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

[martin rudalics <rudalics@gmx.at>]

 >> Maybe Mike's theme doesn't show the arrow keys or the mouse position
 >> gets interpreted wrongly.
 >
 > I'm not sure what you mean by "arrow keys".  Is this the same thing as
 > the "stepper buttons" I've been referring to?

Yes.  I'll call them stepper buttons from now on.

 >> At least his "right-click in the scrollbar
 >> above or below the thumb (slider)" is a misinterpretation of how
 >> scroll bars are supposed to behave.  Such clicks should be interpreted
 >> as "jumps" as I tried to explain elsewhere.
 >
 > https://developer.gnome.org/gtk3/stable/GtkScrollbar.html is the closest
 > I've found to documentation on how a (GTK3) scrollbar is supposed to
 > behave.  I do not see that it says what should happen if the user
 > right-clicks.  So I am not convinced that I have misinterpreted
 > anything.  I did test my right-click idea on gedit before posting it,
 > and a single right-click in the scroll area behaved the same as
 > left-clicking on the corresponding stepper button.
 >
 > I have found some discussion at
 > https://bugzilla.redhat.com/show_bug.cgi?id=1495520, which suggests that
 > right-click is intended for smooth scrolling--at least in some versions
 > of GTK3.  And I see that right-click-and-hold does produce smooth
 > scrolling on gedit, though I'm unable to get the variable-speed effect
 > mentioned at https://bugzilla.redhat.com/show_bug.cgi?id=1495520#c9.
 >
 > Could it make a difference that I've been using MATE and Cinnamon for
 > testing?

We first have to make sure that you indeed click on the stepper
buttons.  For this purpose please do the following with Emacs -Q:
Evaluate

M-: (setq window-min-height 1) RET
C-x 2
M-: (window-resize nil (- 2 (window-height))) RET

This should get you a one-line window on top of the frame.  Here this
window has just two small stepper buttons and no slider.  Hopefully,
yours is the same.  I wonder what scroll bars without stepper buttons
show in such a case.

Now please tell us what clicking or pressing such a button produces.
If running this under GDB reveals that in xg_scroll_callback 'scroll'
equals GTK_SCROLL_JUMP, then please tell us the values of 'whole' and
'value' in that case.

Thank you, martin