Re: Emacs 22.1 does not redisplay while holding down Prior key (scroll-down)

Re: Emacs 22.1 does not redisplay while holding down Prior key (scroll-down)

[Richard Stallman]

    When holding down the Prior key (usually labeled ?Page Up?) which is
    bound to scroll-down to scroll toward the start of the buffer, no
    redisplay occurs until the beginning of the buffer is reached.

    I see the same problem with Emacs from CVS from 2005-02.

    In Emacs 21.4, redisplay occurs after every movement with both keys,
    as expected.

This probably is due to a slowdown in redisplay compared with Emacs 21.

If someone figures out the cause of the slowdown, maybe we can speed up
that case.

Re: Emacs 22.1 does not redisplay while holding down Prior key (scroll-down)

[Stefan Monnier]

>     When holding down the Prior key (usually labeled ?Page Up?) which is
>     bound to scroll-down to scroll toward the start of the buffer, no
>     redisplay occurs until the beginning of the buffer is reached.

Is it the case everywhere?  E.g, also in fundamental-mode buffers?


        Stefan

Re: Emacs 22.1 does not redisplay while holding down Prior key (scroll-down)

[Joe Wells]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> When holding down the Prior key (usually labeled “Page Up”) which
>> is bound to scroll-down to scroll toward the start of the buffer,
>> no redisplay occurs until the beginning of the buffer is reached.
>
> Is it the case everywhere?  E.g, also in fundamental-mode buffers?

Yes, the problem occurs in fundamental mode in a fresh “emacs -Q”.

I just did some more testing, and the problem shows up for buffers
with very long lines.  It doesn't seem to happen for buffers with
lines less than 80 characters long.

To reproduce the bug, run these shell commands:

  wget http://codevortex.com/lovecraft/c_d_ward.htm
  emacs -Q c_d_ward.htm

Then in the Emacs frame, type M-x fundamental-mode RET M->.  Then
press and hold the Prior key.

Usually when I do this there is no redisplay until the beginning of
the buffer is reached.  Sometimes there are one or even two
redisplays.  In contrast, when using the Next key to go forward
starting from the beginning of the buffer, there are lots of
redisplays.

I wonder why scrolling backward would have the problem while scrolling
forward does not.  In Emacs 21.4 both directions of scrolling got good
redisplays.

By the way, for comparison, I don't see the problem on a plain text
variant of the c_d_ward.htm file with all lines less than 80
characters long.

-- 
Joe