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: Tue, 21 Sep 2021 15:34:48 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > When the cursor moves, w->phys_cursor.x is recomputed.  AFAIR, in this
> > case we perform the usual redisplay (which updates w->phys_cursor),
> > and then reapply mouse-face, so show_mouse_face should be called
> > again.  But you can easily establish if I'm right by running Emacs in
> > a debugger with a breakpoint in show_mouse_face.  Let me know if you
> > find something unexpected or need help in interpreting the findings.
> 
> Interestingly enough, I don't see show_mouse_face being called when the
> cursor moves within the highlighted area; I only see it called when the
> highlight itself changes, such as when the mouse pointer moves into the
> mouse face.

If show_mouse_face is not called, then there's nothing to be adjusted.
Do you see any display problems with the glyph under the cursor if you
just move the cursor inside the mouse-highlighted region?  If so, can
you show the recipe for reproducing the problem?