bug#50660: 28.0.50; Text artifacting when the cursor moves over text under mouse face that originally displayed a box

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: larsi@gnus.org,  50660@debbugs.gnu.org
> Date: Sat, 16 Oct 2021 08:18:25 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > This part doesn't look right to me: FACE_FOR_CHAR could potentially
> > yield a face with a different font, but the glyph codes in the glyph
> > string will reference the previous font, because
> > get_glyph_face_and_encoding was called before the face was changed.
> 
> But now that I think of it, what if the original font has different
> metrics than the mouse face?  In that case, shouldn't s->font be the
> original font and not the font of the mouse face?  Thanks.

I don't think I follow: what is "the original font" in this context?
And when you say "shouldn't s->font be", do you mean what it should be
before or after the processing in fill_glyph_string?