master 608267c 1/2: Support display of non-ASCII characters with aligned columns

[Eli Zaretskii]

branch: master
commit 608267c71e11da9c757c269a5e22e62ef04d0bfe
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Support display of non-ASCII characters with aligned columns
    
    * src/xdisp.c (get_normal_width): New function.
    (gui_produce_glyphs): Use 'get_normal_width' to widen on display
    characters whose width is not an integral multiple of the
    "standard" width.
    (syms_of_xdisp) <align-columns-display>: New boolean variable.
---
 src/xdisp.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/src/xdisp.c b/src/xdisp.c
index 9f93799..fdcf6a6 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -28812,6 +28812,21 @@ normal_char_height (struct font *font, int c)
   return ascent + descent;
 }
 
+/* Return the "standard" pixel width of a character from FACE's font,
+   if the font is fixed-pitch, zero otherwise.  */
+static int
+get_normal_width (struct face *face)
+{
+  struct font *ascii_font = face->ascii_face->font;
+  /* Heuristics: fixed-pitch fonts have the value of MAX-WIDTH not
+     much larger than AVERAGE-WIDTH. */
+  bool fixed_pitch =
+    ascii_font->average_width == ascii_font->space_width
+    && ascii_font->average_width != 0
+    && ascii_font->max_width < 3 * ascii_font->average_width;
+  return fixed_pitch ? ascii_font->space_width : 0;
+}
+
 /* EXPORT for RIF:
    Set *LEFT and *RIGHT to the left and right overhang of GLYPH on
    frame F.  Overhangs of glyphs other than type CHAR_GLYPH are
@@ -30909,6 +30924,17 @@ gui_produce_glyphs (struct it *it)
              it->phys_ascent = pcm->ascent + boff;
              it->phys_descent = pcm->descent - boff;
              it->pixel_width = pcm->width;
+             if (align_columns_display)
+               {
+                 int unit_width = get_normal_width (face);
+                 if (unit_width > 0)
+                   {
+                     int ncolumns =
+                       (it->pixel_width - 1 + unit_width) / unit_width;
+
+                     it->pixel_width = ncolumns * unit_width;
+                   }
+               }
              /* Don't use font-global values for ascent and descent
                 if they result in an exceedingly large line height.  */
              if (it->override_ascent < 0)
@@ -31486,6 +31512,17 @@ gui_produce_glyphs (struct it *it)
        it->glyph_row->contains_overlapping_glyphs_p = true;
 
       it->pixel_width = cmp->pixel_width;
+      if (align_columns_display)
+       {
+         int unit_width = get_normal_width (face);
+         if (unit_width > 0)
+           {
+             int ncolumns =
+               (it->pixel_width - 1 + unit_width) / unit_width;
+
+             it->pixel_width = ncolumns * unit_width;
+           }
+       }
       it->ascent = it->phys_ascent = cmp->ascent;
       it->descent = it->phys_descent = cmp->descent;
       IT_APPLY_FACE_BOX(it, face);
@@ -31531,6 +31568,17 @@ gui_produce_glyphs (struct it *it)
            it->glyph_row->contains_overlapping_glyphs_p = true;
          it->ascent = it->phys_ascent = metrics.ascent;
          it->descent = it->phys_descent = metrics.descent;
+         if (align_columns_display)
+           {
+             int unit_width = get_normal_width (face);
+             if (unit_width > 0)
+               {
+                 int ncolumns =
+                   (it->pixel_width - 1 + unit_width) / unit_width;
+
+                 it->pixel_width = ncolumns * unit_width;
+               }
+           }
        }
       IT_APPLY_FACE_BOX(it, face);
 
@@ -35607,6 +35655,14 @@ variable are ignored and the default 0.25 is used 
instead.  */);
 Value is a number or a cons (WIDTH-DPI . HEIGHT-DPI).  */);
   Vdisplay_pixels_per_inch = make_float (72.0);
 
+  DEFVAR_BOOL ("align-columns-display", align_columns_display,
+    doc: /* Whether to align columns on GUI frames.
+If this is non-nil characters displayed on GUI frames will be
+aligned to produce straight columns.  This is achieved by
+enlarging the pixel width of characters to an integral
+multiple of pixels taken by ASCII characters of the same face.  */);
+    align_columns_display = false;
+
 #ifdef GLYPH_DEBUG
   DEFVAR_INT ("debug-end-pos", debug_end_pos, doc: /* Don't ask.  */);
 #endif