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[bpt/emacs.git] / admin / notes / font-backend

Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
  Free Software Foundation, Inc.
See the end of the file for license conditions.


New font handling mechanism with font backend method
----------------------------------------------------

The configure script, if invoked with "--enable-font-backend", checks
if libraries freetype and fontconfig exist.  If they are both
available, macro "USE_FONT_BACKEND" is defined in src/config.h.  In
that case, the existence of Xft library is checked too.

The new files are:
	font.h -- header providing font-backend related structures
		(most important ones are "struct font" and "struct
		font_driver"), macros, and etc.
	font.c -- main font handling code.
	xfont.c -- font-driver on X for X core fonts.
	ftfont.c -- generic font-driver for FreeType fonts providing
		device-independent methods of struct font_driver.
	xftfont.c -- font-driver on X using Xft for FreeType fonts
		utilizing methods provided by ftfont.c.
	ftxfont.c -- font-driver on X directly using FreeType fonts
		utilizing methods provided by ftfont.c.
	w32font.c -- font driver on w32 using Windows native fonts,
		corresponding to xfont.c
	w32uniscribe.c -- font driver on w32, using the uniscribe API
	        to provide complex script support for opentype fonts on
		Windows 2000 and later, or earlier versions of Windows
		with uniscribe installed as an add-on.

So we already have codes for X and w32.  For Mac it seems that we need
these files:
	atmfont.c -- font-driver on mac using ATM fonts, corresponding
		to xfont.c
As BDF fonts are currently used on w32, we may also implement these:
	bdffont.c -- generic font-driver for BDF fonts, corresponding to
		ftfont.c
	bdfw32font.c -- font-driver on w32 using BDF fonts,
		corresponding to ftxfont.c
But, as FreeType already supports BDF fonts, if FreeType and
Fontconfig are also available on w32, what we need may be:
	ftw32font.c -- font-driver on w32 directly using FreeType fonts
		utilizing methods provided by ftfont.c.

And, for those to work, macterm.c and macfns.c must be changed by the
similar way as xterm.c and xfns.c (the parts "#ifdef USE_FONT_BACKEND"
... "#endif" should be checked).

It may be interesting if Emacs supports a frame buffer directly and
has these font driver.
	ftfbfont.c -- font-driver on FB for FreeType fonts.
	bdffbfont.c -- font-driver on FB for BDF fonts.

Note: The fontset related codes are not yet matured to work well with
the font backend method.  So, for instance, even if you start Emacs
as something like this:
  % emacs -fn tahoma
Non-ASCII Latin characters will not be displayed by the font "tahoma".
In such a case, please try this:

(set-fontset-font "fontset-default" 'latin '("tahoma" . "unicode-bmp"))

\f
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