[Devel] Truetype charmap matching algorithm

[stephenfung]

I am working on algorithm of 

input: unicode of character
output: the glyph of that character (ie the location of that glyph in
TTF, say)

However, as i found in the function of FT_Get_Char_Index 
[ftobjs.c (1714)]

result = cmap->clazz->char_index( cmap, charcode );

and i cannot follow the function pointer of char_index any more.

Can anyone tell me the flow of how unicode match with glyph in common
usage?

I have deal with that problem for a few weeks.... 

THX OF HELP