bug#44284: 27.1; with some Unicode font, scrolling upward with the mouse wheel actually scrolls downward when the cursor needs repositioning

[Vincent Lefevre <vincent@vinc17.net>]

On 2020-11-01 20:47:04 +0200, Eli Zaretskii wrote:
> > 3. The fact that row->phys_ascent > row->ascent in compute_line_metrics
> > yields an incorrect behavior. This is about the following comment:
> > 
> >       /* If first line's physical ascent is larger than its logical
> >          ascent, use the physical ascent, and make the row taller.
> >          This makes accented characters fully visible.  */
> 
> This is not a bug, we must keep that code.  It just isn't supposed to
> fire in your case.

For this one, I meant that if the first row is made taller for some
good reason, then this shouldn't yields recentering when scrolling
upward with the mouse wheel, and (move-to-window-line -1) should put
the cursor on the last fully visible display line of the window, as
documented.

Solving (2) would no longer trigger this code in my case, but you
should make sure that this code, which is still useful in some other
cases, behaves correctly with various Emacs features.

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Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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