bug#52085: 29.0.50; Frame occasionally fails to paint while screen sharing on macOS

[Aaron Jensen <aaronjensen@gmail.com>]

On Thu, Dec 9, 2021 at 2:27 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Aaron Jensen <aaronjensen@gmail.com>
> > Date: Wed, 8 Dec 2021 16:33:06 -0500
> >
> > > To be honest, if I just want to see when one function is called I
> > > stick in 'NSLog (@"Moo")' or whatever. There's too much output in
> > > NSTRACE and I'm sure that sometimes it doesn't print out results from
> > > things that are called deep in the toolkit code.
> >
> > Well, I can say with some certainty that those messages are the only
> > ones appearing under typical operations like key presses. I can insert
> > newlines into the terminal and observe that only those are emitted
> > when I press keys or even scroll. So the display function is not being
> > called unless there is some other wildness going on with the tracing.
> > Do you expect it to be called every render? (It is also not called
> > when I run M-: (redisplay))
>
> I'm not tracking this discussion, so apologies if what I say below
> makes no sense.  However, the Emacs display engine avoids redrawing
> anything if it concludes that what's on the glass is correct.  So just
> calling 'redisplay', or making some simple changes that don't require
> significant redrawing, don't necessarily result in calls to low-level
> drawing functions, you need to do something drastic to force those
> with 100% certainty.
>
> HTH

Even toggling between one buffer and another in a window fails to log
anything but:

nsterm.m  : 6100: [ 2953]  [EmacsView keyDown:]
nsterm.m  : 6393: [ 2954]  | [EmacsView hasMarkedText]
nsterm.m  : 6284: [ 2955]  | [EmacsView insertText:]
nsterm.m  : 6100: [ 2956]  [EmacsView keyDown:]

I'm probably missing something here...