mapbox-gl/src/style/parse_glyph_pbf.js

A WebGL interactive maps library

// @flow

import {AlphaImage} from '../util/image.js';

import Protobuf from 'pbf';
const border = 3;

import type {StyleGlyph} from './style_glyph.js';

function readFontstacks(tag: number, glyphData: {glyphs: Array<StyleGlyph>, ascender?: number, descender?: number}, pbf: Protobuf) {
    glyphData.glyphs = [];
    if (tag === 1) {
        pbf.readMessage(readFontstack, glyphData);
    }
}

function readFontstack(tag: number,  glyphData: {glyphs: Array<StyleGlyph>, ascender?: number, descender?: number}, pbf: Protobuf) {
    if (tag === 3) {
        const {id, bitmap, width, height, left, top, advance} = pbf.readMessage(readGlyph, {});
        glyphData.glyphs.push({
            id,
            bitmap: new AlphaImage({
                width: width + 2 * border,
                height: height + 2 * border
            }, bitmap),
            metrics: {width, height, left, top, advance}
        });
    } else if (tag === 4) {
        glyphData.ascender = pbf.readSVarint();
    } else if (tag === 5) {
        glyphData.descender = pbf.readSVarint();
    }
}

function readGlyph(tag: number, glyph: Object, pbf: Protobuf) {
    if (tag === 1) glyph.id = pbf.readVarint();
    else if (tag === 2) glyph.bitmap = pbf.readBytes();
    else if (tag === 3) glyph.width = pbf.readVarint();
    else if (tag === 4) glyph.height = pbf.readVarint();
    else if (tag === 5) glyph.left = pbf.readSVarint();
    else if (tag === 6) glyph.top = pbf.readSVarint();
    else if (tag === 7) glyph.advance = pbf.readVarint();
}

export default function (data: ArrayBuffer | Uint8Array): {glyphs: Array<StyleGlyph>, ascender?: number, descender?: number} {
    return new Protobuf(data).readFields(readFontstacks, {});
}

export const GLYPH_PBF_BORDER = border;