bug#29002: it.first_visible_x is erroneously 0 while horizontal scrolling.

[Eli Zaretskii]

> Date:  Sun, 29 Oct 2017 11:56:22 -0700
> From:  Keith David Bershatsky <esq@lawlist.com>
> Cc:  29002@debbugs.gnu.org
> 
> I agree ... and that leads us to bug #29002.  :)
> 
> In the normal situation, the screen refreshes when the arrow key is used and 
> non-current lines cease to be horizontally scrolled.  In the current example, 
> however, non-current lines remain horizontally scrolled and Emacs "thinks" 
> that they are not.  When I say that Emacs "thinks" they are not, I am 
> referring to IT.

What Emacs "thinks" is on display.  And there we see hscrolled lines.
So first_visible_x must be non-zero, and that is what I see.  If
first_visible_x were zero, you'd see the line's text starting with the
first character of each line.  I very much doubt that this is somehow
Windows-specific, since xdisp.c is the platform-independent part of
the display engine.

Or maybe the horizontal scroll bar on macOS somehow causes this.  What
happens if you scroll-right with some key, like F8, and not with the
mouse?

(In any case, invoking scroll-right in this situation makes very
little sense to me.)