.min(feature.minX, geom[i]);
        feature.minY = Math.min(feature.minY, geom[i + 1]);
        feature.maxX = Math.max(feature.maxX, geom[i]);
        feature.maxY = Math.max(feature.maxY, geom[i + 1]);
    }
}

// converts GeoJSON feature into an intermediate projected JSON vector format with simplification data

function convert(data, options) {
    var features = [];
    if (data.type === 'FeatureCollection') {
        for (var i = 0; i < data.features.length; i++) {
            convertFeature(features, data.features[i], options, i);
        }

    } else if (data.type === 'Feature') {
        convertFeature(features, data, options);

    } else {
        // single geometry or a geometry collection
        convertFeature(features, {geometry: data}, options);
    }

    return features;
}

function convertFeature(features, geojson, options, index) {
    if (!geojson.geometry) return;

    var coords = geojson.geometry.coordinates;
    var type = geojson.geometry.type;
    var tolerance = Math.pow(options.tolerance / ((1 << options.maxZoom) * options.extent), 2);
    var geometry = [];
    var id = geojson.id;
    if (options.promoteId) {
        id = geojson.properties[options.promoteId];
    } else if (options.generateId) {
        id = index || 0;
    }
    if (type === 'Point') {
        convertPoint(coords, geometry);

    } else if (type === 'MultiPoint') {
        for (var i = 0; i < coords.length; i++) {
            convertPoint(coords[i], geometry);
        }

    } else if (type === 'LineString') {
        convertLine(coords, geometry, tolerance, false);

    } else if (type === 'MultiLineString') {
        if (options.lineMetrics) {
            // explode into linestrings to be able to track metrics
            for (i = 0; i < coords.length; i++) {
                geometry = [];
                convertLine(coords[i], geometry, tolerance, false);
                features.push(createFeature(id, 'LineString', geometry, geojson.properties));
            }
            return;
        } else {
            convertLines(coords, geometry, tolerance, false);
        }

    } else if (type === 'Polygon') {
        convertLines(coords, geometry, tolerance, true);

    } else if (type === 'MultiPolygon') {
        for (i = 0; i < coords.length; i++) {
            var polygon = [];
            convertLines(coords[i], polygon, tolerance, true);
            geometry.push(polygon);
        }
    } else if (type === 'GeometryCollection') {
        for (i = 0; i < geojson.geometry.geometries.length; i++) {
            convertFeature(features, {
                id: id,
                geometry: geojson.geometry.geometries[i],
                properties: geojson.properties
            }, options, index);
        }
        return;
    } else {
        throw new Error('Input data is not a valid GeoJSON object.');
    }

    features.push(createFeature(id, type, geometry, geojson.properties));
}

function convertPoint(coords, out) {
    out.push(projectX(coords[0]));
    out.push(projectY(coords[1]));
    out.push(0);
}

function convertLine(ring, out, tolerance, isPolygon) {
    var x0, y0;
    var size = 0;

    for (var j = 0; j < ring.length; j++) {
        var x = projectX(ring[j][0]);
        var y = projectY(ring[j][1]);

        out.push(x);
        out.push(y);
        out.push(0);

        if (j > 0) {
            if (isPolygon) {
                size += (x0 * y - x * y0) / 2; // area
            } else {
                size += Math.sqrt(Math.pow(x - x0, 2) + Math.pow(y - y0, 2)); // length
            }
        }
        x0 = x;
        y0 = y;
    }

    var last = out.length - 3;
    out[2] = 1;
    simplify(out, 0, last, tolerance);
    out[last + 2] = 1;

    out.size = Math.abs(size);
    out.start = 0;
    out.end = out.size;
}

function convertLines(rings, out, tolerance, isPolygon) {
    for (var i = 0; i < rings.length; i++) {
        var geom = [];
        convertLine(rings[i], geom, tolerance, isPolygon);
        out.push(geom);
    }
}

function projectX(x) {
    return x / 360 + 0.5;
}

function projectY(y) {
    var sin = Math.sin(y * Math.PI / 180);
    var y2 = 0.5 - 0.25 * Math.log((1 + sin) / (1 - sin)) / Math.PI;
    return y2 < 0 ? 0 : y2 > 1 ? 1 : y2;
}

/* clip features between two axis-parallel lines:
 *     |        |
 *  ___|___     |     /
 * /   |   \____|____/
 *     |        |
 */

function clip(features, scale, k1, k2, axis, minAll, maxAll, options) {

    k1 /= scale;
    k2 /= scale;

    if (minAll >= k1 && maxAll < k2) return features; // trivial accept
    else if (maxAll < k1 || minAll >= k2) return null; // trivial reject

    var clipped = [];

    for (var i = 0; i < features.length; i++) {

        var feature = features[i];
        var geometry = feature.geometry;
        var type = feature.type;

        var min = axis === 0 ? feature.minX : feature.minY;
        var max = axis === 0 ? feature.maxX : feature.maxY;

        if (min >= k1 && max < k2) { // trivial accept
            clipped.push(feature);
            continue;
        } else if (max < k1 || min >= k2) { // trivial reject
            continue;
        }

        var newGeometry = [];

        if (type === 'Point' || type === 'MultiPoint') {
            clipPoints(geometry, newGeometry, k1, k2, axis);

        } else if (type === 'LineString') {
            clipLine(geometry, newGeometry, k1, k2, axis, false, options.lineMetrics);

        } else if (type === 'MultiLineString') {
            clipLines(geometry, newGeometry, k1, k2, axis, false);

        } else if (type === 'Polygon') {
            clipLines(geometry, newGeometry, k1, k2, axis, true);

        } else if (type === 'MultiPolygon') {
            for (var j = 0; j < geometry.length; j++) {
                var polygon = [];
                clipLines(geometry[j], polygon, k1, k2, axis, true);
                if (polygon.length) {
                    newGeometry.push(polygon);
                }
            }
        }

        if (newGeometry.length) {
            if (options.lineMetrics && type === 'LineString') {
                for (j = 0; j < newGeometry.length; j++) {
                    clipped.push(createFeature(feature.id, type, newGeometry[j], feature.tags));
                }
                continue;
            }

            if (type === 'LineString' || type === 'MultiLineString') {
                if (newGeometry.length === 1) {
                    type = 'LineString';
                    newGeometry = newGeometry[0];
                } else {
                    type = 'MultiLineString';
                }
            }
            if (type === 'Point' || type === 'MultiPoint') {
                type = newGeometry.length === 3 ? 'Point' : 'MultiPoint';
            }

            clipped.push(createFeature(feature.id, type, newGeometry, feature.tags));
        }
    }

    return clipped.length ? clipped : null;
}

function clipPoints(geom, newGeom, k1, k2, axis) {
    for (var i = 0; i < geom.length; i += 3) {
        var a = geom[i + axis];

        if (a >= k1 && a <= k2) {
            newGeom.push(geom[i]);
            newGeom.push(geom[i + 1]);
            newGeom.push(geom[i + 2]);
        }
    }
}

function clipLine(geom, newGeom, k1, k2, axis, isPolygon, trackMetrics) {

    var slice = newSlice(geom);
    var intersect = axis === 0 ? intersectX : intersectY;
    var len = geom.start;
    var segLen, t;

    for (var i = 0; i < geom.length - 3; i += 3) {
        var ax = geom[i];
        var ay = geom[i + 1];
        var az = geom[i + 2];
        var bx = geom[i + 3];
        var by = geom[i + 4];
        var a = axis === 0 ? ax : ay;
        var b = axis === 0 ? bx : by;
        var exited = false;

        if (trackMetrics) segLen = Math.sqrt(Math.pow(ax - bx, 2) + Math.pow(ay - by, 2));

        if (a < k1) {
            // ---|-->  | (line enters the clip region from the left)
            if (b > k1) {
                t = intersect(slice, ax, ay, bx, by, k1);
                if (trackMetrics) slice.start = len + segLen * t;
            }
        } else if (a > k2) {
            // |  <--|--- (line enters the clip region from the right)
            if (b < k2) {
                t = intersect(slice, ax, ay, bx, by, k2);
                if (trackMetrics) slice.start = len + segLen * t;
            }
        } else {
            addPoint(slice, ax, ay, az);
        }
        if (b < k1 && a >= k1) {
            // <--|---  | or <--|-----|--- (line exits the clip region on the left)
            t = intersect(slice, ax, ay, bx, by, k1);
            exited = true;
        }
        if (b > k2 && a <= k2) {
            // |  ---|--> or ---|-----|--> (line exits the clip region on the right)
            t = intersect(slice, ax, ay, bx, by, k2);
            exited = true;
        }

        if (!isPolygon && exited) {
            if (trackMetrics) slice.end = len + segLen * t;
            newGeom.push(slice);
            slice = newSlice(geom);
        }

        if (trackMetrics) len += segLen;
    }

    // add the last point
    var last = geom.length - 3;
    ax = geom[last];
    ay = geom[last + 1];
    az = geom[last + 2];
    a = axis === 0 ? ax : ay;
    if (a >= k1 && a <= k2) addPoint(slice, ax, ay, az);

    // close the polygon if its endpoints are not the same after clipping
    last = slice.length - 3;
    if (isPolygon && last >= 3 && (slice[last] !== slice[0] || slice[last + 1] !== slice[1])) {
        addPoint(slice, slice[0], slice[1], slice[2]);
    }

    // add the final slice
    if (slice.length) {
        newGeom.push(slice);
    }
}

function newSlice(line) {
    var slice = [];
    slice.size = line.size;
    slice.start = line.start;
    slice.end = line.end;
    return slice;
}

function clipLines(geom, newGeom, k1, k2, axis, isPolygon) {
    for (var i = 0; i < geom.length; i++) {
        clipLine(geom[i], newGeom, k1, k2, axis, isPolygon, false);
    }
}

function addPoint(out, x, y, z) {
    out.push(x);
    out.push(y);
    out.push(z);
}

function intersectX(out, ax, ay, bx, by, x) {
    var t = (x - ax) / (bx - ax);
    out.push(x);
    out.push(ay + (by - ay) * t);
    out.push(1);
    return t;
}

function intersectY(out, ax, ay, bx, by, y) {
    var t = (y - ay) / (by - ay);
    out.push(ax + (bx - ax) * t);
    out.push(y);
    out.push(1);
    return t;
}

function wrap(features, options) {
    var buffer = options.buffer / options.extent;
    var merged = features;
    var left  = clip(features, 1, -1 - buffer, buffer,     0, -1, 2, options); // left world copy
    var right = clip(features, 1,  1 - buffer, 2 + buffer, 0, -1, 2, options); // right world copy

    if (left || right) {
        merged = clip(features, 1, -buffer, 1 + buffer, 0, -1, 2, options) || []; // center world copy

        if (left) merged = shiftFeatureCoords(left, 1).concat(merged); // merge left into center
        if (right) merged = merged.concat(shiftFeatureCoords(right, -1)); // merge right into center
    }

    return merged;
}

function shiftFeatureCoords(features, offset) {
    var newFeatures = [];

    for (var i = 0; i < features.length; i++) {
        var feature = features[i],
            type = feature.type;

        var newGeometry;

        if (type === 'Point' || type === 'MultiPoint' || type === 'LineString') {
            newGeometry = shiftCoords(feature.geometry, offset);

        } else if (type === 'MultiLineString' || type === 'Polygon') {
            newGeometry = [];
            for (var j = 0; j < feature.geometry.length; j++) {
                newGeometry.push(shiftCoords(feature.geometry[j], offset));
            }
        } else if (type === 'MultiPolygon') {
            newGeometry = [];
            for (j = 0; j < feature.geometry.length; j++) {
                var newPolygon = [];
                for (var k = 0; k < feature.geometry[j].length; k++) {
                    newPolygon.push(shiftCoords(feature.geometry[j][k], offset));
                }
                newGeometry.push(newPolygon);
            }
        }

        newFeatures.push(createFeature(feature.id, type, newGeometry, feature.tags));
    }

    return newFeatures;
}

function shiftCoords(points, offset) {
    var newPoints = [];
    newPoints.size = points.size;

    if (points.start !== undefined) {
        newPoints.start = points.start;
        newPoints.end = points.end;
    }

    for (var i = 0; i < points.length; i += 3) {
        newPoints.push(points[i] + offset, points[i + 1], points[i + 2]);
    }
    return newPoints;
}

// Transforms the coordinates of each feature in the given tile from
// mercator-projected space into (extent x extent) tile space.
function transformTile(tile, extent) {
    if (tile.transformed) return tile;

    var z2 = 1 << tile.z,
        tx = tile.x,
        ty = tile.y,
        i, j, k;

    for (i = 0; i < tile.features.length; i++) {
        var feature = tile.features[i],
            geom = feature.geometry,
            type = feature.type;

        feature.geometry = [];

        if (type === 1) {
            for (j = 0; j < geom.length; j += 2) {
                feature.geometry.push(transformPoint(geom[j], geom[j + 1], extent, z2, tx, ty));
            }
        } else {
            for (j = 0; j < geom.length; j++) {
                var ring = [];
                for (k = 0; k < geom[j].length; k += 2) {
                    ring.push(transformPoint(geom[j][k], geom[j][k + 1], extent, z2, tx, ty));
                }
                feature.geometry.push(ring);
            }
        }
    }

    tile.transformed = true;

    return tile;
}

function transformPoint(x, y, extent, z2, tx, ty) {
    return [
        Math.round(extent * (x * z2 - tx)),
        Math.round(extent * (y * z2 - ty))];
}

function createTile(features, z, tx, ty, options) {
    var tolerance = z === options.maxZoom ? 0 : options.tolerance / ((1 << z) * options.extent);
    var tile = {
        features: [],
        numPoints: 0,
        numSimplified: 0,
        numFeatures: 0,
        source: null,
        x: tx,
        y: ty,
        z: z,
        transformed: false,
        minX: 2,
        minY: 1,
        maxX: -1,
        maxY: 0
    };
    for (var i = 0; i < features.length; i++) {
        tile.numFeatures++;
        addFeature(tile, features[i], tolerance, options);

        var minX = features[i].minX;
        var minY = features[i].minY;
        var maxX = features[i].maxX;
        var maxY = features[i].maxY;

        if (minX < tile.minX) tile.minX = minX;
        if (minY < tile.minY) tile.minY = minY;
        if (maxX > tile.maxX) tile.maxX = maxX;
        if (maxY > tile.maxY) tile.maxY = maxY;
    }
    return tile;
}

function addFeature(tile, feature, tolerance, options) {

    var geom = feature.geometry,
        type = feature.type,
        simplified = [];

    if (type === 'Point' || type === 'MultiPoint') {
        for (var i = 0; i < geom.length; i += 3) {
            simplified.push(geom[i]);
            simplified.push(geom[i + 1]);
            tile.numPoints++;
            tile.numSimplified++;
        }

    } else if (type === 'LineString') {
        addLine(simplified, geom, tile, tolerance, false, false);

    } else if (type === 'MultiLineString' || type === 'Polygon') {
        for (i = 0; i < geom.length; i++) {
            addLine(simplified, geom[i], tile, tolerance, type === 'Polygon', i === 0);
        }

    } else if (type === 'MultiPolygon') {

        for (var k = 0; k < geom.length; k++) {
            var polygon = geom[k];
            for (i = 0; i < polygon.length; i++) {
                addLine(simplified, polygon[i], tile, tolerance, true, i === 0);
            }
        }
    }

    if (simplified.length) {
        var tags = feature.tags || null;
        if (type === 'LineString' && options.lineMetrics) {
            tags = {};
            for (var key in feature.tags) tags[key] = feature.tags[key];
            tags['mapbox_clip_start'] = geom.start / geom.size;
            tags['mapbox_clip_end'] = geom.end / geom.size;
        }
        var tileFeature = {
            geometry: simplified,
            type: type === 'Polygon' || type === 'MultiPolygon' ? 3 :
                type === 'LineString' || type === 'MultiLineString' ? 2 : 1,
            tags: tags
        };
        if (feature.id !== null) {
            tileFeature.id = feature.id;
        }
        tile.features.push(tileFeature);
    }
}

function addLine(result, geom, tile, tolerance, isPolygon, isOuter) {
    var sqTolerance = tolerance * tolerance;

    if (tolerance > 0 && (geom.size < (isPolygon ? sqTolerance : tolerance))) {
        tile.numPoints += geom.length / 3;
        return;
    }

    var ring = [];

    for (var i = 0; i < geom.length; i += 3) {
        if (tolerance === 0 || geom[i + 2] > sqTolerance) {
            tile.numSimplified++;
            ring.push(geom[i]);
            ring.push(geom[i + 1]);
        }
        tile.numPoints++;
    }

    if (isPolygon) rewind(ring, isOuter);

    result.push(ring);
}

function rewind(ring, clockwise) {
    var area = 0;
    for (var i = 0, len = ring.length, j = len - 2; i < len; j = i, i += 2) {
        area += (ring[i] - ring[j]) * (ring[i + 1] + ring[j + 1]);
    }
    if (area > 0 === clockwise) {
        for (i = 0, len = ring.length; i < len / 2; i += 2) {
            var x = ring[i];
            var y = ring[i + 1];
            ring[i] = ring[len - 2 - i];
            ring[i + 1] = ring[len - 1 - i];
            ring[len - 2 - i] = x;
            ring[len - 1 - i] = y;
        }
    }
}

function geojsonvt(data, options) {
    return new GeoJSONVT(data, options);
}

function GeoJSONVT(data, options) {
    options = this.options = extend(Object.create(this.options), options);

    var debug = options.debug;

    if (debug) console.time('preprocess data');

    if (options.maxZoom < 0 || options.maxZoom > 24) throw new Error('maxZoom should be in the 0-24 range');
    if (options.promoteId && options.generateId) throw new Error('promoteId and generateId cannot be used together.');

    var features = convert(data, options);

    this.tiles = {};
    this.tileCoords = [];

    if (debug) {
        console.timeEnd('preprocess data');
        console.log('index: maxZoom: %d, maxPoints: %d', options.indexMaxZoom, options.indexMaxPoints);
        console.time('generate tiles');
        this.stats = {};
        this.total = 0;
    }

    features = wrap(features, options);

    // start slicing from the top tile down
    if (features.length) this.splitTile(features, 0, 0, 0);

    if (debug) {
        if (features.length) console.log('features: %d, points: %d', this.tiles[0].numFeatures, this.tiles[0].numPoints);
        console.timeEnd('generate tiles');
        console.log('tiles generated:', this.total, JSON.stringify(this.stats));
    }
}

GeoJSONVT.prototype.options = {
    maxZoom: 14,            // max zoom to preserve detail on
    indexMaxZoom: 5,        // max zoom in the tile index
    indexMaxPoints: 100000, // max number of points per tile in the tile index
    tolerance: 3,           // simplification tolerance (higher means simpler)
    extent: 4096,           // tile extent
    buffer: 64,             // tile buffer on each side
    lineMetrics: false,     // whether to calculate line metrics
    promoteId: null,        // name of a feature property to be promoted to feature.id
    generateId: false,      // whether to generate feature ids. Cannot be used with promoteId
    debug: 0                // logging level (0, 1 or 2)
};

GeoJSONVT.prototype.splitTile = function (features, z, x, y, cz, cx, cy) {

    var stack = [features, z, x, y],
        options = this.options,
        debug = options.debug;

    // avoid recursion by using a processing queue
    while (stack.length) {
        y = stack.pop();
        x = stack.pop();
        z = stack.pop();
        features = stack.pop();

        var z2 = 1 << z,
            id = toID(z, x, y),
            tile = this.tiles[id];

        if (!tile) {
            if (debug > 1) console.time('creation');

            tile = this.tiles[id] = createTile(features, z, x, y, options);
            this.tileCoords.push({z: z, x: x, y: y});

            if (debug) {
                if (debug > 1) {
                    console.log('tile z%d-%d-%d (features: %d, points: %d, simplified: %d)',
                        z, x, y, tile.numFeatures, tile.numPoints, tile.numSimplified);
                    console.timeEnd('creation');
                }
                var key = 'z' + z;
                this.stats[key] = (this.stats[key] || 0) + 1;
                this.total++;
            }
        }

        // save reference to original geometry in tile so that we can drill down later if we stop now
        tile.source = features;

        // if it's the first-pass tiling
        if (!cz) {
            // stop tiling if we reached max zoom, or if the tile is too simple
            if (z === options.indexMaxZoom || tile.numPoints <= options.indexMaxPoints) continue;

        // if a drilldown to a specific tile
        } else {
            // stop tiling if we reached base zoom or our target tile zoom
            if (z === options.maxZoom || z === cz) continue;

            // stop tiling if it's not an ancestor of the target tile
            var m = 1 << (cz - z);
            if (x !== Math.floor(cx / m) || y !== Math.floor(cy / m)) continue;
        }

        // if we slice further down, no need to keep source geometry
        tile.source = null;

        if (features.length === 0) continue;

        if (debug > 1) console.time('clipping');

        // values we'll use for clipping
        var k1 = 0.5 * options.buffer / options.extent,
            k2 = 0.5 - k1,
            k3 = 0.5 + k1,
            k4 = 1 + k1,
            tl, bl, tr, br, left, right;

        tl = bl = tr = br = null;

        left  = clip(features, z2, x - k1, x + k3, 0, tile.minX, tile.maxX, options);
        right = clip(features, z2, x + k2, x + k4, 0, tile.minX, tile.maxX, options);
        features = null;

        if (left) {
            tl = clip(left, z2, y - k1, y + k3, 1, tile.minY, tile.maxY, options);
            bl = clip(left, z2, y + k2, y + k4, 1, tile.minY, tile.maxY, options);
            left = null;
        }

        if (right) {
            tr = clip(right, z2, y - k1, y + k3, 1, tile.minY, tile.maxY, options);
            br = clip(right, z2, y + k2, y + k4, 1, tile.minY, tile.maxY, options);
            right = null;
        }

        if (debug > 1) console.timeEnd('clipping');

        stack.push(tl || [], z + 1, x * 2,     y * 2);
        stack.push(bl || [], z + 1, x * 2,     y * 2 + 1);
        stack.push(tr || [], z + 1, x * 2 + 1, y * 2);
        stack.push(br || [], z + 1, x * 2 + 1, y * 2 + 1);
    }
};

GeoJSONVT.prototype.getTile = function (z, x, y) {
    var options = this.options,
        extent = options.extent,
        debug = options.debug;

    if (z < 0 || z > 24) return null;

    var z2 = 1 << z;
    x = ((x % z2) + z2) % z2; // wrap tile x coordinate

    var id = toID(z, x, y);
    if (this.tiles[id]) return transformTile(this.tiles[id], extent);

    if (debug > 1) console.log('drilling down to z%d-%d-%d', z, x, y);

    var z0 = z,
        x0 = x,
        y0 = y,
        parent;

    while (!parent && z0 > 0) {
        z0--;
        x0 = Math.floor(x0 / 2);
        y0 = Math.floor(y0 / 2);
        parent = this.tiles[toID(z0, x0, y0)];
    }

    if (!parent || !parent.source) return null;

    // if we found a parent tile containing the original geometry, we can drill down from it
    if (debug > 1) console.log('found parent tile z%d-%d-%d', z0, x0, y0);

    if (debug > 1) console.time('drilling down');
    this.splitTile(parent.source, z0, x0, y0, z, x, y);
    if (debug > 1) console.timeEnd('drilling down');

    return this.tiles[id] ? transformTile(this.tiles[id], extent) : null;
};

function toID(z, x, y) {
    return (((1 << z) * y + x) * 32) + z;
}

function extend(dest, src) {
    for (var i in src) dest[i] = src[i];
    return dest;
}

function initGeojson(source, layerID) {
  const extent = 512; // TODO: reset to 4096? Then tolerance can be default 3
  const indexParams = { extent, tolerance: 1 };
  const tileIndex = geojsonvt(source.data, indexParams);

  return function(tileCoords, callback) {
    const { z, x, y } = tileCoords;

    const tile = tileIndex.getTile(z, x, y);

    const err = (!tile || !tile.features || !tile.features.length)
      ? "ERROR in GeojsonLoader for tile z, x, y = " + [z, x, y].join(", ")
      : null;

    const layer = { type: "FeatureCollection", extent };
    if (!err) layer.features = tile.features.map(geojsonvtToJSON);

    const json = { [layerID]: layer };
    setTimeout(() => callback(err, json));

    return { abort: () => undefined };
  };
}

function geojsonvtToJSON(value) {
  const { geometry, type: typeNum, tags: properties } = value;
  if (!geometry) return value;

  const types = ["Unknown", "Point", "LineString", "Polygon"];

  const type = (geometry.length <= 1)
    ? types[typeNum]
    : "Multi" + types[typeNum];

  const coordinates =
    (type == "MultiPolygon") ? [geometry] :
    (type === "Point" || type === "LineString") ? geometry[0] :
    geometry;

  return { geometry: { type, coordinates }, properties };
}

function init(userParams) {
  const { source, defaultID } = setParams(userParams);

  return (source.type === "geojson")
    ? initGeojson(source, defaultID)
    : initMVT(source);
}

function setParams(userParams) {
  const { source, defaultID = "default" } = userParams;

  if (typeof defaultID !== "string") fail("defaultID must be a string");

  const { type, data, tiles } = source;

  if (type === "geojson") {
    if (!data || !["Feature", "FeatureCollection"].includes(data.type)) {
      fail("no valid geojson features");
    }
  } else if (type === "vector") {
    if (!Array.isArray(tiles) || !tiles.every(url => typeof url === "string")) {
      fail("no valid tile endpoints");
    }
  } else {
    fail("source.type must be geojson or vector");
  }

  return { source, defaultID };
}

function fail(message) {
  throw Error("tile-retriever: " + message);
}

export { init };