bug#32002: 24.4; Scroll bar start, end not correct

[Stephen Berman]

On Thu, 12 Jul 2018 16:29:50 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>> Date: Thu, 12 Jul 2018 00:11:28 -0700
>> From: Andrew Kurn <kurn@sfu.ca>
>> Cc: 32002@debbugs.gnu.org
>> 
[...]
>> > > Worse, if I mouse the bar up, nothing happens.  The text
>> > > does not reappear.
>> > 
>> > Really?  How do you move the thumb and to what position on the bar?
>> 
>> With the mouse, as I said.  The thumb is now larger than the track,
>> so it doesn't appear to move, but it does, evident when I move it down.
>
> So you are saying that no matter how many time/how long do you move
> the thumb up, the text never re-appears?  Does Emacs receive
> scroll-bar scroll events when you do that (you can verify that with
> "C-h l")?

I see this (on master built with GTK+ Version 3.22.28) when I position
the mouse pointer over the scroll bar and rotate the mouse wheel
(without clicking a mouse button): the scroll bar moves but the text
does not scroll, and view-lossage shows no scroll event.  In contrast,
when I position the mouse pointer over the text area and rotate the
mouse wheel, the text does scroll and view-lossage shows this:
 <down-mouse-5> <mouse-5> ;; mwheel-scroll
 <down-mouse-4> <mouse-4> ;; mwheel-scroll
(FWIW, with Firefox using the same GTK+ and theme, rotating the mouse
wheel over the scroll bar also scrolls the text.)

Also in contrast, when I click and hold down mouse-1 on the scroll bar
and drag it, the scroll bar moves and the text scrolls, and view-lossage
shows this:
 <mouse-1>                ;; scroll-bar-toolkit-scroll

Steve Berman