Use a TrueType font

A TrueType (or Openype) font can be used without going through a TFM or an OFM file, like in XeTeX.

The best way to do so is to use the package luaotfload, on the CTAN, and developped here: http://github.com/mpg/luaotfload/

The code shows how we can use the table of a TrueType font to produce an internal TeX font table:

\pdfoutput1
\directlua{
callback.register("define_font",
  function(name, size)
    local fonttype, f

    filename = kpse.find_file(name, "opentype fonts")
    if filename then
      fonttype = "opentype"
    else 
      filename = kpse.find_file(name, "truetype fonts")
    end
    if filename and not fonttype then
      fonttype = "truetype"
    end

    if fonttype then
      if size < 0 then
        size = (- 655.36) * size
      end
      ttffont = fontloader.to_table(fontloader.open(filename))
      if ttffont then
        f = { }
        f.name = ttffont.fontname
        f.fullname = ttffont.names[1].names.fullname
        f.parameters = { }
        f.designsize = size
        f.size = size
        direction = 0
        f.parameters.slant = 0
        f.parameters.space = size * 0.25
        f.parameters.space_stretch = 0.3 * size
        f.parameters.space_shrink = 0.1 * size
        f.parameters.x_height = 0.4 * size
        f.parameters.quad = 1.0 * size
        f.parameters.extra_space = 0
        f.characters = { }
        local mag = size / ttffont.units_per_em

        local names_of_char = { }
        for char, glyph in pairs(ttffont.map.map) do
          names_of_char[ttffont.glyphs[glyph].name] = ttffont.map.backmap[glyph]
        end

        for char, glyph in pairs(ttffont.map.map) do
          local glyph_table = ttffont.glyphs[glyph]

          f.characters[char] = {
            index = glyph,
            width = glyph_table.width * mag,
            name = glyph_table.name }
          if glyph_table.boundingbox[4] then
            f.characters[char].height = glyph_table.boundingbox[4] * mag
          end
          if glyph_table.boundingbox[2] then
            f.characters[char].depth = -glyph_table.boundingbox[2] * mag
          end

          if glyph_table.kerns then
            local kerns = { }
            for _, kern in pairs(glyph_table.kerns) do
              kerns[names_of_char[kern.char]] = kern.off * mag
            end
            f.characters[char].kerns = kerns
          end
        end
        
        f.filename = filename
        f.type = "real"
        f.format = fonttype
        f.embedding = "subset"
        f.cidinfo = {
          registry = "Adobe",
          ordering = "Identity",
          supplement = 0,
          version = 1 }
      end
    else
      f = font.read_tfm(name, size)
    end
  return f
  end)
}

The index of the f.characters table is the Unicode value, among the properties of each entry of that table we have index which is the glyph index. Using this property we get the mapping between Unicode characters and glyphs. Kerning is handled via TeX font LKP.

What is missing in the code above is better calculation of standard TeX font parameters and OpenType features.