Re: The unwarranted scrolling assumption

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: David De La Harpe Golden <david@harpegolden.net>,  emacs-devel@gnu.org
> Date: Thu, 24 Jun 2010 00:18:33 +0200
> 
> > After looking at the code and experimenting a bit, I think there's no
> > other way to prevent recentering on slow machines except set
> > redisplay-dont-pause non-nil.  (You could also try playing with
> > redisplay-preemption-period, which basically gives you more fine
> > granularity than just the ON/OFF you get with redisplay-dont-pause.)
> 
> Could explain the reason why you think it can't be done?

Sorry, my wording was inaccurate and thus misleading.  What I meant to
say was that I see no way of using the try_scrolling optimization
under the conditioned described above, except by setting
redisplay-dont-pause non-nil.  When the window_end_valid flag is nil,
we cannot reuse the current glyph matrix, so we fall back to full
redisplay of the window, and that means displaying point in the middle
of the window.

If avoiding recentering is really important (is it?), I guess we could
try tweaking the full window redisplay code so that it would put point
not in the middle of the window, but rather in the scroll margin.

Is this worth pursuing, and if it is, what values of the various
scroll-* variables should trigger this new behavior?