GNU bug report logs - #12937
24.2; Fontification performed in 'jit-lock-defer-time' in any case (don't wait while Emacs become really idle).

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Kangas <stefan <at> marxist.se>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#12937: closed (24.2; Fontification performed in
 'jit-lock-defer-time' in any case (don't wait while Emacs become really
 idle).)
Date: Fri, 17 Apr 2020 10:25:02 +0000

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Your message dated Fri, 17 Apr 2020 12:24:07 +0200
with message-id <87sgh2tnp4.fsf <at> stefankangas.se>
and subject line Re: bug#12937: 24.2; Fontification performed in 'jit-lock-defer-time' in any case (don't wait while Emacs become really idle).
has caused the debbugs.gnu.org bug report #12937,
regarding 24.2; Fontification performed in 'jit-lock-defer-time' in any case (don't wait while Emacs become really idle).
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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From: Oleksandr Gavenko <gavenkoa <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.2;
	Fontification performed in 'jit-lock-defer-time' in any case (don't
	wait while Emacs become really idle).
Date: Mon, 19 Nov 2012 22:56:26 +0200

I open (a very long .c file):

  emacs-bzr/trunk/src/coding.c

and hold DOWN key. Text in buffer scrolls up but with jerks (random stops of
scrolling for a little time) due to fontification actions.

From 'jit-lock-defer-time' docs:

  Idle time after which deferred fontification should take place.
  If nil, fontification is not deferred.

I would try to workaround jerks with:

  (setq jit-lock-defer-time 0.01)

and with same negative effect by (see below):

  (setq jit-lock-defer-time 3.0)

When I hold DOWN key text scrolls up with jerks again! Because fontification
performed again.

I expect that when I *hold* key Emacs in not idle (it get user input and
redisplay text!!) so don't understand why fontification take place. May be I
misunderstand idling concept in Emacs and should read manuals deeper...

Also note that fixing CC-mode is not a solution as there are many possible
external modes that can be useful but with slow fontification.

So it is good to have 'jit-lock-defer-time' behaviour that allow trick with
defer fontification.

I know some peoples use workflow when they use scroll-bars for very fast
moving around a file (to get brief look of file content). I prefer use
PageUp/PageDown keys to perform this task.

In GNU Emacs 24.2.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.10)
 of 2012-09-09 on trouble, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11204000

-- 
Best regards!

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From: Stefan Kangas <stefan <at> marxist.se>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 12937-done <at> debbugs.gnu.org, Stefan Monnier <monnier <at> iro.umontreal.ca>,
 Oleksandr Gavenko <gavenkoa <at> gmail.com>
Subject: Re: bug#12937: 24.2;
 Fontification performed in 'jit-lock-defer-time' in any case (don't
 wait while Emacs become really idle).
Date: Fri, 17 Apr 2020 12:24:07 +0200

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> Stefan Monnier <monnier <at> iro.umontreal.ca> writes:
>
>> I don't see that.  I'm not sure how you tried, it but I did
>>
>>   src/emacs -Q --eval '(setq jit-lock-defer-time 0.01)' src/xdisp.c
>>
>> and scrolling with page-down indeed is jerky and I see that the buffer
>> is getting fontified (at least occasionally).  But if I try again with
>>
>>   src/emacs -Q --eval '(setq jit-lock-defer-time 0.1)' src/xdisp.c
>>
>> then the scrolling is fast&smooth and it only gets fontified when
>> I stop scrolling.
>
> I tried this in Emacs 27 (on a pretty fast laptop), and I got no
> jerkiness when holding <down> (and things are fontified as I scroll).  I
> also tried 0.001.
>
> So is this still a problem?

More information was requested, but none was given within 6 months, so
I'm closing this bug.  If this is still an issue, please reply to this
email (use "Reply to all" in your email client) and we can reopen the
bug report.

Best regards,
Stefan Kangas

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