Re: The unwarranted scrolling assumption

[Eli Zaretskii]

> From: Lennart Borgman <address@hidden>
> Date: Thu, 17 Jun 2010 21:10:55 +0200
> Cc: address@hidden, address@hidden
> 
> > Please show a recipe starting from "emacs -Q".
> 
> I am sorry, I thought that was clear. Just open a large C file for
> example, like window.c. Set the variables as suggested earlier in this
> thread that should prevent "jumping scrolling".
> 
> Then just hold down or rapidly press the down arrow. You will see (if
> your pc is not too fast) that Emacs does the "jumping scrolling" now
> and then. Not every time, but now and then, probably when it gets
> behind in screen updating.

It doesn't jump for me.  And, if the machine is too slow and cannot
keep up with the keyboard's autorepeat rate, then what's wrong with
the "jumps"?  What would you want Emacs to do instead, if it cannot
keep up with the input?

> I said that clip_changed is used only by the display routines. Only
> those routines knows exactly what data was used when redisplay was
> done.
> 
> Clipping is part of the data that might influence redisplay. Changing
> clipping might invalidate what is displayed or it may not.
> 
> In the current code (without my patch) there is a very rough guess
> about this: "if clipping is change we should invalidate the display of
> every window".
> 
> So this is what `narrow-to-region' and `widen' did by setting clip_changed to 
> 1.

But narrow-to-region and widen are not part of the recipe, so how can
they influence scrolling in this case?

> However when I came to think about this I wondered if the display of
> a buffer in several windows is in some (magic) way connected. I
> don't think they are, but anyway I ask you: are they?

It is connected via the buffer-local variables.  I'm not sure this is
what you wanted to hear, but your question is too broad.

Anyway, I don't think it's an efficient way of debugging this -- by
you asking me questions based on some assumptions which I'm not sure
are correct.  Let's stick to trying to understand why scrolling is
rejected by redisplay in favor of recentering (see my other mail).