Re: Compositing glyphs.

[David Turner]

Hi Nathan,

Nathan Hurst a écrit :
> 
> G'Day, B-)
> 
> I've been asked several times how to composite glyphs from freetype, so
> I've written my understanding up at
>
> http://www.csse.monash.edu.au/~njh/phd/ft-composition.txt
> 
> Please feel free to send me comments, or to move this onto the main
> freetype site.
> 
I think it'd be an interesting idea to provide this kind of document
on the freetype site, though a few screenshots to illustrate this
would be welcomed :-)

Other than that, I believe that the correct way to render text is
to render each line into an intermediate gray buffer, perform
saturation, then blit/compose the whole line with one of the
available composition routines, yours included.

> njh
> p.s. Is there an authoritative document on how FT2 manages memory?

What do you mean exactly ? :

  - what objects belong to the library, and which do not ?
    (especially when they're returned to client apps)

    Basically, I would say that this must be documented
    for each function call. If not, the information is
    missing..


  - how memory is managed internally ? Well, all memory
    allocations are made through FT_Alloc, FT_Realloc and
    FT_Free, that all have interesting properties:

       - the second argument is a pointer to a pointer,
         which is always set to 0 in case of error (in
         the case of allocation), or normally (in the
         case of FT_Free).

       - their first parameter is a FT_Memory handle to
         a memory manager. (see <freetype/ftsystem.h> for
         details). It's possible to plug your own manager
         by initializing the library with:

              // create memory manager
              FT_Memory  my_memory =  ....;

              // create new library instance
              error = FT_New_Library( my_memory, &library );
              if (error) ...

              // register default modules to the new library
              error = FT_Add_Default_Modules( library );
              if (error)

          this sequence replaces a FT_Init_FreeType call
          (which uses a default memory manager based on malloc/free)

          You must also finalize your library with
          FT_Done_Library() instead of FT_Done_FreeType()

   And finally, there isn't a single static or global variable
   in the code, so you can run several library instances concurrently
   (but each instance isn't thread-safe though to simplify the design
    of the engine, and more importantly, of modules).

> p.p.s. I'm going to be in Sydney for a couple of days so I may take a
> while in answering emails :-)

Have fun in Sidney :-)

Cheers,

- David