code: def com_google_fonts_check_production_glyphs_similarity(ttFont, api_gfonts_ttFont):
    
  
    def glyphs_surface_area(ttFont):
      """Calculate the surface area of a glyph's ink"""
      from fontTools.pens.areaPen import AreaPen
      glyphs = {}
      glyph_set = ttFont.getGlyphSet()
      area_pen = AreaPen(glyph_set)
  
      for glyph in glyph_set.keys():
        glyph_set[glyph].draw(area_pen)
  
        area = area_pen.value
        area_pen.value = 0
        glyphs[glyph] = area
      return glyphs
  
    bad_glyphs = []
    these_glyphs = glyphs_surface_area(ttFont)
    gfonts_glyphs = glyphs_surface_area(api_gfonts_ttFont)
  
    shared_glyphs = set(these_glyphs) & set(gfonts_glyphs)
  
    this_upm = ttFont['head'].unitsPerEm
    gfonts_upm = api_gfonts_ttFont['head'].unitsPerEm
  
    for glyph in shared_glyphs:
      # Normalize area difference against comparison's upm
      this_glyph_area = (these_glyphs[glyph] / this_upm) * gfonts_upm
      gfont_glyph_area = (gfonts_glyphs[glyph] / gfonts_upm) * this_upm
  
      if abs(this_glyph_area - gfont_glyph_area) > 7000:
        bad_glyphs.append(glyph)
  
    if bad_glyphs:
      yield WARN, ("Following glyphs differ greatly from"
                   " Google Fonts version: [{}]").format(", ".join(bad_glyphs))
    else:
      yield PASS, ("Glyphs are similar in"
                   " comparison to the Google Fonts version.")
docs: Glyphs are similiar to Google Fonts version?