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

[Mike Kupfer]

Eli Zaretskii 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?

I can duplicate the behavior that Andrew reported, but only with

  (setq scroll-bar-adjust-thumb-portion nil)

and only if the entire buffer is displayed in the window.

With

  (setq scroll-bar-adjust-thumb-portion t)

if I

  a. drag the thumb until it touches the bottom of the track
  b. continue moving the mouse to the bottom of the thumb (holding button1)
  c. change direction and start moving the mouse up (holding button1)

the thumb doesn't move until the mouse has traveled up a bit (which
makes sense).  And the text that had scrolled off the top of the window
doesn't reappear until the thumb starts to move (which also makes
sense).

With

  (setq scroll-bar-adjust-thumb-portion nil)

the thumb takes up the entire track.  (I'm doing this testing with a
theme that lacks steppers.)  Moving the mouse down (while holding
button1) does not move the thumb, but it does cause the text to scroll
up.  Moving the mouse up (while holding button1) does not cause the text
to reappear, even if I move the mouse all the way to the top of the
thumb.

> Does Emacs receive
> scroll-bar scroll events when you do that (you can verify that with
> "C-h l")?

Yes (at least for my test scenario).

best regards,
mike