bug#70386: 30.0.50; (recenter 0 t) does not put point on top of the window

[Eli Zaretskii <eliz@gnu.org>]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: luangruo@yahoo.com, 70386@debbugs.gnu.org
> Date: Mon, 15 Apr 2024 18:45:48 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> In other words, the window slowly scrolls up, moving the point to the
> >> top, but then quickly resets back to how it looked like before the
> >> scroll started.
> >
> > No, it does not, at least not on my system.  There's a small vscroll
> > (you should see it if you move the cursor vertically with C-p after
> > eval-buffer returns).  So the code works, it just yields a vscroll
> > that is not what you expect for some reason (and in about 50% of my
> > attempts -- in the rest the code works as you expect).
> 
> See the attached screencast on what I am seeing.

If you look closely, you will see that even in that screencast the
starting and the ending display are not identical: there's a small
vertical displacement in the latter wrt the former.

Besides, the start of the screencast is not immediately after entering
"emacs -Q".  I think you started recording after several attempts, and
didn't restore the initial position after each attempt.  I know this
because the first line of *scratch* is barely visible when you begin
the screencast.