bug#51821: 29.0.50; Suggest add variable or frame parameter: line-height

[Eli Zaretskii]

> Date: Tue, 16 Nov 2021 18:45:16 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: tumashu@163.com, 51821@debbugs.gnu.org
> 
> > From: Lars Ingebrigtsen <larsi@gnus.org>
> > Cc: tumashu@163.com,  51821@debbugs.gnu.org
> > Date: Tue, 16 Nov 2021 16:20:52 +0100
> > 
> > > That shouldn't happen, normally.  Emacs selects fonts of the same size
> > > for a face.
> > 
> > No, not really.  Here's a trivial example:
> > 
> > 
> > Note how the lines with jidanni are taller than the rest.
> 
> OK, let me see what can be done about that.

Please try the patch below.  I have a very limited number of cases
with which I can test it, so I think users of CJK scripts should say
what they think.  Basically, set the new variable line-height-factor
to something like 1.2 (more if you enlarge the non-ASCII font to make
double-width characters take close to 2 columns), and see if you get
the desired effect.

If this is what people want, I will install it and document it.

diff --git a/src/window.c b/src/window.c
index e801ff8..a368b6d 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5246,7 +5246,10 @@ grow_mini_window (struct window *w, int delta)
 {
   struct frame *f = XFRAME (w->frame);
   int old_height = window_body_height (w, true);
-  int min_height = FRAME_LINE_HEIGHT (f);
+  int min_height =
+    FLOATP (Vline_height_factor)
+    ? FRAME_LINE_HEIGHT (f) * XFLOAT_DATA (Vline_height_factor)
+    : FRAME_LINE_HEIGHT (f);
 
   eassert (MINI_WINDOW_P (w));
 
@@ -5279,7 +5282,11 @@ grow_mini_window (struct window *w, int delta)
 shrink_mini_window (struct window *w)
 {
   struct frame *f = XFRAME (w->frame);
-  int delta = window_body_height (w, true) - FRAME_LINE_HEIGHT (f);
+  int min_line_height =
+    FLOATP (Vline_height_factor)
+    ? FRAME_LINE_HEIGHT (f) * XFLOAT_DATA (Vline_height_factor)
+    : FRAME_LINE_HEIGHT (f);
+  int delta = window_body_height (w, true) - min_line_height;
 
   eassert (MINI_WINDOW_P (w));
 
diff --git a/src/xdisp.c b/src/xdisp.c
index ef49297..d1f4043 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -22073,6 +22073,18 @@ append_space_for_newline (struct it *it, bool 
default_face_p)
                  it->descent = it->override_descent;
                  boff = it->override_boff;
                }
+             else
+               {
+                 /* Enlarge the ascent to make the row higher by
+                    line-height-factor if needed.  */
+                 if (face == face->ascii_face && it->voffset == 0
+                     && FLOATP (Vline_height_factor))
+                   {
+                     int enlarged_height = ((it->ascent + it->descent)
+                                            * XFLOAT_DATA 
(Vline_height_factor));
+                     it->ascent = enlarged_height - it->descent;
+                   }
+               }
              if (EQ (height, Qt))
                extra_line_spacing = 0;
              else
@@ -30587,9 +30599,9 @@ gui_produce_glyphs (struct it *it)
          /* When no suitable font is found, display this character by
             the method specified in the first extra slot of
             Vglyphless_char_display.  */
-             Lisp_Object acronym = lookup_glyphless_char_display (-1, it);
+         Lisp_Object acronym = lookup_glyphless_char_display (-1, it);
 
-             eassert (it->what == IT_GLYPHLESS);
+         eassert (it->what == IT_GLYPHLESS);
          produce_glyphless_glyph (it, true,
                                   STRINGP (acronym) ? acronym : Qnil);
          goto done;
@@ -30613,6 +30625,15 @@ gui_produce_glyphs (struct it *it)
            {
              it->ascent = FONT_BASE (font) + boff;
              it->descent = FONT_DESCENT (font) - boff;
+             /* If this glyph uses the ASCII face, enlarge the ascent
+                to make the row higher by line-height-factor.  */
+             if (face == face->ascii_face && it->voffset == 0
+                 && FLOATP (Vline_height_factor))
+               {
+                 int enlarged_height = ((it->ascent + it->descent)
+                                        * XFLOAT_DATA (Vline_height_factor));
+                 it->ascent = enlarged_height - it->descent;
+               }
            }
 
          if (get_char_glyph_code (it->char_to_display, font, &char2b))
@@ -30763,6 +30784,13 @@ gui_produce_glyphs (struct it *it)
                {
                  it->ascent = FONT_BASE (font) + boff;
                  it->descent = FONT_DESCENT (font) - boff;
+                 if (face == face->ascii_face && it->voffset == 0
+                     && FLOATP (Vline_height_factor))
+                   {
+                     int enlarged_height = ((it->ascent + it->descent)
+                                            * XFLOAT_DATA 
(Vline_height_factor));
+                     it->ascent = enlarged_height - it->descent;
+                   }
                }
            }
 
@@ -30886,6 +30914,13 @@ gui_produce_glyphs (struct it *it)
                {
                  it->ascent = FONT_BASE (font) + boff;
                  it->descent = FONT_DESCENT (font) - boff;
+                 if (face == face->ascii_face && it->voffset == 0
+                     && FLOATP (Vline_height_factor))
+                   {
+                     int enlarged_height = ((it->ascent + it->descent)
+                                            * XFLOAT_DATA 
(Vline_height_factor));
+                     it->ascent = enlarged_height - it->descent;
+                   }
                }
              it->phys_ascent = it->ascent;
              it->phys_descent = it->descent;
@@ -31243,6 +31278,24 @@ gui_produce_glyphs (struct it *it)
          if (it->glyph_row
              && (metrics.lbearing < 0 || metrics.rbearing > metrics.width))
            it->glyph_row->contains_overlapping_glyphs_p = true;
+         if (it->voffset == 0 && FLOATP (Vline_height_factor))
+           {
+             Lisp_Object font_object = LGSTRING_FONT (gstring);
+             struct font *gstring_font = XFONT_OBJECT (font_object);
+
+             /* This is for when the grapheme cluster displays some
+                ligature using ASCII font: if the height is smaller
+                than line-height-factor says, enlarge the ascent.  */
+             if (face == face->ascii_face
+                 && face->ascii_face->font == gstring_font)
+               {
+                 int enlarged_height =
+                   ((FONT_BASE (gstring_font) + FONT_DESCENT (gstring_font))
+                    * XFLOAT_DATA (Vline_height_factor));
+                 if (metrics.ascent + metrics.descent < enlarged_height)
+                   metrics.ascent = enlarged_height - metrics.descent;
+               }
+           }
          it->ascent = it->phys_ascent = metrics.ascent;
          it->descent = it->phys_descent = metrics.descent;
        }
@@ -35581,6 +35634,16 @@ syms_of_xdisp (void)
 mini-window frame's default font's height.  */);
   Vmax_mini_window_height = make_float (0.25);
 
+  DEFVAR_LISP ("line-height-factor", Vline_height_factor,
+    doc: /* Factor for enlarging the height of lines that use the default font.
+The value should be a float number greater than 1.  It determines how
+much will Emacs enlarge the height of a screen line that shows only
+characters displayed with the default face's font for ASCII characters.
+This is to avoid differences in height between lines that use the
+ASCII font and those which use non-ASCII (for example, Chinese)
+font, which is typically higher than the ASCII one.  */);
+  Vline_height_factor = Qnil;
+
   DEFVAR_LISP ("resize-mini-windows", Vresize_mini_windows,
     doc: /* How to resize mini-windows (the minibuffer and the echo area).
 A value of nil means don't automatically resize mini-windows.