[libcamera-devel] [PATCH v1 15/23] gst: libcamerasrc: Implement minimal caps negotiation

[Nicolas Dufresne]

Le mercredi 12 février 2020 à 01:47 +0200, Laurent Pinchart a écrit :
> Hi Nicolas,
> 
> Thank you for the patch.
> 
> On Tue, Jan 28, 2020 at 10:32:02PM -0500, Nicolas Dufresne wrote:
> > From: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> > 
> > This is not expected to work in every possible cases, but should be sufficient as
> > an initial implementation. What is does it that it turns the StreamFormats into
> 
> s/is does it/it does is/
> 
> > caps and query downstream caps with that as a filter.
> 
> s/query/queries/
> 
> > The result is the subset of caps that can be used. We then keep the first
> > structure in that result and fixate using the default values found in
> > StreamConfiguration as a default in case a range is available.
> > 
> > We then validate this configuration and turn the potentially modified
> > configuration into caps that we push downstream. Note that we strust the order
> 
> s/strust/trust/
> 
> > in StreamFormats as being sorted best first, but this is not currently in
> > libcamera.
> 
> Could you add a \todo comment in the code to address this ?
> 
> > Signed-off-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> > ---
> >  src/gstreamer/gstlibcamerasrc.cpp | 71 +++++++++++++++++++++++++++++++
> >  1 file changed, 71 insertions(+)
> > 
> > diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
> > index b1a21dc..7b478fa 100644
> > --- a/src/gstreamer/gstlibcamerasrc.cpp
> > +++ b/src/gstreamer/gstlibcamerasrc.cpp
> > @@ -24,6 +24,7 @@ GST_DEBUG_CATEGORY_STATIC(source_debug);
> >  struct GstLibcameraSrcState {
> >  	std::shared_ptr<CameraManager> cm;
> >  	std::shared_ptr<Camera> cam;
> > +	std::unique_ptr<CameraConfiguration> config;
> >  	std::vector<GstPad *> srcpads;
> >  };
> >  
> > @@ -132,16 +133,86 @@ gst_libcamera_src_task_enter(GstTask *task, GThread *thread, gpointer user_data)
> >  	STREAM_LOCKER(user_data);
> >  	GstLibcameraSrc *self = GST_LIBCAMERA_SRC(user_data);
> >  	GstLibcameraSrcState *state = self->state;
> > +	GstFlowReturn flow_ret = GST_FLOW_OK;
> >  
> >  	GST_DEBUG_OBJECT(self, "Streaming thread has started");
> >  
> >  	guint group_id = gst_util_group_id_next();
> > +	StreamRoles roles;
> >  	for (GstPad *srcpad : state->srcpads) {
> >  		/* Create stream-id and push stream-start */
> >  		g_autofree gchar *stream_id = gst_pad_create_stream_id(srcpad, GST_ELEMENT(self), nullptr);
> >  		GstEvent *event = gst_event_new_stream_start(stream_id);
> >  		gst_event_set_group_id(event, group_id);
> >  		gst_pad_push_event(srcpad, event);
> > +
> > +		/* Collect the streams roles for the next iteration */
> > +		roles.push_back(gst_libcamera_pad_get_role(srcpad));
> > +	}
> > +
> > +	/* Generate the stream configurations, there should be one per pad */
> > +	state->config = state->cam->generateConfiguration(roles);
> > +	g_assert(state->config->size() == state->srcpads.size());
> 
> What if more pads have been created than the camera can handle ? Is
> there a way to fail more gracefully than with a g_assert() ? It doesn't
> have to be implement now, but would be nice in the future. Maybe a \todo
> comment with a brief description of how to fix it ?

Should add a \todo, I didn't remember this. In fact, I should check if
the size is the same and fail otherwise, there is nothing I can do
about this. User wanted N stream, and this is not possible.

I don't think there is any clean way to do it right now. Normally I
should reject the pad request, but at that moment, I have no
information about frame size, or anything.

Note that there is no such thing as multiple pads at the moment, that's
not implemented yet. I just wanted to have relatively generic code to
avoid the follow up looking like a rewrite.

> 
> > +
> > +	for (gsize i = 0; i < state->srcpads.size(); i++) {
> > +		GstPad *srcpad = state->srcpads[i];
> > +		StreamConfiguration &stream_cfg = state->config->at(i);
> > +
> > +		/* Retreive the supported caps */
> 
> s/Retreive/Retrieve/
> 
> > +		g_autoptr(GstCaps) filter = gst_libcamera_stream_formats_to_caps(stream_cfg.formats());
> > +		g_autoptr(GstCaps) caps = gst_pad_peer_query_caps(srcpad, filter);
> > +		if (gst_caps_is_empty(caps)) {
> > +			flow_ret = GST_FLOW_NOT_NEGOTIATED;
> > +			break;
> > +		}
> > +
> > +		/* Fixate caps and configure the stream */
> > +		caps = gst_caps_make_writable(caps);
> > +		gst_libcamera_configure_stream_from_caps(stream_cfg, caps);
> > +	}
> > +
> > +	if (flow_ret != GST_FLOW_OK)
> > +		goto done;
> > +
> > +	/* Validate the configuration */
> > +	if (state->config->validate() == CameraConfiguration::Invalid) {
> > +		flow_ret = GST_FLOW_NOT_NEGOTIATED;
> > +		goto done;
> > +	}
> > +
> > +	/* Regardless if it has been modified, create clean caps and push the
> > +	 * caps event, downstream will decide if hte caps are acceptable */
> 
> s/hte/the/
> 
> Comment style:
> 
> 	/*
> 	 * ...
> 	 */
> 
> > +	for (gsize i = 0; i < state->srcpads.size(); i++) {
> > +		GstPad *srcpad = state->srcpads[i];
> > +		const StreamConfiguration &stream_cfg = state->config->at(i);
> > +
> > +		g_autoptr(GstCaps) caps = gst_libcamera_stream_configuration_to_caps(stream_cfg);
> > +		if (!gst_pad_push_event(srcpad, gst_event_new_caps(caps))) {
> > +			flow_ret = GST_FLOW_NOT_NEGOTIATED;
> > +			break;
> > +		}
> > +	}
> > +
> > +	ret = state->cam->configure(state->config.get());
> > +	if (ret) {
> > +		GST_ELEMENT_ERROR(self, RESOURCE, SETTINGS,
> > +				  ("Failed to configure camera: %s", g_strerror(-ret)),
> > +				  ("Camera.configure() failed with error code %i", ret));
> 
> s/.configure/::configure/
> 
> > +		gst_task_stop(task);
> > +		return;
> 
> Just for my information, why is there no need to push an EOS events on
> pads here ? And what if the previous loop fails and sets flow_ret to
> GST_FLOW_NOT_NEGOTIATED and this then fails, is it expected that the
> done: label won't be reached in that case ?
> 
> > +	}
> > +
> > +done:
> > +	switch (flow_ret) {
> > +	case GST_FLOW_NOT_NEGOTIATED:
> > +		for (GstPad *srcpad : state->srcpads) {
> > +			gst_pad_push_event(srcpad, gst_event_new_eos());
> > +		}
> 
> No need for braces.
> 
> > +		GST_ELEMENT_FLOW_ERROR(self, flow_ret);
> > +		gst_task_stop(task);
> > +		return;
> > +	default:
> > +		break;
> >  	}
> >  }
> >