Re: The unwarranted scrolling assumption

[Lennart Borgman]

On Wed, Jun 16, 2010 at 11:36 AM, Kim F. Storm <address@hidden> wrote:
> Lennart Borgman <address@hidden> writes:
>
>> But this is over the head for me.
>>
>> Kim, are you there? Help!
>>
>
> I'm here, but I think at this time it is way over my head too.
>
> Unless you work on xdisp almost every day, you wont know what's up or down
> and it's been two years since I last looked.


I see. Perhaps you can comment on my thoughts below.

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.

The comment for clip_changed says

  /* Set nonzero whenever the narrowing is changed in this buffer.  */
  int clip_changed;

This does not really tell what it is used for. Is it used for the
display engine or something else (or several things)?

If it is meant for the display engine only then I think that
save-restriction and friends should be a bit more careful with setting
it since there is no need to set it unless the widening state has
changed when next redisplay is done.