mapbox-gl/src/data/load_geometry.js

A WebGL interactive maps library

'use strict';

const util = require('../util/util');
const EXTENT = require('./extent');
const assert = require('assert');


// These bounds define the minimum and maximum supported coordinate values.
// While visible coordinates are within [0, EXTENT], tiles may theoretically
// contain cordinates within [-Infinity, Infinity]. Our range is limited by the
// number of bits used to represent the coordinate.
function createBounds(bits) {
    return {
        min: -1 * Math.pow(2, bits - 1),
        max: Math.pow(2, bits - 1) - 1
    };
}

const boundsLookup = {
    15: createBounds(15),
    16: createBounds(16)
};

/**
 * Loads a geometry from a VectorTileFeature and scales it to the common extent
 * used internally.
 * @param {VectorTileFeature} feature
 * @param {number} [bits=16] The number of signed integer bits available to store
 *   each coordinate. A warning will be issued if any coordinate will not fits
 *   in the specified number of bits.
 * @private
 */
module.exports = function loadGeometry(feature, bits) {
    const bounds = boundsLookup[bits || 16];
    assert(bounds);

    const scale = EXTENT / feature.extent;
    const geometry = feature.loadGeometry();
    for (let r = 0; r < geometry.length; r++) {
        const ring = geometry[r];
        for (let p = 0; p < ring.length; p++) {
            const point = ring[p];
            // round here because mapbox-gl-native uses integers to represent
            // points and we need to do the same to avoid renering differences.
            point.x = Math.round(point.x * scale);
            point.y = Math.round(point.y * scale);

            if (point.x < bounds.min || point.x > bounds.max || point.y < bounds.min || point.y > bounds.max) {
                util.warnOnce('Geometry exceeds allowed extent, reduce your vector tile buffer size');
            }
        }
    }
    return geometry;
};