bug#50798: 28.0.50; Tab line close button is off-center until it is highlighted with the mouse

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: larsi@gnus.org,  luangruo@yahoo.com,  50798@debbugs.gnu.org
> Date: Mon, 04 Oct 2021 20:41:09 +0300
> 
> >> It solves the problem because tab-line-close-highlight doesn't inherit
> >> from other faces.  It's face inheritance that caused the problem
> >> with vertical movement of the button.
> >
> > I'd still like to understand why this happens.  It sounds like a bug.
> >
> > You said you found some coordinates miscalculated, but didn't provide
> > any details.  Could you please provide those details, so I could try
> > to look at that?  Debugging this is notoriously hard, because the code
> > is entered upon almost every mouse movement, so it is important for me
> > to know which code I'm investigating to be able to set up the
> > breakpoint conditions that avoid triggering at non-interesting
> > moments.
> 
> I don't understand how coordinates are calculated,
> so I'll try to create a minimal test case for debugging.

Thanks.