bug#24582: 25.1; liga incorrect work (dublicate)

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

>>>>> On Wed, 05 Oct 2016 14:15:34 +0300, eli@fastmail.com said:

> Please see the attached screenshot.
>> So the problem is text alignment due to display of characters such
>> as ⇒, is that right?
> Yes

I could reproduce it with Hasklig 11pt.  Does the following patch work
for you?

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp

diff --git a/src/macfont.m b/src/macfont.m
index 16e489d..eb7dcd9 100644
--- a/src/macfont.m
+++ b/src/macfont.m
@@ -1123,7 +1123,10 @@ struct macfont_metrics
      glyph width.  The `width_int' member is an integer that is
      closest to the width.  The `width_frac' member is the fractional
      adjustment representing a value in [-.5, .5], multiplied by
-     WIDTH_FRAC_SCALE.  For synthetic monospace fonts, they represent
+     WIDTH_FRAC_SCALE.  For monospace fonts, non-zero `width_frac'
+     means `width_int' is further adjusted to a multiple of the
+     (rounded) font width, and `width_frac' represents adjustment per
+     unit character.  For synthetic monospace fonts, they represent
      the advance delta for centering instead of the glyph width.  */
   signed width_frac : WIDTH_FRAC_BITS, width_int : 16 - WIDTH_FRAC_BITS;
 };
@@ -1150,6 +1153,27 @@ enum metrics_status
 #define LCD_FONT_SMOOTHING_LEFT_MARGIN	(0.396f)
 #define LCD_FONT_SMOOTHING_RIGHT_MARGIN	(0.396f)
 
+/* If FONT is monospace and WIDTH can be regarded as a multiple of its
+   width where the multiplier is greater than 1, then return the
+   multiplier.  Otherwise return 0.  */
+static int
+macfont_monospace_width_multiplier (struct font *font, CGFloat width)
+{
+  struct macfont_info *macfont_info = (struct macfont_info *) font;
+  int multiplier = 0;
+
+  if (macfont_info->spacing == MACFONT_SPACING_MONO
+      && font->space_width != 0)
+    {
+      multiplier = lround (width / font->space_width);
+      if (multiplier == 1
+	  || lround (width / multiplier) != font->space_width)
+	multiplier = 0;
+    }
+
+  return multiplier;
+}
+
 static int
 macfont_glyph_extents (struct font *font, CGGlyph glyph,
                        struct font_metrics *metrics, CGFloat *advance_delta,
@@ -1194,13 +1218,38 @@ macfont_glyph_extents (struct font *font, CGGlyph glyph,
       else
         fwidth = mac_font_get_advance_width_for_glyph (macfont, glyph);
 
-      /* For synthetic mono fonts, cache->width_{int,frac} holds the
-         advance delta value.  */
-      if (macfont_info->spacing == MACFONT_SPACING_SYNTHETIC_MONO)
-        fwidth = (font->pixel_size - fwidth) / 2;
-      cache->width_int = lround (fwidth);
-      cache->width_frac = lround ((fwidth - cache->width_int)
-                                  * WIDTH_FRAC_SCALE);
+      if (macfont_info->spacing == MACFONT_SPACING_MONO)
+	{
+	  /* Some monospace fonts for programming languages contain
+	     wider ligature glyphs consisting of multiple characters.
+	     For such glyphs, simply rounding the combined fractional
+	     width to an integer can result in a value that is not a
+	     multiple of the (rounded) font width.  */
+	  int multiplier = macfont_monospace_width_multiplier (font, fwidth);
+
+	  if (multiplier)
+	    {
+	      cache->width_int = font->space_width * multiplier;
+	      cache->width_frac = lround ((fwidth / multiplier
+					   - font->space_width)
+					  * WIDTH_FRAC_SCALE);
+	    }
+	  else
+	    {
+	      cache->width_int = lround (fwidth);
+	      cache->width_frac = 0;
+	    }
+	}
+      else
+	{
+	  /* For synthetic mono fonts, cache->width_{int,frac} holds
+	     the advance delta value.  */
+	  if (macfont_info->spacing == MACFONT_SPACING_SYNTHETIC_MONO)
+	    fwidth = (font->pixel_size - fwidth) / 2;
+	  cache->width_int = lround (fwidth);
+	  cache->width_frac = lround ((fwidth - cache->width_int)
+				      * WIDTH_FRAC_SCALE);
+	}
       METRICS_SET_STATUS (cache, METRICS_WIDTH_VALID);
     }
   if (macfont_info->spacing == MACFONT_SPACING_SYNTHETIC_MONO)
@@ -1237,6 +1286,10 @@ macfont_glyph_extents (struct font *font, CGGlyph glyph,
                                     / (CGFloat) (WIDTH_FRAC_SCALE * 2));
               break;
             case MACFONT_SPACING_MONO:
+	      if (cache->width_frac)
+		bounds.origin.x += - ((cache->width_frac
+				       / (CGFloat) (WIDTH_FRAC_SCALE * 2))
+				      * (cache->width_int / font->space_width));
               break;
             case MACFONT_SPACING_SYNTHETIC_MONO:
               bounds.origin.x += (cache->width_int
@@ -1273,7 +1326,16 @@ macfont_glyph_extents (struct font *font, CGGlyph glyph,
                                  / (CGFloat) (WIDTH_FRAC_SCALE * 2)));
           break;
         case MACFONT_SPACING_MONO:
-          *advance_delta = 0;
+	  if (cache->width_frac)
+	    *advance_delta = 0;
+	  else
+	    {
+	      CGFloat delta = - ((cache->width_frac
+				  / (CGFloat) (WIDTH_FRAC_SCALE * 2))
+				 * (cache->width_int / font->space_width));
+
+	      *advance_delta = (force_integral_p ? round (delta) : delta);
+	    }
           break;
         case MACFONT_SPACING_SYNTHETIC_MONO:
           *advance_delta = (force_integral_p ? cache->width_int
@@ -3139,7 +3201,7 @@ macfont_shape (Lisp_Object lgstring)
       struct mac_glyph_layout *gl = glyph_layouts + i;
       EMACS_INT from, to;
       struct font_metrics metrics;
-      int xoff, yoff, wadjust;
+      int xoff, yoff, wadjust, multiplier;
 
       if (NILP (lglyph))
         {
@@ -3192,7 +3254,11 @@ macfont_shape (Lisp_Object lgstring)
 
       xoff = lround (gl->advance_delta);
       yoff = lround (- gl->baseline_delta);
-      wadjust = lround (gl->advance);
+      multiplier = macfont_monospace_width_multiplier (font, gl->advance);
+      if (multiplier)
+	wadjust = font->space_width * multiplier;
+      else
+	wadjust = lround (gl->advance);
       if (xoff != 0 || yoff != 0 || wadjust != metrics.width)
         {
           Lisp_Object vec;