bug#17404: Scrolling is painfully slow

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 06 May 2014 07:42:47 -0400
> From: Richard Stallman <rms@gnu.org>
> CC: 17404@debbugs.gnu.org
> 
> I should explain that I configured Emacs to visit that file in Rmail mode.
> Try it that way.

I did.  I used "C-u M-x rmail RET foo2.mail RET" in "emacs -Q".  Does
that reproduce the problem on your system?

What about "emacs -nw" -- do you see the same slowdown there?  Or is
the problem limited to the GUI sessions?

> I tried visiting it in 24.3.50.1 from May 1 2013.

Thanks, I'll try to see which change(s) could be responsible, but a
year is a lot in Emacs development, so if you could reduce the range,
it would help.

> Scrolling the file in Rmail mode is much faster in that version
> than in the current version.  So is C-n.

How much more faster?  Can you estimate the slowdown quantitatively?

> With find-file-literally it is almost instantaneous
> in both 24.3.50.1 and the current version.

find-file-literally disables bidirectional display, so it will always
result in faster redisplay.