Re: Redisplay resets vscroll when window start changes

[Michael Welsh Duggan]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Po Lu <luangruo@yahoo.com>
>> Cc: emacs-devel@gnu.org
>> Date: Tue, 16 Nov 2021 21:38:57 +0800
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> > If you are moving to another line, how would it make sense to leave
>> > vscroll alone?  Or what am I missing?
>> 
>> Basically, if someone has the following content in a window:
>> 
>> AAAA
>> BBBB
>> CCCC
>> DDDD
>> EEEE
>> FFFF
>> GGGG
>> HHHH
>> 
>> And point is on the first "G", while vscroll is set so that part of
>> "AAAA" is obscured, he will expect moving up so that point is on the
>> first "F" to not reset the vscroll.
>
> Moving up pixelwise? that should gradually show more and more of AAAA
> with each pixel movement.  How is vscroll involved here?
>
> Or are you talking about some other kind of "moving up?

Given the following buffer:

Screenshot from 2021-11-16 12-06-46.png
Description: PNG image

If I type `C-x C-e` at point, I get this:

Screenshot from 2021-11-16 12-07-41.png
Description: PNG image

At this point, if I type, say, `C-n', I get this:

Screenshot from 2021-11-16 12-08-51.png
Description: PNG image

As you can see, the vscroll has reset, despite simply doing
cursor-movement within the visible reason.  This is the behavior that I
believe Po Lu is complaining about.  Why should cursor movement that
wouldn't cause a scrolling event under normal circumstances cause one
when vertical fractional scrolling is present?

-- 
Michael Welsh Duggan
(md5i@md5i.com)