FcFreeTypeCharSet − compute Unicode coverage
FcCharSet * FcFreeTypeCharSet (FT_Face face, FcBlanks *blanks);
Scans a FreeType face and returns the set of encoded Unicode chars. This scans several encoding tables to build as complete a list as possible. If ’blanks’ is not 0, the glyphs in the font are examined and any blank glyphs not in ’blanks’ are not placed in the returned FcCharSet.