Re: what is the status of the XFT branch?

[Kenichi Handa]

In article <address@hidden>, Jan Djärv <address@hidden> writes:

> Pedro Kröger wrote:
>> Hi,
>> 
>> I just compiled the xft branch of emacs and it's amazing! But I've read
>> it's not maintained any more. Some emails mentioned a merge of the xft
>> branch with the unicode one. So I'd like to ask: what is the status of
>> the xft support in emacs? is there any branch with it been maintained?
>> 

> It is not maintained, because we need to move to unicode, so the unicode-xft 
> branch will be maintained.  However, don't expect much to happen before the 
> upcoming Emacs release.

Actually, after reading codes of XFT branch, I started to
design a new font handling mechanism.  The basic plan is to
use multiple font-backends drivers (xcore, xft, windows,
bdf, atm, etc).  The main motivation for this rewriting is
that the current XFT code in the branch is very difficult to
utilize fontconfig's help for font selection, and to drive
OTF fonts.  And also, I want to clean up the current fairly
complicated font related codes (including many HAVE_XFT
conditionals, many XLFD parsing code, etc).

But, as there are many other works to be done, the progress
for the above code is slow.  Please don't expect a quick
response on this matter.  Anyway, here's the current font.h
file (not yet fully considered) with which you may get a
feeling of the design.

---
Kenichi Handa
address@hidden

/* font.h -- Interface definition for font handling.
   Copyright (C) 2006 Free Software Foundation, Inc.
   Copyright (C) 2006
     National Institute of Advanced Industrial Science and Technology (AIST)
     Registration Number H13PRO009

This file is part of GNU Emacs.

GNU Emacs is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs; see the file COPYING.  If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.  */

#ifndef FONT_H_INCLUDED
#define FONT_H_INCLUDED

#include "ccl.h"

/* We have three concepts concerning font.

   FONT-SPEC

        Vector (length FONT_MAX_INDEX) of font properties.  Some
        properties can be left unspecified (i.e. nil).  Emacs asks
        font-drivers to find a font by FONT-SPEC.  A fontset entry
        specifies requisite properties whereas a face specifies just
        preferable properties.

   FONT-ENTITY

        Vector (length FONT_MAX_INDEX) of fully specified font
        properties that a font-driver returns upon a request of
        FONT-SPEC.

   FONT-OBJECT

        "struct font_info" corresponding to an opened font.

 */


struct font_driver;
struct font_info;

enum font_property_index
  {
    /* index                       value in spec        value in entity */
    /* FONT-TYPE is a symbol indicating font-driver; one of `x',
       `freetype', `bdf', `windows', `atm'.  See "enum font_type" for
       more info. */
    FONT_TYPE_INDEX,            /* symbol               integer */

    /* FONT-FAMILY is a family name or a combination of a foundry and
       family name.  */
    FONT_FAMILY_INDEX,          /* symbol               symbol */

    /* FONT-STYLE is a combination of weight, slant, and swidth.  It
       is possible to encode it in an integer:
         (WEIGHT << 16) | (SLANT << 8) | SWIDTH
       where WEIGHT, SLANT, SWIDTH are numbers less than 256 defined as
       FC_WEIGHT_*, FC_SLANT_*, FC_WIDTH_* macros in fontconfig.h.  */
    FONT_STYLE_INDEX,           /* symbol or integer    integer */

    /* FONT-ADSTYLE is a additional style name.  */
    FONT_ADSTYLE_INDEX,         /* symbol               symbol */

    /* FONT-SIZE is a size of the font.  If positive, it is a point
       size in the unit of 1/10 point.  If negative, its absolute
       value is a pixel size.  If zero, the font is scalable.  */
    FONT_SIZE_INDEX,            /* integer or nil       integer */

    /* FONT-REGISTRY is a combination of a registry and encoding
       name.  */
    FONT_REGISTRY_INDEX,        /* symbol               symbol */

    /* FONT-EXTRA is an alist of extra information (e.g. OpenType
       features, language coverage) about the font. */
    FONT_EXTRA_INDEX,           /* alist                alist */

    /* This value is the length of font-spec/entity vector.  */
    FONT_MAX_INDEX
  };

enum font_sort_key
  {
    FONT_SKEY_WEIGHT,
    FONT_SKEY_SLANT,
    FONT_SKEY_SWIDTH,
    FONT_SKEY_SIZE,
    FONT_SKEY_MAX
  };

enum font_type
  {
    FONT_TYPE_X,
    FONT_TYPE_FREETYPE,
    FONT_TYPE_BDF,
    FONT_TYPE_WINDOWS,
    FONT_TYPE_ATM,
    FONT_TYPE_MAX,
    FONT_TYPE_UNSPECIFIED
  };

extern Lisp_Object Qx, Qfreetype, Qbdf, Qwindows, Qatm;

extern Lisp_Object Qotf, Qlanguage;

enum font_name_type
  {
    FONT_NAME_XLFD,
    FONT_NAME_FC,
    FONT_NAME_MAX
  };


/* This data type is used for the font_table field of window system
   depending data area (e.g. struct x_display_info on X window).  */

struct font_info
{
  /* Pointer to font-driver dependent font structure.  */
  void *font;

  /* Index number of the font.  */
  int font_idx;

  /* Index number of the entity of the font.  */
  int entity_idx;

  /* Name to be used to find the font.  */
  char *name;

  /* Full name of the font given by a font driver.  */
  char *full_name;

  /* Charset to encode a character code into a glyph code of the font.
     -1 means to drive the font directly by glyph code.  */
  int charset;

#ifdef WINDOWSNT
  /* Codepage of characters that will be displayed by the font.  */
  int codepage;
#endif

  /* Maximum bound width over all existing characters of the font.
     For X core fonts, this is same as (font->max_bounds.width) */
  int size;

  /* Height of the font.  For X core fonts, this is the same as
     (font->ascent + font->descent).  */
  int height;

  /* Width of the space glyph of the font.  */
  int space_width;

  /* Average width of glyphs in the font.  */
  int average_width;

  /* 1 iff `vertical-centering-font-regexp' matches the font name.
     In this case, we render characters at vartical center positions
     of lines.  */
  int vertical_centering;

  /* Encoding type of the font.  The value is one of
     0, 1, 2, or 3:
        0: code points 0x20..0x7F or 0x2020..0x7F7F are used
        1: code points 0xA0..0xFF or 0xA0A0..0xFFFF are used
        2: code points 0x20A0..0x7FFF are used
        3: code points 0xA020..0xFF7F are used
     If the member `font_encoder' is not NULL, this member is ignored.
  */
  unsigned char encoding_type;

  /* The baseline position of a font is normally `ascent' value of the
     font.  However, there exists many fonts which don't set `ascent'
     an appropriate value to be used as baseline position.  This is
     typical in such ASCII fonts which are designed to be used with
     Chinese, Japanese, Korean characters.  When we use mixture of
     such fonts and normal fonts (having correct `ascent' value), a
     display line gets very ugly.  Since we have no way to fix it
     automatically, it is users responsibility to supply well designed
     fonts or correct `ascent' value of fonts.  But, the latter
     requires heavy work (modifying all bitmap data in BDF files).
     So, Emacs accepts a private font property
     `_MULE_BASELINE_OFFSET'.  If a font has this property, we
     calculate the baseline position by subtracting the value from
     `ascent'.  In other words, the value indicates how many bits
     higher we should draw a character of the font than normal ASCII
     text for a better looking.

     We also have to consider the fact that the concept of `baseline'
     differs among languages to which each character belongs.  For
     instance, baseline should be at the bottom most position of all
     glyphs for Chinese, Japanese, and Korean.  But, many of existing
     fonts for those characters doesn't have correct `ascent' values
     because they are designed to be used with ASCII fonts.  To
     display characters of different language on the same line, the
     best way will be to arrange them in the middle of the line.  So,
     in such a case, again, we utilize the font property
     `_MULE_BASELINE_OFFSET'.  If the value is larger than `ascent' we
     calculate baseline so that a character is arranged in the middle
     of a line.  */

  int baseline_offset;

  /* Non zero means a character should be composed at a position
     relative to the height (or depth) of previous glyphs in the
     following cases:
        (1) The bottom of the character is higher than this value.  In
        this case, the character is drawn above the previous glyphs.
        (2) The top of the character is lower than 0 (i.e. baseline
        height).  In this case, the character is drawn beneath the
        previous glyphs.

     This value is taken from a private font property
     `_MULE_RELATIVE_COMPOSE' which is introduced by Emacs.  */
  int relative_compose;

  /* Non zero means an ascent value to be used for a character
     registered in char-table `use-default-ascent'.  */
  int default_ascent;

  /* CCL program to calculate code points of the font.  */
  struct ccl_program *font_encoder;

  struct font_driver *driver;
};

struct font_metrics
{
  short lbearing, rbearing, width, ascent, descent;
};

struct font_driver
{
  /* List fonts matching with SPEC on frame F.  The value is a list
     of font-entity.  */
  Lisp_Object (*list) P_ ((FRAME_PTR f, Lisp_Object spec));

  /* Open a font specified by ENTITY with SIZE on frame F.  */
  struct font_info *(*open) P_ ((FRAME_PTR f, Lisp_Object entity, int size));

  struct font_info *(*get_info) P_ ((FRAME_PTR f, int font_idx));

  int (*check) P_ ((FRAME_PTR f, struct font_info *font));

  unsigned (*encode_char) P_ ((struct font_info *font, int c));

  int (*glyph_metric) P_ ((struct font_info *font, unsigned code,
                           struct font_metrics *metrics));

  int (*text_metric) P_ ((FRAME_PTR f, struct font_info *font,
                          unsigned *code, int nglyphs,
                          struct font_metrics *metrics));

  int (*draw) P_ ((FRAME_PTR f, struct font_info *font, void *gc,
                   int x, int y, unsigned *code, int nglyphs, int as_image));
};

extern void update_font_sort_order P_ ((int order[FONT_SKEY_MAX]));

extern Lisp_Object list_fonts P_ ((FRAME_PTR f, Lisp_Object spec));

extern void syms_of_xfont P_ (());
extern void syms_of_freetype P_ (());
extern void syms_of_bdffont P_ (());
extern void syms_of_w32font P_ (());
extern void syms_of_atmfont P_ (());

#endif  /* not FONT_H_INCLUDED */