Re: The unwarranted scrolling assumption

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: emacs-devel@gnu.org
> Date: Fri, 18 Jun 2010 14:30:11 -0400
> 
> > According to my reading, it stops the search for point if it is more
> > than 10 lines below (resp above) the scroll margin.  The reason is
> > speed, as the comment says.  Can we safely assume that whoever sets
> > scroll-conservatively to the maximum value gives up this speed
> > consideration?
> 
> I think so, yes.

OK.  I installed a change along these lines (revno 100619).  It
actually goes a tad farther, in that it computes the limit for
searching for point from the values of scroll-conservatively and
scroll-step, even when scroll-conservatively is less than
most-positive-fixnum, instead of using an arbitrary limit of 10 screen
lines.

Would people who customize these variables (and those who use
scroll-*-aggressively) please see if the new behavior is to their
liking?

Btw, the limit of 10 screen lines comes from this change:

  2008-10-27  Chong Yidong  <cyd@stupidchicken.com>

	  * xdisp.c (try_scrolling): When computing the distance from the
	  scroll margin to PT, try moving some distance past the window
	  bottom before giving up.

Interestingly, this change introduced an asymmetry between scrolling
down and up: there's no such limitation in the latter case.

The archives of emacs-devel do not reveal any details beyond the fact
that this was done to prevent some jumpy scrolling.  Perhaps Yidong
can shed more light on why this was done back then.  (The reason I
care is that I'd like to make sure my change now doesn't break
anything, since the emacs-devel archives don't show any test cases.)