Re: [ft] Windows font driver Parser

[Werner LEMBERG]

> I found this internal Freetype document
> 
> http://www.fifi.org/doc/libfreetype6/freetype2/

Ah, a very old version of

  https://www.freetype.org/freetype2/docs/design/index.html

(I provided the link already in a previous e-mail).

It seems that the old document contains slightly more information than
the new one.  However, I have no time currently to extend the new
version, and I invite you to work on this – from experience I know
that writing documentation *greatly* enhances the understanding (no
joke).

> It looks helpful but still no clue of how to understand the code
> flow and how can we write our own driver module.  I started windows
> font driver as told that its the simplest but unable to figure it
> out that how it works.

You have to ask more specific questions, sorry.

> 1) On base layer i.e. in src/base directory there are different high
>    level, low level APIs, font specific features with individual
>    driver module APIs.  So when are these Driver module APIs called
>    like in case of windows font driver when this ftwinfnt.c is
>    invoked.

The central structure used for communication between the base layer
and a module is `FT_Module' (what a surprise :-), which points to
`FT_ModuleRec' in `internal/ftobjs.h'.  A module gets described with
`FT_Module_Class', which provides the generic routines.  The more
specialized modules are derived from FT_Module_Class (by appending
data to it), cf. `FT_Renderer_Class' or `FT_Driver_ClassRec'.  Have a
look into file `config/ftmodule.h' for an overview.

> 2) Are driver modules only called by ftobjs.c where it checks which
>    driver to choose and than the driver who successfully parses the
>    font file is selected?

No.  For example, the TrueType font driver function `tt_face_init'
calls `sfnt->init_face' (which expands to `sfnt_init_face'), since the
basic SFNT capabilities shared between TTFs and OTFs are in the
separate `sfnt' module.


    Werner