fontpath-util/index.js

Some simple utils for handling font sizes

// module.exports.pointsToPixels = function(pointSize, resolution) {
// 	resolution = typeof resolution === "number" ? resolution : 72;
// 	return pointSize * resolution / 72;
// };

// module.exports.coordToPixel = function(coord, pixelSize, emSize) {
// 	emSize = typeof emSize === "number" ? emSize : 2048;
// 	return coord * pixelSize / emSize;
// };

/**
 * Converts a pt size to px size, namely useful for matching
 * size with CSS styles. If no DPI is specified, 96 is assumed
 * (as it leads to correct rendering in all browsers).
 * 
 * @param  {Number} fontSize the desired font size in points
 * @param  {Number} dpi      the expected DPI, generally 96 for browsers
 * @return {Number}          the rounded pixel font size
 */
module.exports.pointToPixel = function(fontSize, dpi) {
    dpi = dpi||dpi===0 ? dpi : 96;
    fontSize = fontSize * dpi / 72;
    return Math.round(fontSize);
};

/**
 * For the given font and (pixel) font size, this method returns the
 * scale that will need to be applied to EM units (i.e. font paths) 
 * to have the font render at the expected size (i.e. to match the browser).
 *
 * If no font size is specified, we will use the default font size (which is in points)
 * and convert it to pixels. 
 * 
 * @param  {Font} font     a font object from the fontpath tool
 * @param  {Number} fontSize the desired font size, defaults to the font's default size
 * @return {Number} returns the scale for this font size         
 */
module.exports.getPxScale = function(font, fontSize) {
    if (font.bitmap)
        return 1.0;

    //If no fontSize is specified, it will just fall back to using the font's own size with 96 DPI.
    fontSize = typeof fontSize === "number" ? fontSize : this.pointToPixel(font.size);

    //Takes in a font size in PIXELS and gives us the expected scaling factor
    var sz = font.units_per_EM/64;
    sz = (sz/font.size * fontSize);

    return ((font.resolution * 1/72 * sz) / font.units_per_EM);
};

/**
 * For the given font and (point) font size, this method returns the
 * scale that will need to be applied to EM units (i.e. font paths) 
 * to have the font render at the expected size (i.e. to match the browser).
 * 
 * If no font size is specified, we will use the default font size.
 * 
 * @param  {Font} font       a font object from the fontpath tool
 * @param  {Number} fontSize the desired font size, defaults to the font's default size
 * @return {Number}          the scale for this font size
 */
module.exports.getPtScale = function(font, fontSize) {
    fontSize = typeof fontSize === "number" ? fontSize : font.size;
    fontSize = this.pointToPixel(fontSize);
    return this.getPxScale(font, fontSize);
};