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

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

> I don't understand: if the mouse-face changes the font, you want to
> ignore that? why does that make sense?
>
> And mouse-face is defined for ASCII font only anyway, which is why the
> code calls FACE_FOR_CHAR.  You want to ignore the font that this call
> produces?

Yes, precisely.

> A face includes the font, so I don't understand why you want to
> separate them, and how.
>
> As for the old code: are you sure that's not a bug, part of the same
> subtle issue you are trying to fix?

I'm reasonably sure.  Under the old code in *term, moving the mouse over
the entry for `glyphless-char' in list-faces-display results in nothing,
while under the new code (where s->font == s->face->font even under
mouse face) the section under mouse face overlaps with its surroundings
and is otherwise glitchy, because the mouse face's font is larger than
the original face's font.