[Devel] Support for user-synthesized cmaps

[Vincent Caron]

Hello,

  I have implemented a support for synthesized cmaps in my own
application : I'm basically invoking iconv() when the font does not
provide a cmap matching the current locale. However I feel I'm
reinventing the wheel, and of course squarer :). I end up with encoding
lookup and cache problems that are already smartly solved by FreeType
itself. I was wondering if adding some support to help the user add
easily its own synthesized cmaps to the current face object is a good
idea. IMHO it would greatly simplify the tedious locale/cmap mathing on
user side, while reusing a bunch of FreeType components (cmap and cache
infrastructures).

An example :

typedef FT_Uint32 (*FT_CMap_Callback)(FT_Uint32);

FT_Error
FT_CMap_Synthesize (FT_Face* face,
                    FT_CMap_Callback callback,
                    FT_Encoding* user_encoding);

This would create a generic cmap class (using a resized array or a
FT_Uint32 hash), then invoke the callback for every glyph to populate
the synthesized cmap. The callback accepts a char code from the face
selected encoding and should return the equivalent char code wrt. user
encoding. This function would return a dynamically encoding ID (since
FT_Encoding is currently an enum, this is not correct) that you would
just select later.