[RFC : xdg_surface_present() - take 2

Thu Mar 26 22:54:36 PDT 2015

Hi Jasper, Jonas, Pekka, Jason,

Just a little update regarding the present() request. As the serial thing
seems to be our main concern, aside from the minor protocol change and new
functionality we mostly seem to agree on, here are the 2 ways we could do
it :

1) modify the protocol, which means :
- in the XML, adding : "A serial of 0 cannot be returned by the compositor
; thus in requests, passing 0 as a "serial" parameter actually means no
specific serial is needed nor provided."
- modify wayland-server to reflect the description (thanks to Jonas for
reminding me).

2) have 2 requests instead of 1 :
xdg_surface_present(struct xdg_surface *surface);
xdg_surface_present_from_event(struct xdg_surface *surface, uint32_t
serial);

What should be our preferred way ? Doing 2) is still satisfying is we
cannot do 1). Looking for a consensus here.

Regards,
Manuel

2015-03-09 6:17 GMT+01:00 Manuel Bachmann <
manuel.bachmann at open.eurogiciel.org>:

> Hi Jasper,
>
> "This is not an "I need attention" request. Perhaps our documentation is
> poor."
> You are right, just as I answered to Jonas, I mixed present() with the
> desktop-launcher-focus-stealing feature we were discussing in the previous
> thread. Sorry for the confusion.
>
> 2015-03-09 3:25 GMT+01:00 Jasper St. Pierre <jstpierre at mecheye.net>:
>
>>
>>
>> On Sun, Mar 8, 2015 at 6:57 PM, Jonas Ådahl <jadahl at gmail.com> wrote:
>>
>>> On Fri, Feb 27, 2015 at 11:14:19AM +0100, Manuel Bachmann wrote:
>>> > Hello fellow developers,
>>> >
>>> > I just wanted to continue a discussion which occured some time ago,
>>> about
>>> > the eventuality of adding a "xdg_surface_present()" request to
>>> XDG-Shell.
>>> >
>>> > (For reference, former discussion entry points are here :
>>> >
>>> http://lists.freedesktop.org/archives/wayland-devel/2014-July/016078.html
>>> >
>>> http://lists.freedesktop.org/archives/wayland-devel/2014-July/016224.html
>>> >
>>> http://lists.freedesktop.org/archives/wayland-devel/2014-August/016269.html
>>> )
>>> >
>>> > To summarize : the idea behing "xdg_surface_present()" is that there
>>> are
>>> > some cases where a surface wants to advertise the fact that it has been
>>> > updated and the user may want to take a look (think of an IRC chat
>>> window
>>> > which gets new messages containing the user's nickname). There are even
>>> > some corner cases where the surface may want to be raised and focused
>>> > directly ; but we do not want to request to be abused this way, a
>>> client
>>> > must be prevented from stealing the focus repeatedly. At last, the
>>> > compositor's shell should have the last word.
>>>
>>> I have some comments I thought I'd share. See the inline replies:
>>>
>>> >
>>> > Here are some of the points that were discussed and the outcomes :
>>> >
>>> > - Pekka Paalanen pointed out the request name was unclear and
>>> suggested to
>>> > use "xdg_surface_needs/wants_attention()" instead. Jasper St. Pierre
>>> > pointed out that "_NET_WM_STATE_DEMANDS_ATTENTION" already existed in
>>> X11
>>> > and does not do the same thing. We discussed that again yesterday and
>>> > thought that present() fitted nicely ;
>>>
>>> There is also the "The Present Extension" in X11, so is "present" really
>>> that much better? If the use case is a client wants attention because
>>> some reason (be it IRC highlight, new message, task finished or
>>> whatever), shouldn't the request name contain that information some how?
>>> Isn't what is discussed here even quite similar to
>>> "_NET_WM_STATE_DEMANDS_ATTENTION"?
>>>
>>
>> No. It's equivalent to the _NET_ACTIVATE_WINDOW ClientMessage.
>>
>> IRC highlights, new messages, task finished, etc. are use cases for
>> notifications. The use case here is "user double-clicked on a file and I
>> want my existing gedit window to be raised in response". Basically, places
>> where you want to show the window immediately if the stars are aligned
>> correctly (the serial is correct).
>>
>>
>>> >
>>> > - We want to implement focus stealing prevention : if the user is
>>> starting
>>> > a slow app (browser...), gets back to typing a mail while it starts,
>>> and at
>>> > last the browser window appears, the focus should stay in the mail
>>> window
>>> > without his keyboard presses going elsewhere ;
>>>
>>> This rather sound like something startup notification protocol related
>>> than an "I need attention" request, and I think that problem needs to be
>>> tackled separately.
>>>
>>
>> This is not an "I need attention" request. Perhaps our documentation is
>> poor.
>>
>>
>>> >
>>> > - Implementing focus stealing prevention between different clients may
>>> be
>>> > easy : just count the delay between the client has been started and its
>>> > shell surface actually gets mapped, and if it has been too long and the
>>> > focus is elsewhere, show the surface without focusing it (but with a
>>> > notification). The notion of "the client has been started" is vague,
>>> but at
>>> > worst, we can use the time when the client did its initial connection
>>> to
>>> > the compositor ;
>>>
>>> As Bill mentioned, clients that happens to do a lot of things before
>>> connecting will have a very short time from that the connection is
>>> established to that a surface is to be mapped. It can even be trivially
>>> abused to steal focus at unexpected times.
>>>
>>> >
>>> > - Within a same client application, however, it is harder. Think of a
>>> > browser where you click "new window" but lots of time pass before it
>>> > appears. The "starting point" is the pointer click event. So the idea
>>> would
>>> > be to pass the Wayland serial corresponding to this event :
>>> > "xdg_surface_present (surface, <SERIAL>)". It the serial has been
>>> issued
>>> > too long ago, do focus stealing prevention.
>>>
>>> Serials are quite easy to guess, but for intra-client focus switching it
>>> might work. I don't think it's a good idea to pass serials between
>>> clients and assume they have any effect, and the server should probably
>>> not allow such focus switching between clients.
>>>
>>> >
>>> > This raises the question : how do we say "We have no serial to pass",
>>> for
>>> > the standard case ? We repeatedly suggested 0 ("xdg_surface_present
>>> > (surface, 0)") because serials are incrementing globals, so "0" to be
>>> > issued would be very-very unlikely. Should we formalize that somewhere
>>> in
>>> > the protocol ?
>>>
>>> If 0-is-invalid its not formalized, it should not be relied upon IMO,
>>> but I think it is useful to have a non-valid serial.
>>>
>>>
>>> Jonas
>>>
>>> >
>>> > (Having 2 requests, one with serial and one without, has been
>>> suggested by
>>> > krh on IRC ; I personally prefer only one request because they would
>>> serve
>>> > the same purpose, but why not ? It would get the need for
>>> formalization out
>>> > of the way)
>>> >
>>> > We also want to secure the request from garbage random serials ; the
>>> > implementation behavior is that there is only one serial valid for a
>>> few
>>> > seconds, if the surface has not been focused for some time, it will
>>> not be
>>> > able to raise itself even if it random()ly finds the formerly "good"
>>> serial.
>>> >
>>> > -----
>>> > Now the demos ! Here is the latest code :
>>> >
>>> > https://github.com/Tarnyko/weston-xdg_surface_present/commits/test
>>> >
>>> > A video for the generic "focus stealing prevention" case (delayed
>>> start,
>>> > focus stays in old surface) between different clients :
>>> >
>>> > https://www.youtube.com/watch?v=gifjXyPV3X4
>>> >
>>> > and within the same client :
>>> >
>>> > https://www.youtube.com/watch?v=Xiq1p5AOf1U
>>> > -----
>>> >
>>> > Any thoughts on this ?
>>> >
>>> > --
>>> > Regards,
>>> >
>>> >
>>> >
>>> > *Manuel BACHMANN Tizen Project VANNES-FR*
>>>
>>> > _______________________________________________
>>> > wayland-devel mailing list
>>> > wayland-devel at lists.freedesktop.org
>>> > http://lists.freedesktop.org/mailman/listinfo/wayland-devel
>>>
>>> _______________________________________________
>>> wayland-devel mailing list
>>> wayland-devel at lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/wayland-devel
>>>
>>
>>
>>
>> --
>>   Jasper
>>
>
>
>
> --
> Regards,
>
>
>
> *Manuel BACHMANN Tizen Project VANNES-FR*
>

-- 
Regards,

*Manuel BACHMANN Tizen Project VANNES-FR*
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