bug#26347: patch for mwheel.el

[Tak Kunihiro]

>> Let me take it back and rephrase.  I meant (1) is true for Emacs 24.5
>> on Windows but not for Emacs 25.1 on Windows.  Emacs 25.1 on Windows
>> scrolls horizontally well with auto-hscroll-mode on.
> 
> So I guess this means there is hope your patch could be amended not to
> disable auto-hscroll-mode?

>> Let me take it back and rephrase.  I meant (1) is true for Emacs 24.5
>> on Windows but not for Emacs 25.1 on Windows.  Emacs 25.1 on Windows
>> scrolls horizontally well with auto-hscroll-mode on.
>
> So I guess this means there is hope your patch could be amended not to
> disable auto-hscroll-mode?

Now I leaned auto-hscroll-mode is irrelevant to horizontal scroll.
However, I still insist that it should be off on horizontal and
vertical scrolling.

(A) It should be off during vertical scroll.  Let’s consider a buffer
   is with short and long alternative lines and when point is at the
   end of long line, at the top of current window.  After `scroll-up
   1', point jumps to the end of the next short line and you see scope
   shifts suddenly leftward. This behavior is sometimes unexpected
   one.

(B) It should be off during horizontal scroll.  During horizontal
   scroll, you may scroll a little in vertical direction without
   intention.  The horizontal scroll should be tolerance against such
   perturbation.  The source of concern is same as (A).

The concern (A) is shared with vertical scroll-bar.  With this
respect, the concern should be solved by `scroll-up' not by
`mwheel-scroll'.

I think when point moves off the left edge of the window with cursor
frozen at the left edge of the window, `scroll-up' should scroll up
without horizontal shift.

Conclusion: Yes.