gtk4: Clean up Python example

It's not more or less equivalent to the Rust example.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1573>

video/gtk4/examples/gtksink.py

@@ -1,57 +1,107 @@
 import gi
 import sys
 
-gi.require_version("Gtk", "4.0")
-gi.require_version('Gst', '1.0')
 
+gi.require_version('GLib', '2.0')
+from gi.repository import GLib
+gi.require_version('Gtk', '4.0')
 from gi.repository import Gtk
+gi.require_version('Gst', '1.0')
 from gi.repository import Gst
 
-Gst.init(sys.argv[1:])
-
-gtksink = Gst.ElementFactory.make("gtk4paintablesink", "sink")
-# Get the paintable from the sink
-paintable = gtksink.props.paintable
-
-# Use GL if available
-if paintable.props.gl_context:
-    print("Using GL")
-    source = Gst.ElementFactory.make("gltestsrc", "source")
-    glsink = Gst.ElementFactory.make("glsinkbin", "sink")
-    glsink.props.sink = gtksink
-    sink = glsink
-else:
-    source = Gst.ElementFactory.make("videotestsrc", "source")
-    sink = gtksink
-
-pipeline = Gst.Pipeline.new()
-
-if not pipeline or not source or not sink:
-    print("Not all elements could be created.")
-    exit(-1)
-
-pipeline.add(source)
-pipeline.add(sink)
-source.link(sink)
-
 def on_activate(app):
-    win = Gtk.ApplicationWindow(application=app)
-    box = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
+    pipeline = Gst.Pipeline.new()
+
+    overlay = Gst.ElementFactory.make('clockoverlay', None)
+    overlay.set_property('font-desc', 'Monospace 42')
+
+    gtksink = Gst.ElementFactory.make('gtk4paintablesink', None)
+    paintable = gtksink.get_property('paintable')
+
+    if paintable.props.gl_context:
+        print('Using GL')
+        src = Gst.ElementFactory.make('gltestsrc', None)
+
+        sink = Gst.ElementFactory.make('glsinkbin', None)
+        sink.set_property('sink', gtksink)
+    else:
+        print('Not using GL')
+        src = Gst.ElementFactory.make('videotestsrc', None)
+
+        sink = Gst.Bin.new()
+        convert = Gst.ElementFactory.make('videoconvert', None)
+
+        sink.add(convert)
+        sink.add(gtksink)
+        convert.link(gtksink)
+
+        sink.add_pad(Gst.GhostPad.new('sink', gtksink.get_static_pad('sink')))
+
+    pipeline.add(src)
+    pipeline.add(overlay)
+    pipeline.add(sink)
+
+    src.link_filtered(overlay, Gst.Caps.from_string('video/x-raw(ANY), width=640, height=480'))
+    overlay.link(sink)
+
+    window = Gtk.ApplicationWindow(application=app)
+    window.set_default_size(640, 480)
+
+    vbox = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
 
     picture = Gtk.Picture.new()
-    picture.set_size_request(640, 480)
-    # Set the paintable on the picture
     picture.set_paintable(paintable)
-    box.append(picture)
 
-    btn = Gtk.Button(label="▶/⏸")
-    box.append(btn)
-    btn.connect('clicked', lambda _: pipeline.set_state(Gst.State.PAUSED) if pipeline.get_state(1)[1]==Gst.State.PLAYING else pipeline.set_state(Gst.State.PLAYING))
+    vbox.append(picture)
 
-    win.set_child(box)
-    win.present()
+    label = Gtk.Label.new('Position: 00:00:00')
+    vbox.append(label)
 
-app = Gtk.Application()
-app.connect('activate', on_activate)
+    window.set_child(vbox)
+    window.present()
 
-app.run(None)
+    app.add_window(window)
+
+    def on_timeout():
+        (res, position) = pipeline.query_position(Gst.Format.TIME)
+        if not res or position == -1:
+            label.set_text('Position: 00:00:00')
+        else:
+            seconds = int(position / 1000000000)
+            minutes = int(seconds / 60)
+            hours = int(minutes / 60)
+            seconds = seconds % 60
+            minutes = minutes % 60
+            label.set_text(f'Position: {hours:02}:{minutes:02}:{seconds:02}')
+
+        return True
+
+    GLib.timeout_add(500, on_timeout)
+
+    pipeline.set_state(Gst.State.PLAYING)
+
+    def on_bus_msg(_, msg):
+        match msg.type:
+            case Gst.MessageType.EOS:
+                app.quit()
+            case Gst.MessageType.ERROR:
+                (err, _) = msg.parse_error()
+                print(f'Error from {msg.src.path_string()}: {err}')
+                app.quit()
+
+        return True
+
+    bus = pipeline.get_bus()
+    bus.add_watch(GLib.PRIORITY_DEFAULT, on_bus_msg)
+
+    def on_close(_):
+        window.close()
+        pipeline.set_state(Gst.State.NULL)
+    app.connect('shutdown', on_close)
+
+if __name__ == '__main__':
+    Gst.init(None)
+    app = Gtk.Application()
+    app.connect('activate', on_activate)
+    res = app.run(None)
+    sys.exit(res)