@kibeo/loaders.gl-mvt/src/lib/binary-vector-tile/vector-tile-layer.js

Loader for Mapbox Vector Tiles

// This code is forked from https://github.com/mapbox/vector-tile-js under BSD 3-clause license.

import VectorTileFeature from './vector-tile-feature.js';

export default class VectorTileLayer {
  constructor(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;
  }

  // return feature `i` from this layer as a `VectorTileFeature`
  feature(i, firstPassData) {
    if (i < 0 || i >= this._features.length) {
      throw new Error('feature index out of bounds');
    }

    this._pbf.pos = this._features[i];

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

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;
}