Re: The unwarranted scrolling assumption

[Eli Zaretskii]

> From: Lennart Borgman <address@hidden>
> Date: Fri, 18 Jun 2010 16:32:07 +0200
> Cc: address@hidden
> 
> On Fri, Jun 18, 2010 at 4:20 PM, Eli Zaretskii <address@hidden> wrote:
> >> From: Lennart Borgman <address@hidden>
> >> Date: Fri, 18 Jun 2010 15:56:38 +0200
> >> Cc: address@hidden, address@hidden, address@hidden
> >>
> >> Can you please explain why window_end_valid flag should be involved?
> >
> > This flag indicates that the redisplay finished and the current glyph
> > matrix is up to date.  It is imperative to know that, because
> > try_scrolling, the function you are trying to get called, reuses
> > portions of the current glyph matrix (to avoid redrawing the entire
> > window).  It is unsafe to reuse the current matrix if it is not
> > guaranteed to be up to date.
> 
> 
> Thanks, that is a clear description.
> 
> But how is that involved here? I save the old clipping in
> reconsider_clip_changes when window_end_valid is non-nil.

You save it when window_end_valid is non-nil, but you use it without
testing window_end_valid.

> Sorry, I was unclear. I meant where it is set to 1. narrow_to_region
> etc set it to 1 and that is not something they should do since they do
> not (and should not) know about the redisplay state.

This flag means that narrowing was changed since the last redisplay.
So yes, setting it in narrow_to_region is the right thing.