Re: [ft] FT_Open_Face with negative face_index

[David Turner]

David Osborn a écrit :
> The FreeType2 docs mention that, if the face_index parameter of 
> FT_Open_Face is negative, '* face', which I'm assuming refers to the 
> function's 'aface' parameter, will not be filled in.  See: 
> http://freetype.sourceforge.net/freetype2/docs/reference/ft2-base_interface.html#FT_Open_Face 
> (look under the 'note' heading).  This suggests that I should be able to 
> pass a null pointer as the aface parameter since its not going to be 
> used anyway.  However, the function fails if I do that, so my assumption 
> must be wrong.  If I pass it a real pointer to an FT_Face instance, it 
> fills it in even though the face_index is negative (the docs say it 
> 'will not return any face handle' in this case).  FT_Open_Face seems to 
> operate as if the face_index were 0 even if I pass -1.  The only 
> possibility I can think of is if I'm misinterpreting what '* face' means 
> in the docs.  Any suggestions?

David, the purpose of a negative face index is to be able to very 
quickly test wether a font file's format is supported by the version
of FT2 you're linking with.

If it's unsupported, the function will return an error.
If it's supported, it will return 0, and fill the FT_Face with
only a very limited set of fields (i.e. 'face->num_faces').

Regards,

- David Turner
- The FreeType Project  (www.freetype.org)