Re: Why do idle timers trigger redisplay?

Re: Why do idle timers trigger redisplay?

[Eli Zaretskii]

> Date:  Thu, 11 Feb 2016 16:14:44 -0800
> From:  Keith David Bershatsky <esq@lawlist.com>
> Cc:  22404@debbugs.gnu.org
> 
> Question, please:  Is it a necessary evil that the `timer-idle-list` must always trigger a redisplay?

Emacs does another redisplay cycle each time there was some kind of
input.  The logic of this is that any input could potentially affect
what is displayed (the job of figuring out what, if anything, does
need to be redrawn is integral part of what redisplay does, and it
might as well conclude that no redisplay is actually needed).

Code run by timers is one such kind of input, since any code run by
timers runs with the purpose of doing something with Emacs data:
buffers, strings, windows, frames, etc.

Other kinds of input include: keyboard input, input from subprocesses,
mouse gestures, events that come from sources like D-bus and file
notifications, etc.  They all cause a cycle of redisplay.

Re: Why do idle timers trigger redisplay?

[Keith David Bershatsky]

Thank you, Eli, for helping me to better understand why code run by timers is considered input that triggers redisplay (which in turn figures out what to do).

As always, your tutoring is greatly appreciated.

Keith

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At Fri, 12 Feb 2016 10:25:51 +0200,
Eli Zaretskii wrote:
> 
> > Date:  Thu, 11 Feb 2016 16:14:44 -0800
> > From:  Keith David Bershatsky <esq@lawlist.com>
> > 
> > Question, please:  Is it a necessary evil that the `timer-idle-list` must always trigger a redisplay?
> 
> Emacs does another redisplay cycle each time there was some kind of
> input.  The logic of this is that any input could potentially affect
> what is displayed (the job of figuring out what, if anything, does
> need to be redrawn is integral part of what redisplay does, and it
> might as well conclude that no redisplay is actually needed).
> 
> Code run by timers is one such kind of input, since any code run by
> timers runs with the purpose of doing something with Emacs data:
> buffers, strings, windows, frames, etc.
> 
> Other kinds of input include: keyboard input, input from subprocesses,
> mouse gestures, events that come from sources like D-bus and file
> notifications, etc.  They all cause a cycle of redisplay.

Re: Why do idle timers trigger redisplay?

[Stefan Monnier]

> Thank you, Eli, for helping me to better understand why code run by timers
> is considered input that triggers redisplay (which in turn figures out what
> to do).

Presumably idle timers have effects (their return value is ignored, so
if they have no effect they're useless).  So they may change buffers or
elements that affect the mode-line.  So a redisplay cycle needs to be
triggered after running them.


        Stefan