gstwaylandsink: "hide" video window when pipeline is stopped

[Nicolas Dufresne]

Le jeudi 23 janvier 2020 à 11:47 +0100, Guillermo Rodriguez Garcia a écrit :
> El mié., 22 ene. 2020 a las 21:47, Nicolas Dufresne
> (<nicolas at ndufresne.ca>) escribió:
> > Le mercredi 22 janvier 2020 à 18:36 +0100, Guillermo Rodriguez Garcia a
> > écrit :
> > > Hello all,
> > > 
> > > I am using gstwaylandsink to render to an application supplied surface
> > > (via the GstVideoOverlay interface). I need to control the position of
> > > the video window, so the application creates a top-level, fully
> > > transparent surface with the same size as the screen, then I use
> > > set_render_rectangle to tell waylandsink where the video should
> > > actually be drawn. This is working fine.
> > > 
> > > My problem is that when the pipeline is stopped (state set to NULL),
> > > the video area is cleared to black, and stays on top of the
> > > controlling application. I would need the video area to be "hidden"
> > > instead (i.e. removed from the composition).
> > > 
> > > The thing is that looking at the code it seems that this (hiding the
> > > window) was actually the intended behaviour. Pipeline state changes
> > > are handled in gst_wayland_sink_change_state [1]. For the PAUSED to
> > > READY transition, the code looks like this:
> > > 
> > >     case GST_STATE_CHANGE_PAUSED_TO_READY:
> > >       gst_buffer_replace (&sink->last_buffer, NULL);
> > >       if (sink->window) {
> > >         if (gst_wl_window_is_toplevel (sink->window)) {
> > >           g_clear_object (&sink->window);
> > >         } else {
> > >           /* remove buffer from surface, show nothing */
> > >           gst_wl_window_render (sink->window, NULL, NULL);
> > >         }
> > >       }
> > > 
> > > In my case, sink->window is not a toplevel, so the 'else' branch runs.
> > > 
> > > gst_wl_window_render does a wl_surface_attach with a NULL buffer +
> > > wl_surface_commit, which should actually "hide" the window. Yet for
> > > some reason this is not what is happening.
> > > 
> > > I am probably missing something; any ideas or hints?
> > 
> > Indeed, I would expect exactly what you want to happen. Which compositor is
> > this?
> 
> I am using Weston in my application but I have checked and I get
> exactly the same behaviour with Mutter...

Had a second thought, you said we do remove the surface on the video subsurface,
did we forgot to do the same on the backplate subsurface ? Remember there is 2
subsurfaces, one is a opaque black plane, that handle the bars when there is
padding due to pixel aspect ration adjustment. Maybe that's the problem ?

> 
> Guillermo
> 
> > > Thank you,
> > > 
> > >  [1]
> > > https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/blob/master/ext/wayland/gstwaylandsink.c#L376
> > > 
> > 
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>