Freetype和其他字体程序的关系（英）

conner

今天在freetype的mailinglist上看到的。希望对初学者有点帮助。

Hello,

>
> Hello everyone,
> Its been two months I got my self in to FreeType mode. I need
> answers to
> some questions. As we all have some interest in Freetype this
> should not be
> a problem.
>

OK, here is a small description that should help you answer these
questions yourself:

- FreeType is a font engine. It's purpose is to scan font files
   in order to retrieve certain info, like metrics, glyph images,
   certain kinds of tables, etc...

   It doesn't support font installation: you have to handle it a
   font file pathname or a custom input stream, it will not pick
   it up automatically from a system-wide or user-specific list
   of "font names"

   It doesn't support text layout, because this must be performed
   at a higher level: proper text layout needs font installation,
   font matching, current language knowledge, text encoding support,
   graphics rendering system/library, etc....


- FontConfig is a library providing font installation / listing /
   matching features. It currently uses FreeType 2, though this could
   change in the future since its API only optionally mentions it.

- an X11 Font Server contains a font engine, though a very primitive
   one (monochrome output only, many scalable metrics missing to the
   application developer, and more).

   The X11 Font Server also provides a font listing capability based on
   the infamous XLFD *cough* "standard". Note that the location and format
   of font files is completely hidden to X11 developers per se the spec,
   which means that the X11 Font Protocol is pretty useless for any kind
   of application that needs to perform sophisticated WYSIWYG text
   processing. (Xprint is a joke, though it's useful for legacy applications).

   That's also why some applications, like FrameMaker or Applix come
   with their own deeply customized font server. That's also why OpenOffice
   comes with its own font engine and fonts as well

- libXFT2 is a library that uses FreeType as a font engine, and FontConfig
   for installation / matching. It's also capable of rendering anti-aliased
   and LCD-optimized text to an X11 window (something the core X11 server
   cannot do). It's capable of using the RENDER XFree86 extension within
   the server when available, but doesn't require it. It's really very
   convenient for X11 Developers. Moreover, unlike an X11 Font Server,
   it allows you to retrieve information from the font files with
   FreeType

- Pango is a text layout engine. It supports several font engines and
   font installation schemes. For instance, it can be compiled to support
   the following systems:

      Description            Font Engine           Font Lister

      X11                    X11 Font Server        X11 Font Server
      Windows                Win32 GDI              Win32 GDI
      FreeType               FreeType               Pango's own font listing (?)
      Xft                    LibXft2 (=> FreeType)  LibXft2 (=>FontConfig)

   that's a very simplified view of a very complex library. I'm pretty certain
   that Owen could give you more information. I suspect for example that the
   "Xft" sub-system is capable of using either LibXft1 or LibXft2.

   The Pango API is sufficiently abstract that a typical developer should never
   need to dwelve into the FreeType internals to properly layout & render
   internationalized text with it.


I will not answer anything about greatness or usefulness, since this really
depends on what you want to do. However, there are no plans to provide
listing/matching and text layout within FreeType, since these items were
precisely omitted from the library *by design*.

Hope this helps,

- David Turner
- The FreeType Project  (www.freetype.org)


> 1. What is the greatness of Freetype over Pango?
>
> 2. How is Freetype superior to libXFt2 and X11 font server?
>
> 3. What functionality of Freetype does Pango, libXFt2 and X11
> font server
> use?
>
> 4. What will be the advantage of building a language support system
> ((similar to that of pango) for Freetype when pango already
> provides that?
>
>  
> Please do reply. Hoping to get some good info ;)
>
> Thanks
>
> Aamir
>
> -----Original Message-----
> From: Jungshik Shin [mailto:[email protected]]
> Sent: Thursday, October 30, 2003 10:22 PM
> To: [email protected]
> Subject: Re: [Freetype] Face Familly Checking
>
> Jean Le Feuvre wrote:
> >>>FontConfig uses FreeType as far as I know, so using it will be
> >>>as slow as the solution he's currently using.
>
> >>It does cache the results, which makes it faster when you
> use the same
> >>font files more than once.
>
> That was my point.
>
> > True also, but my app is already performing font caching
> for reused font
> > files.
>
>    Where? In memory or in ext. file. fontconfig cache it in
> ext.files so
> that cache is 'persistent' across application runs.
>
> Jungshik
>
>