[PATCH wayland] server: Make serial number 0 mean invalid

[Bill Spitzak]

On 10/13/2015 09:53 AM, Jasper St. Pierre wrote:
> The goal of focus-stealing prevention isn't to prevent hostile clients
> from stealing the focus. It's to allow friendly clients to upgrade the
> experience if they can track the originating event that originally
> opened a window. For instance, if I launch GIMP but then go back to
> typing in a terminal, after GIMP launches, it shouldn't steal the
> focus, because I've interacted with another window since then.
>
> We've tried turning off focus-stealing prevention for all new windows
> without a timestamp, and it provided a very unfun experience. Lots of
> applications either don't have an originating user action when they
> pop up a window, or they don't track it thoroughly.
>
> Perhaps GUI applications have gotten substantially better in the 6
> years ago since we tried it -- I'd be willing to run the experiment
> again. But I don't expect much changing.

Yes but this is still not answering my question.

Can you describe a design where no-event is treated *differently* than 
an unknown or disallowed event in the _present request?

You are describing how they would be treated identically. I suspect that 
will always happen, but the idea that they can be treated differently is 
being used as an excuse to not add the special no-event serial of zero 
and reduce the number of _present messages from 2 to 1.