Add an example sink element and override the chain and event functions of pads

Otherwize we will get 2 time acces to the element in it, which does
not make much sense. The _full variant can still be used.

examples/python/sinkelement.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python
+# -*- Mode: Python -*-
+# vi:si:et:sw=4:sts=4:ts=4
+
+# sinkelement.py
+# (c) 2005 Edward Hervey <edward@fluendo.com>
+# (c) 2007 Jan Schmidt <jan@fluendo.com>
+# Licensed under LGPL
+#
+# Small test application to show how to write a sink element
+# in 20 lines in python and place into the gstreamer registry
+# so it can be autoplugged or used from parse_launch.
+#
+# Run this script with GST_DEBUG=python:5 to see the debug
+# messages
+
+from gi.repository import Gst, GObject
+
+#
+# Simple Sink element created entirely in python
+#
+class MySink(Gst.Element):
+    __gstmetadata__ = ('CustomSink','Sink', \
+                      'Custom test sink element', 'Edward Hervey')
+
+    __gsttemplates__ = Gst.PadTemplate.new ("sinkpadtemplate",
+                                            Gst.PadDirection.SINK,
+                                            Gst.PadPresence.ALWAYS,
+                                            Gst.Caps.new_any())
+
+    def __init__(self):
+        Gst.Element.__init__(self)
+        Gst.info('creating sinkpad')
+        self.sinkpad = Gst.Pad.new_from_template(self.__gsttemplates__, "sink")
+        Gst.info('adding sinkpad to self')
+        self.add_pad(self.sinkpad)
+
+        Gst.info('setting chain/event functions')
+        self.sinkpad.set_chain_function(self.chainfunc)
+        self.sinkpad.set_event_function(self.eventfunc)
+        st = Gst.Structure.from_string("yes,fps=1/2")[0]
+
+    def chainfunc(self, pad, buffer):
+        Gst.info("%s timestamp(buffer):%d" % (pad, buffer.pts))
+        return Gst.FlowReturn.OK
+
+    def eventfunc(self, pad, event):
+        Gst.info("%s event:%r" % (pad, event.type))
+        return True
+
+GObject.type_register(MySink)
+__gstelementfactory__ = ("mysink", Gst.Rank.NONE, MySink)

gi/overrides/Gst.py

@@ -96,6 +96,24 @@ Caps = override(Caps)
 __all__.append('Caps')
 
 class Pad(Gst.Pad):
+    def __init__(self):
+        self._real_chain_func = None
+        self._real_event_func = None
+
+    def _chain_override(self, pad, parent, buf):
+        return self._real_chain_func(pad, buf)
+
+    def _event_override(self, pad, parent, buf):
+        return self._real_event_func(pad, buf)
+
+    def set_chain_function(self, func):
+        self._real_chain_func = func
+        self.set_chain_function_full(self._chain_override, None)
+
+    def set_event_function(self, func):
+        self._real_event_func = func
+        self.set_event_function_full(self._event_override, None)
+
     def query_caps(self, filter=None):
         return Gst.Pad.query_caps(self, filter)