Re: The unwarranted scrolling assumption

[Lennart Borgman <lennart.borgman@gmail.com>]

On Thu, Jun 17, 2010 at 5:10 AM, Lennart Borgman
<lennart.borgman@gmail.com> wrote:
> On Thu, Jun 17, 2010 at 5:05 AM, Eli Zaretskii <eliz@gnu.org> wrote:
>>> From: Stefan Monnier <monnier@iro.umontreal.ca>
>>> Cc: Lennart Borgman <lennart.borgman@gmail.com>,  storm@cua.dk,  emacs-devel@gnu.org,  david@harpegolden.net
>>> Date: Wed, 16 Jun 2010 20:54:52 -0400
>>>
>>> Indeed what he suggests is probably impossible.  But the end result he's
>>> after is definitely possible: move the window-start as little as possible
>>> (tho still, line by line) to keep point displayed.
>>
>> xdisp.c already tries to do that, we just need to find out why it
>> fails in this particular case.
>
> After trying to restore the clip_changed value when save-restriction,
> widen etc unnecessarily changed I suddenly wonder why they changed it.
> Is not this something that only redisplay should handle? redisplay_can
> easily save the clipping when it sets clip_changed to 0 and compare
> with that when it enters redisplay_window and set clip_changed to 1 if
> the saved clipping does not match.
>
> Does that sound reasonable? (I do not know if I am missing something.)

At least it works. I just tested. First time I am using Emacs without
"jumping scrolling"! :-)

If you think this is the right way to fix it I will send patches later
when I cleaned up a bit.

There is one more similar problem which I do not know how to handle,
in fileio.c. In the function Finsert_file_contents clip_changed is set
to 1. I am not quite sure of the impact of this but it looks wrong to
me to do this. I think the display engine should be told, but it must
decide what to do with redisplay, not fileio.