[PATCH 2/2] protocol: add state set functions for maximized and fullscreen.

Jason Ekstrand jason at jlekstrand.net
Sat Nov 2 04:59:04 CET 2013

On Fri, Nov 1, 2013 at 8:36 PM, Gregory Merchan
<gregory.merchan at gmail.com>wrote:

> On Thu, Oct 31, 2013 at 8:28 PM, Jason Ekstrand <jason at jlekstrand.net>
> wrote:
> > On Thu, Oct 31, 2013 at 3:37 PM, Bill Spitzak <spitzak at gmail.com> wrote:
> >>
> >> Jason Ekstrand wrote:
> >>
> >>> Yes, in theory they could read the configuration of the compositor.
> >>
> >>
> >>> I really don't want to build this kind of inconsistency into the system
> >>> and I don't see why it's justified.
> >>
> >>
> >> I think I see what you are getting at. I think a scheme that allows
> simple
> >> applications to obey the global setting without thinking, but still
> allows
> >> applications that have a good reason to do tricks with the focus, and
> also
> >> matches the raise proposal, is this:
> >>
> >> - The compositor sends an "I want you to activate" event, as you
> propose.
> >> - The client can respond to this with an "activate" request. Or it could
> >> send an "activate" request at other times if it wants.
> >> - The compositor responds to the "activate" request by either ignoring
> it
> >> or actually doing the activation.
> >> - The compositor sends an "activated" event that the client can respond
> to
> >> by redrawing to show the fact that they are activated.
> >>
> >> If a client just echoes the "I want you to activate" event then it will
> >> work as you expect. A client could also wait after the event until the
> mouse
> >> enters a correct location or clicks on the right thing. It could also
> try to
> >> generate spurious activates but the compositor may ignore them.
> >>
> >
> > I still don't understand why a client would want to not activate.  I can
> see
> > not wanting to raise, but why not activate?
> As Bill mentioned in a follow-up, drag sources would want to not activate.
> This can be handled more simply than described above, without a
> special "activate" system. I assume "activation" applies to a window,
> not a client.
> First, clients are responsible for requesting activation when it is
> appropriate.
> Second, the compositor always activates when it is appropriate.
> The complicated part is determining what is appropriate.
> There are 5 activation policies. For each policy, the compositor
> activates windows as needed for key traversal (e.g. Alt+Tab), task bar
> actions, when an active window goes away, viewport changes, etc. The
> compositor also activates windows when a request for activation has
> the correct signature. The policies are distinguished by special cases
> for activation or deactivation:
> 1. PointerRoot: Activates a window when the pointer enters it and
> deactivates it when the pointer leaves.
> 2. Sloppy: Activates a window when the pointer enters it.
> 3. Delayed sloppy: Activates a window when the pointer has been within
> for a short time.
> 4. Click-to-focus: Activates a window when it is clicked.
> 5. Windows/MacOS-style: Does not activate a window, except as it does
> for all policies.
> (I suppose a "Delayed PointerRoot" policy is possible, but I've never
> seen any discussion of it.)
> For each of these policies, another distinction may be made according
> to signature required to honor an activation request. The strictest
> form is to deny all requests, which is not possible on X11 because
> there is no redirection for focus changes. An often desired form for
> the correct signature, among X11 users, is that the request must come
> from a client which is already activated. For example, this allows an
> active program to activate a dialog, but prevents other programs from
> activating any windows. Unless I am mistaken, most attempts at "focus
> stealing prevention" have aimed at such a policy. I'm pretty sure I've
> seen at least one window manager that will fight with bad programs to
> enforce such a policy. On X11, the correct signature is always only
> that the timestamp is later than the last focus change timestamp, and
> this may be achieved by using CURRENT_TIME. Convention is relied upon
> to avoid chaos, that convention is that clients must always use a
> valid timestamp to set focus, and there are 4 sources of valid
> timestamps: 1) button events, 2) key events, 3) property change
> events, and 4) a window manager message. This last source exists to
> address the lack of a timestamp in the focus change event of the X
> protocol. I will refer to this as the "valid event" signature.
> Wayland is a different system and there are more options for the
> signature requirement. If I understand the protocol correctly, the
> serial field of pointer, keyboard, and touch events could be used as a
> signature. (Like X, wl_keyboard::enter does not have a time argument,
> so that is not an option.) The strictest form of these
> policies--denying all requests--can be achieved because the compositor
> is in control; it's like a window manager and an X server combined in
> that sense. The "must be active" signature can be implemented by
> checking that the serial number came from an event sent to an active
> client. The valid event signature can be implemented by checking that
> the serial number came from a wl_pointer::button event, a
> wl_keyboard::key event, a wl_keyboard::enter event, or wl_touch::down
> event.
> The compositor is always in control, so clients can request activation
> as much as they like without messing things up. Clients cannot prevent
> the compositor from implementing any of the five activation policies.
> The first four policies require nothing from clients to work as
> expected; they are what we've had on X forever. The last policy does
> not work unless clients request activation as needed when they have a
> valid event. To my knowledge, both Windows and MacOS already require
> applications to request activation in this way, so cross-platform
> toolkits don't have to make a special case. This is the first
> requirement that was stated before: clients are responsible for
> requesting activation when it is appropriate.
> I have said nothing about stacking. Handling activation as I have
> described allows for every kind of stacking behavior I've seen, except
> for one: raise on frame clicks, but not on clicks within the frame.
> This exception exists when the compositor is not responsible for
> drawing the window frame, because nothing I have described allows the
> compositor to distinguish between parts of the client window. Make
> that distinction and the problem is solved; choose whichever stacking
> policy you would like. If the distinction between the frame and the
> rest of the window is included in the request for activation, you can
> even have clicks in the client raise, but only clicks on the frame
> activate, though I can think of no reason beyond sadism why anyone
> would make things work that way.
> I believe a simple stacking policy would be to allow a client with an
> active window to do anything it wants with its windows within the
> bounds set by other features; basically it can do anything as long as
> it doesn't put windows below stay-on-bottom features, like the
> desktop, or above stay-on-top features, like task bars and menus. I
> believe it would be sensible to keep the active window on top within
> its bounds, excepting for secondary windows, like tool palettes, which
> should stay above the primary window. This is the stacking behavior
> familiar to users of Windows and MacOS. I emphasize that the stacking
> policy is independent of the activation policy, so long as the
> compositor can distinguish between frames and their contents.
> The guides I gave before--clients request activation responsibly,
> compositors activate appropriately--allow all users to use their
> chosen compositors with any application targeted at Wayland.
> The combination of Windows/MacOS-style activation policy with an
> active-window-on-top stacking policy is the behavior familiar to
> Windows and MacOS users, including the allowance for beginning a
> drag-and-drop operation without raising the drag source window. Much
> the same system is possible on X11 if window managers will not grab
> buttons without modifiers and regular clients will use the globally
> active input model, requesting input focus when appropriate. Perhaps
> most important to many reading this list is that the all the
> activation policies familiar from X are compatible with the client
> behavior I have described.
> When I'm done with my current project at work, I'll be able to see
> about writing code for what I have described, but that's weeks or
> months away and then I'll need time to reacquaint myself with pretty
> much everything. I hope that this has been a useful message. I
> apologize for the lengthy lack of code.

Thank you very much for your e-mail.  I think that helps a lot.  The lack
of code is ok because I think Rafael is planning to start implementing as
soon as things settle a bit.  Sometimes protocol discussions can end up
with a whole lot of hypotheticals and what you gave was a very clear
concise discussion of the topic.

If I am understanding you correctly, what we need are an "activate" request
and "notify_active" and "notify_inactive" events.  To support sloppy focus,
clients should just always try to activate on wl_pointer.enter and let the
compositor sort it out unless they have a good reason to do otherwise.  For
cases such as alt-tab, or another window closing, the compositor simply
sends a notify_active.  I think I'm ok with this.

Two more questions that come to mind:

1) Will we ever need a deactivate request?  Under the given scheme, no need
comes immediately to mind.

2) Should the activate be associated with a particular seat.  If you have
multiple cursors, you can easily have multiple active windows so this seems
perfectly reasonable.  If this is the case, should this be part of wl_seat
or should we keep it in xdg_shell?  I'm a little afraid to clutter wl_seat
unnecessarily but this is very quickly starting to look like a seat focus.

Once again, Gregory, Thanks for the explanation.  I hope I'm following ok.
--Jason Ekstrand
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