fix_os2_metrics.rb

require 'json'

require 'rubygems'

require 'ttfunk'

def metrics_for_file(filename)
  file = TTFunk::File.open(filename)

  max_height = 0
  max_depth = 0

  file.cmap.unicode[0].code_map.sort.each do |u, g|
    glyph = file.glyph_outlines.for(g)
    if glyph
      max_height = [max_height, glyph.y_max].max
      max_depth = [-glyph.y_min, max_depth].max
    end

  end

  return [max_height, max_depth]
end

font_dir = File.join(File.dirname(__FILE__), 'static/fonts/')

%w[Main-Regular Math-Italic AMS-Regular
   Size1-Regular Size2-Regular Size3-Regular Size4-Regular].each do |face|
  file_name = File.join(font_dir, 'KaTeX_%s.ttf' % face)

  ascent, descent = metrics_for_file(file_name)

  `./modify_ascent_descent.py #{file_name} #{ascent} #{descent}`
end

modify_ascent_descent.py

#!/usr/bin/env python2

import fontforge

import sys

if len(sys.argv) < 4:
    print "Usage: %s <font file> <ascent> <descent>" % sys.argv[0]
    sys.exit(1)

font_file = sys.argv[1]
ascent = int(sys.argv[2])
descent = int(sys.argv[3])

font = fontforge.open(font_file)

font.os2_winascent = ascent
font.os2_windescent = descent

font.hhea_ascent = ascent
font.hhea_descent = -descent

font.generate(font_file, flags=("TeX-table"))