overstriking for bold-face

overstriking for bold-face

[Miles Bader]

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What do people think of the following patch?

It makes emacs use `overstriking' (drawing text again shifted by one
pixel) to simulate bold-face for fonts that have no bold version.  The
same technique is used by programs such as gnome-terminal.

I did this because some otherwise very nice fonts don't come with bold
versions.

[It might seem as if it would generate unreadable results (if you look
with a pixel magifier, very fine characters like `m' can become mere
blobs), but in fact it works very well in practice, and the resulting
text seems generally no less readable than non-bold text!]

-Miles


Patch:



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Index: src/dispextern.h
===================================================================
RCS file: /cvsroot/emacs/emacs/src/dispextern.h,v
retrieving revision 1.140
diff -u -r1.140 dispextern.h
*** src/dispextern.h	25 Oct 2002 06:49:15 -0000	1.140
--- src/dispextern.h	16 Nov 2002 15:10:41 -0000
***************
*** 1359,1364 ****
--- 1359,1367 ----
       realize_x_face).  */
    unsigned colors_copied_bitwise_p : 1;
  
+   /* If non-zero, use overstrike (to simulate bold-face).  */
+   unsigned overstrike : 1;
+ 
    /* Next and previous face in hash collision list of face cache.  */
    struct face *next, *prev;
  
Index: src/xfaces.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/xfaces.c,v
retrieving revision 1.265
diff -u -r1.265 xfaces.c
*** src/xfaces.c	23 Oct 2002 16:55:19 -0000	1.265
--- src/xfaces.c	16 Nov 2002 15:14:10 -0000
***************
*** 522,528 ****
  static int face_numeric_slant P_ ((Lisp_Object));
  static int face_numeric_swidth P_ ((Lisp_Object));
  static int face_fontset P_ ((Lisp_Object *));
! static char *choose_face_font P_ ((struct frame *, Lisp_Object *, int, int));
  static void merge_face_vectors P_ ((struct frame *, Lisp_Object *, Lisp_Object*, Lisp_Object));
  static void merge_face_inheritance P_ ((struct frame *f, Lisp_Object,
  					Lisp_Object *, Lisp_Object));
--- 522,528 ----
  static int face_numeric_slant P_ ((Lisp_Object));
  static int face_numeric_swidth P_ ((Lisp_Object));
  static int face_fontset P_ ((Lisp_Object *));
! static char *choose_face_font P_ ((struct frame *, Lisp_Object *, int, int, int*));
  static void merge_face_vectors P_ ((struct frame *, Lisp_Object *, Lisp_Object*, Lisp_Object));
  static void merge_face_inheritance P_ ((struct frame *f, Lisp_Object,
  					Lisp_Object *, Lisp_Object));
***************
*** 534,540 ****
  static struct face *make_realized_face P_ ((Lisp_Object *));
  static void free_realized_faces P_ ((struct face_cache *));
  static char *best_matching_font P_ ((struct frame *, Lisp_Object *,
! 				     struct font_name *, int, int));
  static void cache_face P_ ((struct face_cache *, struct face *, unsigned));
  static void uncache_face P_ ((struct face_cache *, struct face *));
  static int xlfd_numeric_slant P_ ((struct font_name *));
--- 534,540 ----
  static struct face *make_realized_face P_ ((Lisp_Object *));
  static void free_realized_faces P_ ((struct face_cache *));
  static char *best_matching_font P_ ((struct frame *, Lisp_Object *,
! 				     struct font_name *, int, int, int *));
  static void cache_face P_ ((struct face_cache *, struct face *, unsigned));
  static void uncache_face P_ ((struct face_cache *, struct face *));
  static int xlfd_numeric_slant P_ ((struct font_name *));
***************
*** 1257,1267 ****
  {
    struct font_info *font_info = NULL;
    char *font_name;
  
    face->font_info_id = -1;
    face->font = NULL;
  
!   font_name = choose_face_font (f, face->lface, face->fontset, c);
    if (!font_name)
      return;
  
--- 1257,1269 ----
  {
    struct font_info *font_info = NULL;
    char *font_name;
+   int needs_overstrike;
  
    face->font_info_id = -1;
    face->font = NULL;
  
!   font_name = choose_face_font (f, face->lface, face->fontset, c,
! 				&needs_overstrike);
    if (!font_name)
      return;
  
***************
*** 1274,1279 ****
--- 1276,1282 ----
        face->font_info_id = font_info->font_idx;
        face->font = font_info->font;
        face->font_name = font_info->full_name;
+       face->overstrike = needs_overstrike;
        if (face->gc)
  	{
  	  x_free_gc (f, face->gc);
***************
*** 4313,4319 ****
  	  /* Choose a font name that reflects LFACE's attributes and has
  	     the registry and encoding pattern specified in the default
  	     fontset (3rd arg: -1) for ASCII characters (4th arg: 0).  */
! 	  font = choose_face_font (f, XVECTOR (lface)->contents, -1, 0);
  	  if (!font)
  	    error ("No font matches the specified attribute");
  	  font_name = build_string (font);
--- 4316,4322 ----
  	  /* Choose a font name that reflects LFACE's attributes and has
  	     the registry and encoding pattern specified in the default
  	     fontset (3rd arg: -1) for ASCII characters (4th arg: 0).  */
! 	  font = choose_face_font (f, XVECTOR (lface)->contents, -1, 0, 0);
  	  if (!font)
  	    error ("No font matches the specified attribute");
  	  font_name = build_string (font);
***************
*** 6140,6154 ****
     widths if ATTRS specifies such a width.
  
     Value is a font name which is allocated from the heap.  FONTS is
!    freed by this function.  */
  
  static char *
! best_matching_font (f, attrs, fonts, nfonts, width_ratio)
       struct frame *f;
       Lisp_Object *attrs;
       struct font_name *fonts;
       int nfonts;
       int width_ratio;
  {
    char *font_name;
    struct font_name *best;
--- 6143,6162 ----
     widths if ATTRS specifies such a width.
  
     Value is a font name which is allocated from the heap.  FONTS is
!    freed by this function.
! 
!    If NEEDS_OVERSTRIKE is non-zero, a boolean is returned in it to
!    indicate whether the resulting font should be drawn using overstrike
!    to simulate bold-face.  */
  
  static char *
! best_matching_font (f, attrs, fonts, nfonts, width_ratio, needs_overstrike)
       struct frame *f;
       Lisp_Object *attrs;
       struct font_name *fonts;
       int nfonts;
       int width_ratio;
+      int *needs_overstrike;
  {
    char *font_name;
    struct font_name *best;
***************
*** 6183,6188 ****
--- 6191,6199 ----
  
    exact_p = 0;
  
+   if (needs_overstrike)
+     *needs_overstrike = 0;
+ 
    /* Start with the first non-scalable font in the list.  */
    for (i = 0; i < nfonts; ++i)
      if (!font_scalable_p (fonts + i))
***************
*** 6203,6209 ****
  	    if (exact_p)
  	      break;
  	  }
- 
      }
    else
      best = NULL;
--- 6214,6219 ----
***************
*** 6236,6241 ****
--- 6246,6269 ----
  		    && !better_font_p (specified, best, fonts + i, 0, 0)))
  	      best = fonts + i;
  	  }
+ 
+       if (needs_overstrike)
+ 	{
+ 	  enum xlfd_weight want_weight = specified[XLFD_WEIGHT];
+ 	  enum xlfd_weight got_weight = best->numeric[XLFD_WEIGHT];
+ 
+ 	  if (want_weight > XLFD_WEIGHT_MEDIUM && want_weight > got_weight)
+ 	    {
+ 	      /* We want a bold font, but didn't get one; try to use
+ 		 overstriking instead to simulate bold-face.  However,
+ 		 don't overstrike an already-bold fontn unless the
+ 		 desired weight grossly exceeds the available weight.  */
+ 	      if (got_weight > XLFD_WEIGHT_MEDIUM)
+ 		*needs_overstrike = (got_weight - want_weight) > 2;
+ 	      else
+ 		*needs_overstrike = 1;
+ 	    }
+ 	}
      }
  
    if (font_scalable_p (best))
***************
*** 6393,6405 ****
     allocated from the heap and must be freed by the caller, or NULL if
     we can get no information about the font name of C.  It is assured
     that we always get some information for a single byte
!    character.  */
  
  static char *
! choose_face_font (f, attrs, fontset, c)
       struct frame *f;
       Lisp_Object *attrs;
       int fontset, c;
  {
    Lisp_Object pattern;
    char *font_name = NULL;
--- 6421,6438 ----
     allocated from the heap and must be freed by the caller, or NULL if
     we can get no information about the font name of C.  It is assured
     that we always get some information for a single byte
!    character.
! 
!    If NEEDS_OVERSTRIKE is non-zero, a boolean is returned in it to
!    indicate whether the resulting font should be drawn using overstrike
!    to simulate bold-face.  */
  
  static char *
! choose_face_font (f, attrs, fontset, c, needs_overstrike)
       struct frame *f;
       Lisp_Object *attrs;
       int fontset, c;
+      int *needs_overstrike;
  {
    Lisp_Object pattern;
    char *font_name = NULL;
***************
*** 6427,6433 ****
    width_ratio = (SINGLE_BYTE_CHAR_P (c)
  		 ? 1
  		 : CHARSET_WIDTH (CHAR_CHARSET (c)));
!   font_name = best_matching_font (f, attrs, fonts, nfonts, width_ratio);
    return font_name;
  }
  
--- 6460,6467 ----
    width_ratio = (SINGLE_BYTE_CHAR_P (c)
  		 ? 1
  		 : CHARSET_WIDTH (CHAR_CHARSET (c)));
!   font_name = best_matching_font (f, attrs, fonts, nfonts, width_ratio,
! 				  needs_overstrike);
    return font_name;
  }
  
Index: src/xterm.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/xterm.c,v
retrieving revision 1.763
diff -u -r1.763 xterm.c
*** src/xterm.c	14 Nov 2002 14:21:34 -0000	1.763
--- src/xterm.c	16 Nov 2002 15:16:53 -0000
***************
*** 3222,3227 ****
--- 3222,3239 ----
  	    XDrawImageString (s->display, s->window, s->gc, x,
  			      s->ybase - boff, char1b, s->nchars);
  	}
+ 
+       if (s->face->overstrike)
+ 	{
+ 	  /* For overstriking (to simulate bold-face), draw the
+ 	     characters again shifted to the right by one pixel.  */
+ 	  if (s->two_byte_p)
+ 	    XDrawString16 (s->display, s->window, s->gc, x + 1,
+ 			   s->ybase - boff, s->char2b, s->nchars);
+ 	  else
+ 	    XDrawString (s->display, s->window, s->gc, x + 1,
+ 			 s->ybase - boff, char1b, s->nchars);
+ 	}
      }
  }
  
***************
*** 3257,3266 ****
    else
      {
        for (i = 0; i < s->nchars; i++, ++s->gidx)
! 	XDrawString16 (s->display, s->window, s->gc,
! 		       x + s->cmp->offsets[s->gidx * 2],
! 		       s->ybase - s->cmp->offsets[s->gidx * 2 + 1],
! 		       s->char2b + i, 1);
      }
  }
  
--- 3269,3285 ----
    else
      {
        for (i = 0; i < s->nchars; i++, ++s->gidx)
! 	{
! 	  XDrawString16 (s->display, s->window, s->gc,
! 			 x + s->cmp->offsets[s->gidx * 2],
! 			 s->ybase - s->cmp->offsets[s->gidx * 2 + 1],
! 			 s->char2b + i, 1);
! 	  if (s->face->overstrike)
! 	    XDrawString16 (s->display, s->window, s->gc,
! 			   x + s->cmp->offsets[s->gidx * 2] + 1,
! 			   s->ybase - s->cmp->offsets[s->gidx * 2 + 1],
! 			   s->char2b + i, 1);
! 	}
      }
  }
  

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-- 
`There are more things in heaven and earth, Horatio,
 Than are dreamt of in your philosophy.'

Re: overstriking for bold-face

[Werner LEMBERG]

> It makes emacs use `overstriking' (drawing text again shifted by one
> pixel) to simulate bold-face for fonts that have no bold version.
> The same technique is used by programs such as gnome-terminal.

Excellent!  A longer time ago I wanted to implement the same, but due
to lack of time I've never started the project.


    Werner

Re: overstriking for bold-face

[Richard Stallman]

    It makes emacs use `overstriking' (drawing text again shifted by one
    pixel) to simulate bold-face for fonts that have no bold version.  The
    same technique is used by programs such as gnome-terminal.

Presuming the code is correct, this has to be better than completely
failing to support boldness for these fonts.  Thanks for thinking of
it.