Re: gstmm add element to pipeline test

[José Alburquerque <jaalburquerque cox net>]

Murray Cumming wrote:
> On Tue, 2007-12-04 at 12:38 -0500, José Alburquerque wrote:
> [snip]
> The gst_bus_add_signal_watch() call sort of 
>   
> > "enables" the "message" signal of  Gst::Bus 
> > (see gst_bus_add_signal_watch 
> > <http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstBus.html#gst-bus-add-signal-watch>) 
> > (I'll add a comment as you say).  Without the call, the "message" signal 
> > of the bus is never emitted so this call is necessary (I guess).
> >     
> [snip]
>
> Why is this not the default for GstPipeline in C? Why would we make it the default in C++?
>
> [snip]
>   

I see what you're saying.  By default, it looks like the message signal 
is not emitted in C.  The reason I thought we would needed in C++ is the 
following:  The C code for getting messages from a GstBus appears below 
(taken from GADM 10 
<http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/chapter-helloworld.html>):

 bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
 gst_bus_add_watch (bus, bus_call, loop);
 gst_object_unref (bus);

As you can see gst_add_watch 
<http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstBus.html#gst-bus-add-watch>() 
takes a GstBus*, a GstBusFunc 
<http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstBus.html#GstBusFunc> 
(a function pointer) and additional data.  As the main loop executes, 
when a message is received on the bus, the GstBusFunc (in this case 
bus_call) is called in this way.  My question would be:  How would we do 
this in C++?  I'm pretty new to gstreamer and wrapping so I'm sure 
missing something, but this is why I thought that it might be necessary 
to enable the "message" signal for C++.  This way, the parallel C++ code 
for the above would like like:

 RefPtr<Bus> bus = pipeline->get_bus();
 bus->signal_message().connect(sigc::bind< RefPtr<MainLoop> >(
   sigc::ptr_fun(&bus_message_received), mainLoop) );


At any rate, I'm sure you might have better suggestions. :-)  Thanks.

-Jose