Re: A patch for enforcing double-width CJK character display

[黄建忠 <jianzhong.huang@i-soft.com.cn>]

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Hi, Eli,

Many many thinks, your suggestion is really very very great.
Now we can get the frame font width no matter it is default, remapped or 
rescaled.

I updated the patch as you suggested, other changes also include in 
attachment:
1, remove "default_font_width" global variable, get font width from 
FRAME_PTR as you sugguested.
2, pass FRAME_PTR to every xftfont_info structure, we can use it anywhere.
3, add a feild "is_cjk" to "xftfont_info" structure, initialize it when 
xftfont_open, avoid call "is_cjk_font" many times when draw and extents 
calculation.

Now, it works very well with font remapping, rescaling.



于 2012年04月12日 22:27, Eli Zaretskii 写道:
>> Date: Thu, 12 Apr 2012 19:18:39 +0800
>> From: 黄建忠<jianzhong.huang@i-soft.com.cn>
>> CC: kanru@kanru.info, emacs-devel@gnu.org
>>
>>>> Can anybody provide a clue how to catch the new width of default font
>>>> via FRAME_PTR when scale happened?
>>> I don't think there is a way to do that, if all you have is the frame
>>> pointer.  text-scale-mode does not modify the frame's default font, it
>>> remaps the 'default' face to another face which specifies a larger or
>>> a smaller font.  So the way to find the width of the font after
>>> scaling is to get hold of the font itself, or of the face to which
>>> 'default' was remapped.  Then you can use FONT_WIDTH, I think (but I
>>> didn't test this).
>> I can get the default font(the first font loaded when frame be
>> initialized) via FRAME_FONT, it's great that it can not be changed after
>> first font loaded.
>> But I still can not get the current width after scale, since the props
>> of FRAME_FONT also not be changed.
>> [...]
>> I noticed there were some global Lisp_Object such as
>> "f_Vface_font_rescale_alist"/"f_Vface_remapping_alist"/"f_Vface_new_frame_defaults",
>> maybe I can use them, Hope so.
> This will retrieve the numerical ID of the default face on frame F:
>
>    int id = lookup_basic_face (F, DEFAULT_FACE_ID);
>
> lookup_basic_face consults f_Vface_remapping_alist.  If the value of
> id above is different from DEFAULT_FACE_ID, that means the default
> face was remapped.  Then you can get the remapped face like this:
>
>    struct face *face = FACE_FROM_ID (F, id);
>
> Now the font of the face is available as
>
>    struct font *font = face->font;
>
> And I think FONT_WIDTH (font) will give you the width you want to use
> instead of FRAME_COLUMN_WIDTH.
>
> Again, this is 100% untested.  Good luck!
>
>

[-- Attachment #2: emacs-cjk-monospace-v8.patch --]
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--- emacs-24.1.50/src/xftfont.c	2012-04-13 00:47:16.703598929 +0800
+++ emacs-24.1.50.cjk/src/xftfont.c	2012-04-13 00:50:02.909608551 +0800
@@ -61,6 +61,8 @@
   Display *display;
   int screen;
   XftFont *xftfont;
+  FRAME_PTR frame; /* hold frame ptr, cjk double width fix need it */
+  int is_cjk; /* Flag to tell if it is CJK font or not. */
 };
 
 /* Structure pointed by (struct face *)->extra  */
@@ -137,6 +139,62 @@
 }
 
 
+static int is_cjk_font(struct xftfont_info *);
+static int calc_cjk_padding(int, int);
+static int frame_default_font_width(FRAME_PTR);
+
+/* Check whether the font contains CJK Ideograph 'number one', 0x4E00,
+   It should be ok for Chinese/Japanese font.
+   Or font contains Korean script syllable 'Ka',0xAC00,
+   because Korean fonts may not have any Chinese characters at all.
+   codes from xterm.*/
+static int
+is_cjk_font(struct xftfont_info *xftfont_info)
+{
+  if(XftCharExists(xftfont_info->display, xftfont_info->xftfont, 0x4E00) ||
+      XftCharExists(xftfont_info->display, xftfont_info->xftfont, 0xAC00))
+    return 1;
+  return 0; 
+}
+
+/* Caculate the padding according to default font width */
+static int
+calc_cjk_padding(int default_font_width, int char_width)
+{
+  int padding = 0;
+  if( default_font_width == 0 || /* default font is not monospace */
+      char_width < default_font_width || /* almost impossible */
+      char_width == default_font_width) /* already good */
+    return 0;
+  /* get the padding, all cjk symbols is DOUBLE width */
+  padding = default_font_width * 2 - char_width;
+  /* 1, Some old CJK pcf fonts may bigger than 2*default_font_width.
+     2, User may set a very big font size for script HAN manually.
+     Keep it unchanged, NOT adjust default font width. */
+  return padding > 0 ? padding : 0;                   
+}
+
+/* 
+   Get the width of default font from FRAME_PTR.
+   If it is monospace font, return the space_width(as same as font width)
+   else return 0.
+   font remap can be supported now.
+   Thanks to Eli. */
+static int 
+frame_default_font_width(FRAME_PTR f)
+{
+  int id = lookup_basic_face (f, DEFAULT_FACE_ID);
+  struct face *face = FACE_FROM_ID (f, id);
+  if(face && face->font) {
+    Lisp_Object font_object;
+    XSETFONT (font_object, face->font);
+    if(XINT(AREF (font_object, FONT_SPACING_INDEX)) != FONT_SPACING_MONO)
+      return 0;
+    return face->font->space_width; 
+  }
+  return 0;
+}
+
 static Lisp_Object xftfont_list (Lisp_Object, Lisp_Object);
 static Lisp_Object xftfont_match (Lisp_Object, Lisp_Object);
 static Lisp_Object xftfont_open (FRAME_PTR, Lisp_Object, int);
@@ -434,6 +492,14 @@
       XftTextExtents8 (display, xftfont, ascii_printable + 1, 94, &extents);
       font->average_width = (font->space_width + extents.xOff) / 95;
     }
+
+  /* to fix CJK double width alignment issue.
+     pass FRAME_PTR to every xftfont_info structure,
+     we can not get it in "xftfont_text_extents". */
+  xftfont_info->frame = f;
+  /* mark it is CJK font or not when font opened,
+     avoid calling "is_cjk_font" many times. */
+  xftfont_info->is_cjk = is_cjk_font(xftfont_info);
   UNBLOCK_INPUT;
 
   font->ascent = xftfont->ascent;
@@ -593,20 +659,27 @@
 {
   struct xftfont_info *xftfont_info = (struct xftfont_info *) font;
   XGlyphInfo extents;
-
+  int cjk_padding = 0;
+  int l_padding = 0;
+  int r_padding = 0;
   BLOCK_INPUT;
   XftGlyphExtents (xftfont_info->display, xftfont_info->xftfont, code, nglyphs,
 		   &extents);
+  if(xftfont_info->is_cjk)
+    cjk_padding = calc_cjk_padding(frame_default_font_width(xftfont_info->frame), extents.xOff);
+  /* cjk_padding may equals to 0, then all is zero, still ok */
+  l_padding = cjk_padding >> 1; /* get half */
+  r_padding = cjk_padding - l_padding; /* may not divided by 2 exactly */ 
   UNBLOCK_INPUT;
   if (metrics)
     {
-      metrics->lbearing = - extents.x;
-      metrics->rbearing = - extents.x + extents.width;
-      metrics->width = extents.xOff;
+      metrics->lbearing = - extents.x - l_padding;
+      metrics->rbearing = - extents.x + extents.width + r_padding;
+      metrics->width = extents.xOff + cjk_padding;
       metrics->ascent = extents.y;
       metrics->descent = extents.height - extents.y;
     }
-  return extents.xOff;
+  return extents.xOff + cjk_padding;
 }
 
 static XftDraw *
@@ -664,9 +737,28 @@
     for (i = 0; i < len; i++)
       XftDrawGlyphs (xft_draw, &fg, xftfont_info->xftfont,
 		     x + i, y, code + i, 1);
-  else
-    XftDrawGlyphs (xft_draw, &fg, xftfont_info->xftfont,
-		   x, y, code, len);
+  else {
+      if(!xftfont_info->is_cjk)
+        XftDrawGlyphs (xft_draw, &fg, xftfont_info->xftfont, x, y, code, len);
+      else { 
+         /* draw CJK glyphs one by one and adjust the offset */
+         int default_font_width = frame_default_font_width(xftfont_info->frame);
+         for (i = 0; i < len; i++) {
+           int cjk_padding = 0;
+           int offset = 0;
+           XGlyphInfo extents;
+           XftGlyphExtents (xftfont_info->display, xftfont_info->xftfont, code+i, 1,
+                            &extents);
+           cjk_padding = calc_cjk_padding(default_font_width,extents.xOff);
+           if(cjk_padding)
+             offset = default_font_width * i * 2 + (cjk_padding>>1);
+           else 
+             offset = extents.xOff * i; 
+           XftDrawGlyphs (xft_draw, &fg, xftfont_info->xftfont,
+                            x+offset, y, code+i, 1);
+         }
+      }
+  }
   UNBLOCK_INPUT;
 
   return len;