maplibre-gl/src/render/glyph_atlas.ts

BSD licensed community fork of mapbox-gl, a WebGL interactive maps library

import {AlphaImage} from '../util/image';
import {register} from '../util/web_worker_transfer';
import potpack from 'potpack';

import type {GlyphMetrics, StyleGlyph} from '../style/style_glyph';

const padding = 1;

export type Rect = {
    x: number;
    y: number;
    w: number;
    h: number;
};

export type GlyphPosition = {
    rect: Rect;
    metrics: GlyphMetrics;
};

export type GlyphPositions = {
    [_: string]: {
        [_: number]: GlyphPosition;
    };
};

export default class GlyphAtlas {
    image: AlphaImage;
    positions: GlyphPositions;

    constructor(stacks: {
        [_: string]: {
            [_: number]: StyleGlyph;
        };
    }) {
        const positions = {};
        const bins = [];

        for (const stack in stacks) {
            const glyphs = stacks[stack];
            const stackPositions = positions[stack] = {};

            for (const id in glyphs) {
                const src = glyphs[+id];
                if (!src || src.bitmap.width === 0 || src.bitmap.height === 0) continue;

                const bin = {
                    x: 0,
                    y: 0,
                    w: src.bitmap.width + 2 * padding,
                    h: src.bitmap.height + 2 * padding
                };
                bins.push(bin);
                stackPositions[id] = {rect: bin, metrics: src.metrics};
            }
        }

        const {w, h} = potpack(bins);
        const image = new AlphaImage({width: w || 1, height: h || 1});

        for (const stack in stacks) {
            const glyphs = stacks[stack];

            for (const id in glyphs) {
                const src = glyphs[+id];
                if (!src || src.bitmap.width === 0 || src.bitmap.height === 0) continue;
                const bin = positions[stack][id].rect;
                AlphaImage.copy(src.bitmap, image, {x: 0, y: 0}, {x: bin.x + padding, y: bin.y + padding}, src.bitmap);
            }
        }

        this.image = image;
        this.positions = positions;
    }
}

register('GlyphAtlas', GlyphAtlas);