unpleasant flickering in terminal emacs

unpleasant flickering in terminal emacs

[Amos Bird]

Hi,

I'm using emacs master branch in terminal (alacritty). When moving
cursor with relative line number enabled or scrolling up/down, I 
get
unpleasant screen flickering. However, frame switch works fine, 
which
I suppose uses full rendering updates. It seems partial rendering
update doesn't work well. The author of alacritty mentioned one
possible cause : "flickering is typically caused by a program not
writing full updates to the pty. We drain all available bytes up 
to
like 64k before yielding for a render. It may be that we should 
add
some heuristic around time to prevent flickering from poorly 
behaved
terminal applications." So my question is, can I enable full 
updates
for every redisplay? Thanks!

Here is a screencast of flickering.

https://youtu.be/wv4QINKHDUY

regards,

--
Amos Bird
amosbird@gmail.com

Re: unpleasant flickering in terminal emacs

[Tim Visher]

I don't have an informed idea about whether you're suffering from this (I
never have) but your question tickled my memory.

https://www.facebook.com/notes/daniel-colascione/buttery-smooth-emacs/10155313440066102/

On Fri, Apr 27, 2018 at 7:58 AM, Amos Bird <amosbird@gmail.com> wrote:

> Hi,
>
> I'm using emacs master branch in terminal (alacritty). When moving
> cursor with relative line number enabled or scrolling up/down, I get
> unpleasant screen flickering. However, frame switch works fine, which
> I suppose uses full rendering updates. It seems partial rendering
> update doesn't work well. The author of alacritty mentioned one
> possible cause : "flickering is typically caused by a program not
> writing full updates to the pty. We drain all available bytes up to
> like 64k before yielding for a render. It may be that we should add
> some heuristic around time to prevent flickering from poorly behaved
> terminal applications." So my question is, can I enable full updates
> for every redisplay? Thanks!
>
> Here is a screencast of flickering.
>
> https://youtu.be/wv4QINKHDUY
>
> regards,
>
> --
> Amos Bird
> amosbird@gmail.com
>
>

Re: unpleasant flickering in terminal emacs

[Amos Bird]

Thanks. But it's emacs in the terminal which flickers, not in the 
GUI. I'm not
sure if the double buffering mechanism has anything to do with 
terminals.

regards,

Tim Visher <tim.visher@gmail.com> writes:

> I don't have an informed idea about whether you're suffering 
> from this (I
> never have) but your question tickled my memory.
>
> https://www.facebook.com/notes/daniel-colascione/buttery-smooth-emacs/10155313440066102/
>
> On Fri, Apr 27, 2018 at 7:58 AM, Amos Bird <amosbird@gmail.com> 
> wrote:
>
>> Hi,
>>
>> I'm using emacs master branch in terminal (alacritty). When 
>> moving
>> cursor with relative line number enabled or scrolling up/down, 
>> I get
>> unpleasant screen flickering. However, frame switch works fine, 
>> which
>> I suppose uses full rendering updates. It seems partial 
>> rendering
>> update doesn't work well. The author of alacritty mentioned one
>> possible cause : "flickering is typically caused by a program 
>> not
>> writing full updates to the pty. We drain all available bytes 
>> up to
>> like 64k before yielding for a render. It may be that we should 
>> add
>> some heuristic around time to prevent flickering from poorly 
>> behaved
>> terminal applications." So my question is, can I enable full 
>> updates
>> for every redisplay? Thanks!
>>
>> Here is a screencast of flickering.
>>
>> https://youtu.be/wv4QINKHDUY
>>
>> regards,
>>
>> --
>> Amos Bird
>> amosbird@gmail.com
>>
>>


--
Amos Bird
amosbird@gmail.com

Re: unpleasant flickering in terminal emacs

[Eli Zaretskii]

> From: Amos Bird <amosbird@gmail.com>
> Date: Fri, 27 Apr 2018 19:58:56 +0800
> 
> I'm using emacs master branch in terminal (alacritty). When moving
> cursor with relative line number enabled or scrolling up/down, I 
> get unpleasant screen flickering.

Relative line numbers require a full redraw of the window when you
scroll, because every line's number changes.  Emacs will actually
redraw only the numbers themselves, and maybe also some general window
decorations.

Not sure why that happens to you during scrolling without line
numbers, it doesn't seem to happen to me.  Do you see that in
"emacs -Q"?

Re: unpleasant flickering in terminal emacs

[Eli Zaretskii]

> From: Amos Bird <amosbird@gmail.com>
> Date: Fri, 27 Apr 2018 20:23:07 +0800
> Cc: help-gnu-emacs <help-gnu-emacs@gnu.org>
> 
> I'm not sure if the double buffering mechanism has anything to do
> with terminals.

Indeed, it doesn't.

Re: unpleasant flickering in terminal emacs

[Amos Bird]

Hi Eli, "emacs -Q" works fine, same as my emacs's *scratch* buffer 
with 100K
lines of code. However, after switching to Fundamental mode and 
turning of
font-lock-mode, xdisp.c buffer still flickers while scrolling. All 
the minor
modes are the same as the *scratch* buffer. I've also tried 
loading the same
theme of "emacs -Q", it doesn't help either.


Eli Zaretskii <eliz@gnu.org> writes:

>> From: Amos Bird <amosbird@gmail.com>
>> Date: Fri, 27 Apr 2018 19:58:56 +0800
>>
>> I'm using emacs master branch in terminal (alacritty). When 
>> moving
>> cursor with relative line number enabled or scrolling up/down, 
>> I
>> get unpleasant screen flickering.
>
> Relative line numbers require a full redraw of the window when 
> you
> scroll, because every line's number changes.  Emacs will 
> actually
> redraw only the numbers themselves, and maybe also some general 
> window
> decorations.
>
> Not sure why that happens to you during scrolling without line
> numbers, it doesn't seem to happen to me.  Do you see that in
> "emacs -Q"?


--
Amos Bird
amosbird@gmail.com

Re: unpleasant flickering in terminal emacs

[Emanuel Berg]

Amos Bird wrote:

> I'm using emacs master branch in terminal
> (alacritty).

I read about alacritty a while back but haven't
used it and I don't remember what it said about
it. It was in Linux Magazine, I think.
Anyway I'm an Emacs terminal user as well, the
Linux VTs, I have Emacs 24/7 in /dev/tty1, and
I haven't experienced any flickering, so
perhaps it is an alacritty, and not terminal,
issue? What happens if you run Emacs from
a Linux VT? If you're on Linux that is?

-- 
underground experts united
http://user.it.uu.se/~embe8573

Re: unpleasant flickering in terminal emacs

[Eli Zaretskii]

> From: Amos Bird <amosbird@gmail.com>
> Cc: help-gnu-emacs@gnu.org
> Date: Fri, 27 Apr 2018 23:05:06 +0800
> 
> Hi Eli, "emacs -Q" works fine, same as my emacs's *scratch* buffer 
> with 100K
> lines of code. However, after switching to Fundamental mode and 
> turning of
> font-lock-mode, xdisp.c buffer still flickers while scrolling. All 
> the minor
> modes are the same as the *scratch* buffer. I've also tried 
> loading the same
> theme of "emacs -Q", it doesn't help either.

Sorry, I don't think I follow.  If you start Emacs with "emacs -Q",
then visit xdisp.c and scroll, does it still flicker?  If not, are you
saying that it starts flickering as soon as you load some theme?  If
so, what theme do you need to load?

Re: unpleasant flickering in terminal emacs

[Amos Bird]

Sorry for being ambiguous. I referred "my emacs" as the emacs with 
my
configuration instead of "emacs -Q".

regards,

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Amos Bird <amosbird@gmail.com>
>> Cc: help-gnu-emacs@gnu.org
>> Date: Fri, 27 Apr 2018 23:05:06 +0800
>>
>> Hi Eli, "emacs -Q" works fine, same as my emacs's *scratch* 
>> buffer
>> with 100K
>> lines of code. However, after switching to Fundamental mode and
>> turning of
>> font-lock-mode, xdisp.c buffer still flickers while scrolling. 
>> All
>> the minor
>> modes are the same as the *scratch* buffer. I've also tried
>> loading the same
>> theme of "emacs -Q", it doesn't help either.
>
> Sorry, I don't think I follow.  If you start Emacs with "emacs 
> -Q",
> then visit xdisp.c and scroll, does it still flicker?  If not, 
> are you
> saying that it starts flickering as soon as you load some theme? 
> If
> so, what theme do you need to load?


--
Amos Bird
amosbird@gmail.com

Re: unpleasant flickering in terminal emacs

[Amos Bird]

Hi, it also flickers in xterm, st, urxvt, termite ...

Emanuel Berg <moasen@zoho.com> writes:

> Amos Bird wrote:
>
>> I'm using emacs master branch in terminal
>> (alacritty).
>
> I read about alacritty a while back but haven't
> used it and I don't remember what it said about
> it. It was in Linux Magazine, I think.
> Anyway I'm an Emacs terminal user as well, the
> Linux VTs, I have Emacs 24/7 in /dev/tty1, and
> I haven't experienced any flickering, so
> perhaps it is an alacritty, and not terminal,
> issue? What happens if you run Emacs from
> a Linux VT? If you're on Linux that is?


--
Amos Bird
amosbird@gmail.com

Re: unpleasant flickering in terminal emacs

[Emanuel Berg]

Amos Bird wrote:

> it also flickers in xterm, st, urxvt, termite
> ...

OK, those are terminal emulators running in X.

-- 
underground experts united
http://user.it.uu.se/~embe8573

Re: unpleasant flickering in terminal emacs

[Eli Zaretskii]

> From: Amos Bird <amosbird@gmail.com>
> Cc: help-gnu-emacs@gnu.org
> Date: Sat, 28 Apr 2018 00:45:18 +0800
> 
> 
> Sorry for being ambiguous. I referred "my emacs" as the emacs with 
> my
> configuration instead of "emacs -Q".

Then I take it as meaning that "emacs -Q" doesn't show the problem,
even if you load the theme you are normally using?  If so, I suggest
to bisect your customizations to find out which one(s) cause this
flickering, then come back here and tell what you found.

Re: unpleasant flickering in terminal emacs

[Emanuel Berg]

Eli Zaretskii wrote:

> Then I take it as meaning that "emacs -Q"
> doesn't show the problem, even if you load
> the theme you are normally using? If so,
> I suggest to bisect your customizations to
> find out which one(s) cause this flickering,
> then come back here and tell what you found.

Is there an Emacs FAQ? (Of course there is.
Somewhere in Emacs!) The first question should
be,

   Q: I have a problem when I [insert the rest
      of your question here]
      
   A: run Emacs like this

        $ emacs -Q

      does the problem remain?

I guess this is an inherent problem with all
software that is based on customization and
extension, and where that happens in text files
that contain code. (Now it sounds like I have
tons of such software. And maybe I do...)

In practice, I have not experienced this as
a problem. I can find the bug in all my init
files because they are loaded by theme. So to
do binary search does not mean commenting out
half the code in a single enormous file (that
itself contains comments/"sections as
comments").

But that's the mere technical side to searching
of course. With time, one gets better at
finding the problem by thinking at the same
time as one does a brute-force attempt.
That's why the fighters that can punch AND
think are the best. Or carpenters for
that matter!

The only exception to the rule "isolating the
problem isn't difficult" that I have
encountered is with Gnus. Because leave out the
configuration, and you can't get to your
e-mail, or to any newsgroups, so you can't
reproduce the error w/o the Gnus your
init files!

Perhaps one should do like the LaTeX people
with their hangup on "minimal working
examples", namely, write a "minimal Gnus init
file" that does that and only that, namely
connects to ONE mailbox, and a single NNTP
newsgroup, and one Gmane/NNTP ditto, and why
not the .test ones while at it?

Then one could say, OK, so Gnus works. But not
my Gnus!

-- 
underground experts united
http://user.it.uu.se/~embe8573

Re: unpleasant flickering in terminal emacs

[Amos Bird]

It seems related to the true color terminfo I used.

xterm-24bits|xterm with 24-bit direct color mode,
   use=xterm-256color,
   setb24=\E[48;2;%p1%{65536}%/%d;%p1%{256}%/%{255}%&%d;%p1%{255}%&%dm,
   setf24=\E[38;2;%p1%{65536}%/%d;%p1%{256}%/%{255}%&%d;%p1%{255}%&%dm,

using xterm-256color doesn't flicker at all.

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Amos Bird <amosbird@gmail.com>
>> Cc: help-gnu-emacs@gnu.org
>> Date: Sat, 28 Apr 2018 00:45:18 +0800
>>
>>
>> Sorry for being ambiguous. I referred "my emacs" as the emacs 
>> with
>> my
>> configuration instead of "emacs -Q".
>
> Then I take it as meaning that "emacs -Q" doesn't show the 
> problem,
> even if you load the theme you are normally using?  If so, I 
> suggest
> to bisect your customizations to find out which one(s) cause 
> this
> flickering, then come back here and tell what you found.


--
Amos Bird
amosbird@gmail.com

Re: unpleasant flickering in terminal emacs

[Eli Zaretskii]

> From: Emanuel Berg <moasen@zoho.com>
> Date: Fri, 27 Apr 2018 22:38:25 +0200
> 
> Is there an Emacs FAQ? (Of course there is.
> Somewhere in Emacs!) The first question should
> be,
> 
>    Q: I have a problem when I [insert the rest
>       of your question here]
>       
>    A: run Emacs like this
> 
>         $ emacs -Q
> 
>       does the problem remain?

People who discover something important frequently want that to be the
first issue described in <THE DOCUMENT OF YOUR CHOICE>.  Of course,
there's only one such issue that can ever be the first one in any
document...

Emacs does have a FAQ (two of them, actually), but our documentation
principles are that such fundamental issues should be in the manual,
not in the FAQ.

The Emacs manual has a chapter on reporting bugs, which begins with
explaining how to establish there's a bug and how to search the list
of known problems.  Then it describes how to report a bug, and as part
of that tells about "emacs -Q".

> The only exception to the rule "isolating the
> problem isn't difficult" that I have
> encountered is with Gnus. Because leave out the
> configuration, and you can't get to your
> e-mail, or to any newsgroups, so you can't
> reproduce the error w/o the Gnus your
> init files!

The "start with 'emacs -Q'" rule doesn't mean you cannot load
additional packages, set variables to non-default values, etc.  The
idea is to present a full recipe starting from 'emacs -Q', so that
others could reproduce that without knowing anything about the Emacs
setup on the OP's system.

> Perhaps one should do like the LaTeX people
> with their hangup on "minimal working
> examples", namely, write a "minimal Gnus init
> file" that does that and only that, namely
> connects to ONE mailbox, and a single NNTP
> newsgroup, and one Gmane/NNTP ditto, and why
> not the .test ones while at it?

Exactly.  Except that if the problem doesn't need a Gnus init file at
all, you don't even need such a minimal file as part of the recipe.
You can just show which variables should be set to what values,
manually.

Re: unpleasant flickering in terminal emacs

[Eli Zaretskii]

> From: Amos Bird <amosbird@gmail.com>
> Cc: help-gnu-emacs@gnu.org
> Date: Sat, 28 Apr 2018 11:36:37 +0800
> 
> It seems related to the true color terminfo I used.
> 
> xterm-24bits|xterm with 24-bit direct color mode,
>    use=xterm-256color,
>    setb24=\E[48;2;%p1%{65536}%/%d;%p1%{256}%/%{255}%&%d;%p1%{255}%&%dm,
>    setf24=\E[38;2;%p1%{65536}%/%d;%p1%{256}%/%{255}%&%d;%p1%{255}%&%dm,
> 
> using xterm-256color doesn't flicker at all.

Thanks, please report this as a bug using "M-x report-emacs-bug RET".

Re: unpleasant flickering in terminal emacs

[Emanuel Berg]

Eli Zaretskii wrote:

> People who discover something important
> frequently want that to be the first issue
> described in <THE DOCUMENT OF YOUR CHOICE>.
> Of course, there's only one such issue that
> can ever be the first one in any document...

The first question should be "What is Emacs?"

The first answer on debugging should be "-Q" in
order to find out if the problem is with Emacs
or in the user's setup.

People who have problems with Emacs and come
here and ask about it sometimes get a bit
embarrassed when trying -Q to find out the
problem is with them and not with Emacs.
This Q&A in a FAQ could spare some of them this
experience.

But actually I don't think it is anything to be
embarrassed about. Furthermore they might still
need help with their situation. And really, if
all such cases really were Emacs bugs, that'd
be even more embarrassing :)

-- 
underground experts united
http://user.it.uu.se/~embe8573