The FT_Get_X11_Font_Format() function can be used to return a string describing the format of the font face referenced by face.
Note that this information is not needed normally; however, there are special cases (like in PDF devices) where it is important to differentiate, in spite of FreeType's uniform API.
function returns return a string describing the format of a given face,
using values which can be used as an X11 FONT_PROPERTY.
Possible values are TrueType,
Type 1, BDF,
PCF, Type 42,
CID Type 1, CFF,
PFR, and Windows FNT.
In case of an error,
NULL is returned.