Re: The unwarranted scrolling assumption

[Lennart Borgman]

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. (Or do I
misread the code there because of the bans I have that forbid me to
read C code corretly?)


>> Can you please also comment on the point where to check if clipping
>> has changed? Is not the entry of redisplay_window the right point for
>> this?
>
> What do you mean by ``where to check if clipping has changed''?  The
> clip_changed flag is checked in many places during redisplay.


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.