Re: moving point and scroll-conservatively

[Juanma Barranquero <lekktu@gmail.com>]

On Sat, Jun 26, 2010 at 13:34, Eli Zaretskii <eliz@gnu.org> wrote:

> Did any of you who set scroll-conservatively to most-positive-fixnum
> notice that moving around an unmodified buffer became much slower,
> since revno 100620, when point moves far away?

No, I hadn't noticed.

> it takes Emacs 17 seconds on my 3GHz machine to display xdisp.c around
> line 25000, whereas it's instantaneous in Emacs 23.2.

It takes ~10s on my 2.5GHz Core2Quad Q9300. Which is ~10s longer than
it takes in 23.2, yes :-(

> Note that the documentation of
> scroll-conservatively explicitly says "set it to some small number N";
> i.e. it was never the intent that it will be set to such large values.

The documentation is in conflict because, as I already pointed out,
the docstring for `scroll-step' clearly says:

  If you want scrolling to always be a line at a time, you should set
  `scroll-conservatively' to a large value rather than set this to 1.

which is what prompted me to set it to most-positive-fixnum in the
first place. Perhaps, once the implementation is working as expected,
we should simply add an option scroll-never-recenter or somesuch.

> Btw, what do users of scroll-conservatively = most-positive-fixnum
> want from C-v and PageDown keys?  Is it okay to recenter in that case,
> or do you want to see the cursor on the last screen line in that case
> as well?

IIUC, if PgDown recenters, PgDown/PgUp will no longer be a noop (I set
`scroll-preserve-screen-position' to `always'), which would be pretty
bad.

All in all, I would prefer for Emacs *never* recenter unless I ask it
explicitly via C-l.

Thanks for all the hard work on this issue.

    Juanma