bug#54646: 29.0.50; set-fontset-font and font clipping issues

[Visuwesh <visuweshm@gmail.com>]

[Sunday April 03, 2022] Eli Zaretskii wrote:

>> From: Visuwesh <visuweshm@gmail.com>
>> Cc: rpluim@gmail.com,  54646@debbugs.gnu.org
>> Date: Sun, 03 Apr 2022 15:56:35 +0530
>> 
>> > The %c format is only good for single-byte characters, which these
>> > ones aren't.  Please use %x to print them (in hex).
>> >
>> 
>> Will do, thanks.
>> 
>> > Also, I think printing everything is too much, and doesn't allow to
>> > focus.  Please print only when the character's code is one of those
>> > involved in the problematic display.
>> 
>> Unfortunately, the characters that are problematic tend to differ from
>> each run.  Nevertheless, I will hand-pick the problematic characters and
>> send it.
>
> That'd be good.  We need a reproducible case to work with.
>
>> >   if (chars[char_idx] == CHAR1
>> >       || chars[char_idx] == CHAR2
>> >       || chars[char_idx] == CHAR3)
>> >     printf (...
>> >
>> > where CHAR1, CHAR2, and CHAR3 are the characters involved in the
>> > problematic display, according to "C-u C-x =".
>> >
>> > May I suggest that you show me the code you add to hbfont.c before you
>> > run it?  This would avoid unnecessary iterations for you.
>> >
>> 
>> Sure,
>
> This is okay, but please don't forget to add that 'if' condition.  I
> think the characters involved in the composition, and in addition one
> character on each side of those, should be enough.

It seems like I did not get my point across: the characters that tend
to be rendered problematic differ from each run so I will hand-pick the
data for the problematic characters in _that_ run and send it.

>
> Please show the final code, so that I could then interpret the
> print-outs correctly.
>
> Thanks.

Considering the above, it would be

diff --git a/src/hbfont.c b/src/hbfont.c
index 2721a66120..9351359558 100644
--- a/src/hbfont.c
+++ b/src/hbfont.c
@@ -490,6 +490,7 @@ hbfont_shape (Lisp_Object lgstring, Lisp_Object direction)
     : NULL;
   if (!hb_font)
     return make_fixnum (0);
+  printf("position_unit begin_hb_font: %f\n", position_unit);
 
   hb_bool_t success = hb_shape_full (hb_font, hb_buffer, NULL, 0, NULL);
   if (font->driver->end_hb_font)
@@ -589,10 +590,17 @@ hbfont_shape (Lisp_Object lgstring, Lisp_Object direction)
       LGLYPH_SET_RBEARING (lglyph, metrics.rbearing);
       LGLYPH_SET_ASCENT (lglyph, metrics.ascent);
       LGLYPH_SET_DESCENT (lglyph, metrics.descent);
+      printf("lbearing %d rbearing %d width %d ascent %d descent %d\n",
+	     metrics.lbearing, metrics.rbearing, metrics.width, metrics.ascent, metrics.descent);
 
       xoff = lround (pos[i].x_offset * position_unit);
       yoff = - lround (pos[i].y_offset * position_unit);
       wadjust = lround (pos[i].x_advance * position_unit);
+      printf("%x %x %x xadvance %d yadvance %d xoffset %d yoffset %d\n",
+	     (chars_idx == 0 ? 1 : chars[char_idx-1]), chars[char_idx],
+	     (chars_idx == glyph_len-1 ? 1 : chars[char_idx+1]),
+	     pos[i].x_advance, pos[i].y_advance, pos[i].x_offset, pos[i].y_offset);
+      printf("xpos %d yoff %d wadjust %d\n", xoff, yoff, wadjust);
       if (xoff || yoff || wadjust != metrics.width)
 	LGLYPH_SET_ADJUSTMENT (lglyph, CALLN (Fvector,
 					      make_fixnum (xoff),