* Buggy scroll-up (was: scroll-margin buggy on Emacs 21.1)
[not found] ` <m27k7prmjg.fsf@maui.hanak.hu>
@ 2003-06-15 10:06 ` Hanak David
2003-06-15 23:10 ` Buggy scroll-up Dan Jacobson
0 siblings, 1 reply; 2+ messages in thread
From: Hanak David @ 2003-06-15 10:06 UTC (permalink / raw)
Hi,
There was quite a bit of traffic about vertical scrolling hanging emacs
when scroll-margin is set. I tried to do a little research on the topic
and got the following.
Last time I wrote:
> Invoked "emacs -q --no-site-file", then I did
>
> M-x set-variable RET scroll-margin RET 2 RET
>
> Emacs locks up "only" when the last line of the buffer is visible in the
> window, but it is (strictly) closer to the bottom than scroll-margin and
> there are some blank lines, too. So, by setting s-m to 2, the problem
> occurs only when there is exactly one blank line at the bottom. [...]
I have to amend that: the problem occurs only in 21.* emacsen, and only if
scoll-margin*2 > next-screen-context-lines. So a workaround for everyone
is to set n-s-c-l to at least 2 * s-m. The behaviour of emacs in that case
is still funny at the end of buffers, but at least it doesn't lock up.
I also tried to debug it. The problem is (quite expectedly) in file
window.c, function window_scroll_pixel_based, lines 4126-4127.
,----[ window.c, lines 4121-4129 ]
| if (n > 0)
| {
| /* We moved the window start towards ZV, so PT may be now
| in the scroll margin at the top. */
| move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
| while (it.current_y < this_scroll_margin)
| move_it_by_lines (&it, 1, 1);
| SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
| }
`----
The while loop turns out to be an infinite loop, because move_it_by_lines
doesn't increase it.current_y.
I believe the problem is that when emacs tries to preserve lines from the
previous page, it is confused by the empty lines at the bottom of the
window. Howver, I don't exactly know how or why.
Would someone who's familiar with window.c go deeper into it? It is the
first time I'm looking at emacs source, so I wouldn't mind if this person
didn't have to be me.
David
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Buggy scroll-up
2003-06-15 10:06 ` Buggy scroll-up (was: scroll-margin buggy on Emacs 21.1) Hanak David
@ 2003-06-15 23:10 ` Dan Jacobson
0 siblings, 0 replies; 2+ messages in thread
From: Dan Jacobson @ 2003-06-15 23:10 UTC (permalink / raw)
By the way, I wonder if others also sometimes look up to notice the scroll bars have
disappeared. Version number in my headers.
^ permalink raw reply [flat|nested] 2+ messages in thread
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[not found] <3C7D593F.9080906@nnl.se>
[not found] ` <8361-Sun03Mar2002190054+0200-eliz@is.elta.co.il>
[not found] ` <m27k7prmjg.fsf@maui.hanak.hu>
2003-06-15 10:06 ` Buggy scroll-up (was: scroll-margin buggy on Emacs 21.1) Hanak David
2003-06-15 23:10 ` Buggy scroll-up Dan Jacobson
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