[PATCH] libweston-desktop: add signals for title, app_id

[Jonas Ådahl]

On Tue, Jul 25, 2017 at 06:42:34AM -0600, Matt Hoosier wrote:
> I'd find it a little bit inconvenient for the title, class, and app-id to
> be treated as buffered state. They make a great poor-man's way of
> identifying surfaces for embedded systems that implement simple layer
> management policies without wholesale adopting IVI shell (whose lack of
> wl_shell makes it difficult to integrate off-the-rack Wayland libraries and
> apps). Since the surface title doesn't have anything to do with correct
> graphical presentation, it'd be nicer if that data is just available
> immediately to the rest of the shell rather than being something that only
> trickles in whenever the app happens to post a buffer next.

There is no need to attach a new buffer to commit a new state. One could
for example commit a state only changing the title and nothing else, and
it'd be completely correct. The benefit of synchronizing it is for
example that a shell can synchronously change some overlay with the
content.

Regarding the app_id, the app_id should normally only ever be set once,
as part of the initial state that doesn't have a buffer attached yet.


Jonas

> 
> On Tue, Jul 25, 2017 at 12:17 AM, Jonas Ådahl <jadahl at gmail.com> wrote:
> 
> > On Fri, Jul 21, 2017 at 05:21:38PM +0200, Quentin Glidic wrote:
> > > On 7/20/17 4:33 PM, Matt Hoosier wrote:
> > > > It's useful for the shell implementation to know when these change,
> > > > for example to relay the information on to taskbars or similar.
> > >
> > > The idea is good, we need something like that. (But maybe not, see
> > below).
> > >
> > >
> > > > To avoid ABI changes or the need to make the weston_desktop_surface
> > > > definition public, new functions are introduced for attaching
> > > > listeners to these signals.
> > >
> > > We don’t care that much about ABI changes, but you’re right that I do
> > care
> > > about the struct staying private.
> > >
> > >
> > > > Signed-off-by: Matt Hoosier <matt.hoosier at gmail.com>
> > > > ---
> > > >   libweston-desktop/libweston-desktop.h |  6 ++++++
> > > >   libweston-desktop/surface.c           | 21 +++++++++++++++++++++
> > > >   2 files changed, 27 insertions(+)
> > > >
> > > > diff --git a/libweston-desktop/libweston-desktop.h
> > b/libweston-desktop/libweston-desktop.h
> > > > index 03b04c7..e38257e 100644
> > > > --- a/libweston-desktop/libweston-desktop.h
> > > > +++ b/libweston-desktop/libweston-desktop.h
> > > > @@ -164,6 +164,12 @@ weston_desktop_surface_set_size(struct
> > weston_desktop_surface *surface,
> > > >                             int32_t width, int32_t height);
> > > >   void
> > > >   weston_desktop_surface_close(struct weston_desktop_surface
> > *surface);
> > > > +void
> > > > +weston_desktop_surface_add_title_listener(struct
> > weston_desktop_surface *surface,
> > > > +                                     struct wl_listener *listener);
> > > > +void
> > > > +weston_desktop_surface_add_app_id_listener(struct
> > weston_desktop_surface *surface,
> > > > +                                      struct wl_listener *listener);
> > > >   void *
> > > >   weston_desktop_surface_get_user_data(struct weston_desktop_surface
> > *surface);
> > > > diff --git a/libweston-desktop/surface.c b/libweston-desktop/surface.c
> > > > index d3be936..97a455c 100644
> > > > --- a/libweston-desktop/surface.c
> > > > +++ b/libweston-desktop/surface.c
> > > > @@ -64,6 +64,8 @@ struct weston_desktop_surface {
> > > >             char *title;
> > > >             char *app_id;
> > > >             pid_t pid;
> > > > +           struct wl_signal title_signal;
> > > > +           struct wl_signal app_id_signal;
> > > >     };
> > > >     struct {
> > > >             struct weston_desktop_surface *parent;
> > > > @@ -287,6 +289,9 @@ weston_desktop_surface_create(struct
> > weston_desktop *desktop,
> > > >     wl_list_init(&surface->view_list);
> > > >     wl_list_init(&surface->grab_link);
> > > > +   wl_signal_init(&surface->title_signal);
> > > > +   wl_signal_init(&surface->app_id_signal);
> > > > +
> > > >     return surface;
> > > >   }
> > > > @@ -511,6 +516,20 @@ weston_desktop_surface_close(struct
> > weston_desktop_surface *surface)
> > > >
> > surface->implementation_data);
> > > >   }
> > > > +WL_EXPORT void
> > > > +weston_desktop_surface_add_title_listener(struct
> > weston_desktop_surface *surface,
> > > > +                                     struct wl_listener *listener)
> > > > +{
> > > > +   wl_signal_add(&surface->title_signal, listener);
> > > > +}
> > > > +
> > > > +WL_EXPORT void
> > > > +weston_desktop_surface_add_app_id_listener(struct
> > weston_desktop_surface *surface,
> > > > +                                      struct wl_listener *listener)
> > > > +{
> > > > +   wl_signal_add(&surface->app_id_signal, listener);
> > > > +}
> > > > +
> > > >   struct weston_desktop_surface *
> > > >   weston_desktop_surface_from_client_link(struct wl_list *link)
> > > >   {
> > > > @@ -687,6 +706,7 @@ weston_desktop_surface_set_title(struct
> > weston_desktop_surface *surface,
> > > >     free(surface->title);
> > > >     surface->title = tmp;
> > > > +   wl_signal_emit(&surface->title_signal, surface->title);
> > >
> > > I would rather pass the surface as the signal data. Just in case we have
> > in
> > > the future a value that doesn’t fit in a pointer. And calling a getter is
> > > not that bad.
> > >
> > > Also, I prefer to have one signal only, it would reduce the API size (and
> > > avoid it growing too much in the future, since it could work in this
> > case).
> > > We can move the free() to keep both pointer around until after the signal
> > > fired, and a simple pointer comparison will work (if you stored the
> > "const
> > > char *" directly, which you should as with the signal, we guarantee it
> > will
> > > exist until destroy or signal).
> > >
> > >
> > > But it raised a question : Jonas, are set_title() and set_app_id()
> > supposed
> > > to be active without a commit()?
> >
> > No. As per specification they are not tied to wl_surface.commit(). I
> > suppose it is something we can change though, while we can, if it makes
> > any sense. Opinions?
> >
> >
> > Jonas
> >