bug#11860: 24.1; Arabic - Harakat (diacritics, short vowels) don't appear

[Kenichi Handa <handa@gnu.org>]

In article <87bohcty0r.fsf@gnu.org>, Kenichi Handa <handa@gnu.org> writes:

> I'll try to fix Ffont_shape_gstring, and check whether or
> not it breaks rendersing of some scripts.

I've just installed this change.  With this change, I tried
to render several scripts that require CTL (complex text
layout) while setting a breakpoint at this line:
  shaper_error:
    return Qnil;
but, Emacs has never reach that line on GNU/Linux system
(i.e. with m17n-lib and libotf).

---
Kenichi Handa
handa@gnu.org

=== modified file 'src/font.c'
--- src/font.c	2012-09-15 07:06:56 +0000
+++ src/font.c	2012-09-16 11:47:45 +0000
@@ -4295,7 +4295,10 @@
 header of the glyph-string.
 
 If the shaping was successful, the value is GSTRING itself or a newly
-created glyph-string.  Otherwise, the value is nil.  */)
+created glyph-string.  Otherwise, the value is nil.
+
+See the documentation of `composition-get-gstring' for the format of
+GSTRING.  */)
   (Lisp_Object gstring)
 {
   struct font *font;
@@ -4326,44 +4329,45 @@
   if (XINT (n) < LGSTRING_GLYPH_LEN (gstring))
     LGSTRING_SET_GLYPH (gstring, XINT (n), Qnil);
 
+  /* Check FROM_IDX and TO_IDX of each GLYPH in GSTRING to assure that
+     GLYPHS covers all characters in GSTRING.  More formally, provided
+     that NCHARS is the number of characters in GSTRING, N is the
+     number of glyphs, and GLYPHS[i] is the ith glyph, FROM_IDX and
+     TO_IDX of each glyph must satisfy these conditions:
+
+       GLYPHS[0].FROM_IDX == 0
+       GLYPHS[i].FROM_IDX <= GLYPHS[i].TO_IDX
+       if (GLYPHS[i].FROM_IDX == GLYPHS[i-1].FROM_IDX)
+         ;; GLYPHS[i] and GLYPHS[i-1] belongs to the same grapheme cluster
+         GLYPHS[i].TO_IDX == GLYPHS[i-1].TO_IDX
+       else
+         ;; Be sure to cover all characters.
+         GLYPHS[i].FROM_IDX == GLYPHS[i-1].TO_IDX + 1
+       GLYPHS[N-1].TO_IDX == NCHARS - 1 */
   glyph = LGSTRING_GLYPH (gstring, 0);
   from = LGLYPH_FROM (glyph);
   to = LGLYPH_TO (glyph);
-  for (i = 1, j = 0; i < LGSTRING_GLYPH_LEN (gstring); i++)
+  if (from != 0 || to < from)
+    goto shaper_error;
+  for (i = 1; i < LGSTRING_GLYPH_LEN (gstring); i++)
     {
-      Lisp_Object this = LGSTRING_GLYPH (gstring, i);
-
-      if (NILP (this))
+      glyph = LGSTRING_GLYPH (gstring, i);
+      if (NILP (glyph))
 	break;
-      if (NILP (LGLYPH_ADJUSTMENT (this)))
-	{
-	  if (j < i - 1)
-	    for (; j < i; j++)
-	      {
-		glyph = LGSTRING_GLYPH (gstring, j);
-		LGLYPH_SET_FROM (glyph, from);
-		LGLYPH_SET_TO (glyph, to);
-	      }
-	  from = LGLYPH_FROM (this);
-	  to = LGLYPH_TO (this);
-	  j = i;
-	}
-      else
-	{
-	  if (from > LGLYPH_FROM (this))
-	    from = LGLYPH_FROM (this);
-	  if (to < LGLYPH_TO (this))
-	    to = LGLYPH_TO (this);
-	}
+      if (! (LGLYPH_FROM (glyph) <= LGLYPH_TO (glyph)
+	     && (LGLYPH_FROM (glyph) == from
+		 ? LGLYPH_TO (glyph) == to
+		 : LGLYPH_FROM (glyph) == to + 1)))
+	goto shaper_error;
+      from = LGLYPH_FROM (glyph);
+      to = LGLYPH_TO (glyph);
     }
-  if (j < i - 1)
-    for (; j < i; j++)
-      {
-	glyph = LGSTRING_GLYPH (gstring, j);
-	LGLYPH_SET_FROM (glyph, from);
-	LGLYPH_SET_TO (glyph, to);
-      }
+  if (to != LGSTRING_CHAR_LEN (gstring) - 1)
+    goto shaper_error;
   return composition_gstring_put_cache (gstring, XINT (n));
+
+ shaper_error:
+  return Qnil;
 }
 
 DEFUN ("font-variation-glyphs", Ffont_variation_glyphs, Sfont_variation_glyphs,