bug#57434: 28.1.91; Terminal Emacs Mac OS flickering.

[Eli Zaretskii]

> From: Dmitrii Kuragin <kuragin@google.com>
> Date: Tue, 20 Sep 2022 09:35:41 -0700
> Cc: Gerd Möllmann <gerd.moellmann@gmail.com>, 
>       57434@debbugs.gnu.org
> 
> But could you please elaborate a bit more on what I can do now?
> 
> Do we want to add a hook like `begin_frame_update` or we need to add a
> `sync_update_begin_escape_code` or we just say, sync_update_protocol (we have 
> 2 of those now).

I think we want to add begin/end_frame_update hooks, and we want them
to send the escape sequences that are determined by some state
variable which tells us which of the 2 protocols to use.  We then need
a function to allow changing that state variable, perhaps by an
explicit user command.

Bonus points for making the state variable be terminal-specific, so
that the same Emacs session could have TTY frames on several different
types of terminal, and use the correct protocol for each one of them.

I hope I explained this well enough; if not, feel free to ask specific
questions.

> Alternatively, we can allow users to specify it as a terminal capability and 
> let them override it. Like, `(setq
> xterm-extra-capabilities (quote (modifyOtherKeys setSelection)))`

No, that's too dangerous, and not really needed.  It's not like there
are many different protocols for synchronized update.

Thanks.