[Freetype] Newbie questions

[Gennady Gleizer]

Hi,

I realize my questions may sound stupid, however I couldn't find the answers
neither in documentation nor in this list archives. I'll appreciate if you
point me to appropriate sections in documentation or relevant threads of
this mailing list. I'm working on general porting of Win32 FO-to-PDF
renderer to Unix. Rendering itself is performed using PDF libraries API, but
the calculations should be done before that.
1. My system works in twips (1/1440 of an inch). What should I do with
accender/descender etc. of face->size->metrics to get those values in twips
(or, at least, device-dependent pixels) ? For now, everything I've found was
http://www.freetype.org/pipermail/freetype/2001-October/004517.html. 
2. I can not find a value for line gap (aka external leading). 
3. Where exactly should I find EM size (for internal leading calculations) ?
4. How do I convert glyph metrics to twips or pixels ?
Thanks in advance

GG