Re: The unwarranted scrolling assumption

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

On Wed, Jun 16, 2010 at 11:22 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Lennart Borgman <lennart.borgman@gmail.com>
>> Date: Wed, 16 Jun 2010 19:35:53 +0200
>> Cc: "Kim F. Storm" <storm@cua.dk>, emacs-devel@gnu.org,
>>       David De La Harpe Golden <david@harpegolden.net>
>>
>> I looked around a bit and it looks like perhaps clip_changed is the
>> problem, but I am not sure. Save-restriction and friends sets this to
>> 1.
>>
>> redisplay_window checks this somewhere around line 14500 where the
>> comment says "Try to scroll by specified few lines". If clip_changed
>> is set then the if arg will be 0 and the "jumping scrolling" will
>> happen. At least that is how I understand it at the moment.
>
> I'm not sure this is the problem.  Can you step through try_scrolling
> in the case that "jumping scrolling" happens, and tell what it does in
> that case and what value it returns?

It is a bit diffucult to step through a problem like this. First you
have to guess what is happening and then you can add a little bit code
that let you just break when it happens for those reasons you guessed
... ;-)

And in this case it does not pass try_scroll when the "jumping
scrolling" happens.

I think the problem is in the handling of clip_changed as I said
before, but I am not sure it can be cured. A lot of calls are made to
narrow_to_region and I thought that the problem was the bugs in the
handling of clip_changed there, but that does not seem to be the whole
story.

But thanks for the tip. Is there anything else that comes up in your head here?