scratch-svg-renderer/src/font-inliner.js

SVG renderer for Scratch

/**
 * @fileOverview Import bitmap data into Scratch 3.0, resizing image as necessary.
 */
const {FONTS} = require('scratch-render-fonts');

/**
 * Given SVG data, inline the fonts. This allows them to be rendered correctly when set
 * as the source of an HTMLImageElement. Here is a note from tmickel:
 *   // Inject fonts that are needed.
 *   // It would be nice if there were another way to get the SVG-in-canvas
 *   // to render the correct font family, but I couldn't find any other way.
 *   // Other things I tried:
 *   // Just injecting the font-family into the document: no effect.
 *   // External stylesheet linked to by SVG: no effect.
 *   // Using a <link> or <style>@import</style> to link to font-family
 *   // injected into the document: no effect.
 * @param {string} svgString The string representation of the svg to modify
 * @return {string} The svg with any needed fonts inlined
 */
const inlineSvgFonts = function (svgString) {
    // Make it clear that this function only operates on strings.
    // If we don't explicitly throw this here, the function silently fails.
    if (typeof svgString !== 'string') {
        throw new Error('SVG to be inlined is not a string');
    }

    // Collect fonts that need injection.
    const fontsNeeded = new Set();
    const fontRegex = /font-family="([^"]*)"/g;
    let matches = fontRegex.exec(svgString);
    while (matches) {
        fontsNeeded.add(matches[1]);
        matches = fontRegex.exec(svgString);
    }
    if (fontsNeeded.size > 0) {
        let str = '<defs><style>';
        for (const font of fontsNeeded) {
            if (FONTS.hasOwnProperty(font)) {
                str += `${FONTS[font]}`;
            }
        }
        str += '</style></defs>';
        svgString = svgString.replace(/<svg[^>]*>/, `$&${str}`);
        return svgString;
    }
    return svgString;
};

module.exports = inlineSvgFonts;