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

[Eli Zaretskii]

> From: Visuwesh <visuweshm@gmail.com>
> Cc: rpluim@gmail.com,  54646@debbugs.gnu.org
> Date: Fri, 22 Apr 2022 16:16:07 +0530
> 
> >> and the GOOD case for bb9 bbf is
> >> 
> >>     lbearing 1 rbearing 28 width 28 ascent 9 descent 5
> >>     1 bb9 bbf xadvance 1809 yadvance 0 xoffset 0 yoffset 0
> >>     xpos 0 yoff 0 wadjust 28
> >> 
> >> and the BAD case is
> >> 
> >>     lbearing 1 rbearing 28 width 28 ascent 9 descent 5
> >>     1 bb9 bbf xadvance 3193 yadvance 0 xoffset 0 yoffset 0
> >>     xpos 0 yoff 0 wadjust 50
> >
> > This looks like HarfBuzz is feeding us incorrect data for some reason,
> > but I cannot imagine what that reason could be, sorry.
> 
> Could it be some kind of cache?  Because when Emacs rendered the entire
> webpage, I was unable to reproduce the issue.

When Emacs have rendered the entire page, we no longer call HarfBuzz,
because the composition data is indeed cached by Emacs.

The print-outs you produced are from calling HarfBuzz, so our caching
cannot affect that, AFAIU.