Get the window handle in PyGI

问题:

In my program I use PyGObject/PyGI and GStreamer to show a video in my GUI. The video is shown in a Gtk.DrawingArea and therefore I need to get it's window-handle in the realize-signal-handler. On Linux I get that handle using:

drawing_area.get_property('window').get_xid()

But how do I get the handle on Windows?

I searched on the internet but found only examples for PyGtk using window.handle which does not work using PyGI.

The GStreamer documentation provides an example which uses the GDK_WINDOW_HWND macro to get the handle. This macro uses AFAIK gdk_win32_drawable_get_handle. But how to do it in Python using PyGI?

Update 15-07-28: Added (simplified) code
I'm still not getting video playback to work on Windows.
Problem 1: I cannot get the window handle in _on_video_realize().
Problem 2: The method _on_player_sync_message() is never called.

class MultimediaPlayer:
    def __init__(self):
        # ... some init stuff ...

        self._drawing_area.connect('realize', self._on_video_realize)
        self._drawing_area.connect('unrealize', self._on_video_unrealize)

        # GStreamer setup
        # ---------------
        self._player = Gst.ElementFactory.make('playbin', 'MultimediaPlayer')
        bus = self._player.get_bus()
        bus.add_signal_watch()
        bus.connect('message', self._on_player_message)
        bus.enable_sync_message_emission()
        bus.connect('sync-message::element', self._on_player_sync_message)

    def _on_video_realize(self, widget):
        print('----------> _on_video_realize')
        # The xid must be retrieved first in GUI-thread and before
        # playing pipeline.
        if sys.platform == "win32":
            self._drawing_area.get_property('window').ensure_native()
            # -------------------------------------------------------------
            # TODO [PROBLEM 1] How to get handle here?
            #                  self._drawing_area.GetHandle() does not exist!
            # -------------------------------------------------------------
        else:
            self._wnd_hnd = (self._drawing_area.get_property('window')
                                                                    .get_xid())

    def _on_video_unrealize(self, widget):
        self._player.set_state(Gst.State.NULL)

    def _on_player_message(self, bus, message):
        # ... handle some messages here ...

    def _on_player_sync_message(self, bus, message):
        # ---------------------------------------------------------------------
        # TODO [PROBLEM 2] This method is never called on Windows after opening
        #                  a video_file! But on Linux it is!
        # ---------------------------------------------------------------------

        print('----------> _on_player_sync_message')
        if message.get_structure() is None:
            return True
        if message.get_structure().get_name() == "prepare-window-handle":
            imagesink = message.src
            imagesink.set_property("force-aspect-ratio", True)
            imagesink.set_window_handle(self._wnd_hnd)

    def play(self):
        self._player.set_state(Gst.State.PLAYING)

    def stop(self):
        self._player.set_state(Gst.State.NULL)

    def set_file(self, file):
        # ... 
        self._player.set_property('uri', "file:///" + file)

回答1:

I finally got it. To address the "window handle"-issue I use the workaround/hack by Marwin Schmitt (see here):

def _on_video_realize(self, widget):
    # The window handle must be retrieved first in GUI-thread and before
    # playing pipeline.
    video_window = self._drawing_area.get_property('window')
    if sys.platform == "win32":
        if not video_window.ensure_native():
            print("Error - video playback requires a native window")
        ctypes.pythonapi.PyCapsule_GetPointer.restype = ctypes.c_void_p
        ctypes.pythonapi.PyCapsule_GetPointer.argtypes = [ctypes.py_object]
        drawingarea_gpointer = ctypes.pythonapi.PyCapsule_GetPointer(video_window.__gpointer__, None)
        gdkdll = ctypes.CDLL ("libgdk-3-0.dll")
        self._video_window_handle = gdkdll.gdk_win32_window_get_handle(drawingarea_gpointer)
    else:
        self._video_window_handle = video_window.get_xid()

But there was also the problem, that the "sync-message"-handler was never called. I found out that not all video sinks support embedded video, see here. For example the d3dvideosink does support embedded video, but I was running Windows in a virtual machine and even though 3D hardware acceleration was activated it probably didn't work. Running the same code on a non-virtualized Windows leads to a callback to the "sync-message"-handler where the previously fetched window-handle can be set:

def _on_player_sync_message(self, bus, message):
    if message.get_structure() is None:
        return
    if not GstVideo.is_video_overlay_prepare_window_handle_message(message):
        return
    imagesink = message.src
    imagesink.set_property("force-aspect-ratio", True)
    imagesink.set_window_handle(self._video_window_handle)

Playback on Windows works fine now.

回答2:

Have you tried:

def OnSyncMessage(self, bus, msg):
    if msg.get_structure() is None:
        return True
    message_name = msg.get_structure().get_name()
    if message_name == 'prepare-window-handle':
        imagesink = msg.src
        imagesink.set_property('force-aspect-ratio', True)
        imagesink.set_window_handle(self.DrawingArea.GetHandle())
    return True