[ft] Positive or negative bitmap pitch

[Crend King]

Hello. I would like to know when do functions such as FT_Glyph_To_Bitmap return 
bitmap with positive and negative pitch. In my experience, most time the pitch 
is positive, meaning a top-down flow. I also looked up source code. In 
ftbitmap.c, I found "if ( pitch < 0 ) pitch = -pitch;", also indicating a 
positive pitch. My project mostly deals with TrueType fonts, so if I know the 
pitch is always positive in this situation, I could simplify the algorithm.

Thanks a lot!