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Bug 321816 - [API] xoverlay API to post prepare-xwindow-id message
[API] xoverlay API to post prepare-xwindow-id message
Product: GStreamer
Classification: Platform
Component: gst-plugins-base
git master
Other Linux
: Normal normal
: 0.9.6
Assigned To: Julien MOUTTE
GStreamer Maintainers
Depends on:
Reported: 2005-11-18 17:59 UTC by Tim-Philipp Müller
Modified: 2005-11-21 20:41 UTC
See Also:
GNOME target: ---
GNOME version: ---

Description Tim-Philipp Müller 2005-11-18 17:59:03 UTC
I'd like to add an gst_x_overlay_prepare_xwindow_id() function to xoverlay that
post an element message called 'prepare-xwindow-id' on the bus. That function
should be called by elements implementing the GstXOverlay interface just before
they start creating their own X Window. This message can be intercepted by the
application via a synchroneous bus message handler and gives the application the
chance to set the xwindow ID "just in time".

A signal would do as well, but a bus message is more convenient because that way
the application doesn't need to find out the instance implementing the interface
before connecting to it.

So xoverlay elements would basically do:

  if (foo->our_window == NULL)
    gst_x_overlay_prepare_xwindow_id (GST_X_OVERLAY (foo));

  if (foo->our_window == NULL)
    ... create own xwindow ...
    ... use set xwindow id ...

The reason this is necessary is that when an application is using gconfvideosink
or autovideosink it has no control over the state of these sink bins once they
are passed to playbin. They might be set to state NULL and back to READY/PLAYING
at any time, creating a new videosink instances, which in turn requires the
application again to set the xwindow ID. It can only do that reliable if it's
informed when it needs to do that, and this seems to be the best way to me.

Of course this can be hacked around in the sink bins somehow or in playbin, but
it still seems desirable to have this message or signal.

Comment 1 Tim-Philipp Müller 2005-11-18 18:02:02 UTC
Erm, just to clarify, the above code assumes of course that foo->our_window is
also created in the GstXOverlay::set_xwindow_id () implementation
Comment 2 Andy Wingo 2005-11-21 18:53:16 UTC
Hi Tim,

I think this looks good, but I don't really know anything. We should get Julien
to comment on this one. I think this counts as an addition, not a change, so we
can do this during the week. Unblocking on 319388.
Comment 3 Tim-Philipp Müller 2005-11-21 19:02:58 UTC
The reason I made it block on bug #319388 is that if we go for a message here we
should probably convert the two other xoverlay signals 'desired-size-change' and
'have-xwindow-id' to bus messages as well (not sure if those are used anywhere

The reason I want bus messages for this is so that the application doesn't need
to keep track of videosink instances, which it would need to do for

Keeping track of instances being created is a bit tedious when you have things
in bins and possibly multiple bin layers. Not that it can't be done, but I don't
see any reason for these things to stay signals either.

Comment 4 Julien MOUTTE 2005-11-21 19:16:55 UTC
So while we are at it let's comment about XOverlay in general. After discussing
about that with Wim with both agreed that desired size should completely get out
of the XOverlay interface, it should only contain :
- set_xwindow_id
- expose
- have_xwindow_id

I agree with you that having to search in a bin for elements supporting the
interface is a bit painfull. So if you think that having a synched message
posted to the bus for the application to have a change to set its window id is
the best way i m all for it.

So let's add :

void (* prepare_xwindow_id) (GstXOverlay *overlay)

and make have_xwindow_id a message to the bus as well.

Will you do that or should i ?
Comment 5 Tim-Philipp Müller 2005-11-21 19:28:22 UTC
Sounds good to me. I'll do it in a few minutes, if you don't mind.
Comment 6 Tim-Philipp Müller 2005-11-21 20:41:50 UTC
Fixed in CVS:

2005-11-21  Tim-Philipp Müller  <tim at centricular dot net>

        * gst-libs/gst/interfaces/xoverlay.c: (gst_x_overlay_base_init),
        (gst_x_overlay_got_xwindow_id), (gst_x_overlay_prepare_xwindow_id):
        * gst-libs/gst/interfaces/xoverlay.h:
          Remove everything having to do with the desired size; add
          gst_x_overlay_prepare_xwindow_id() function; remove the
          'have-xwindow-id' signal and make gst_x_overlay_got_xwindow_id()
          post a message on the bus instead (#321816).

        * sys/ximage/ximagesink.c: (gst_ximagesink_xoverlay_init):
        * sys/xvimage/xvimagesink.c: (gst_xvimagesink_setcaps),
          Remove desired size stuff (#321816).