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

[Laurent Pinchart]

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 ?

> +
> +	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;
>  	}
>  }
>  

-- 
Regards,

Laurent Pinchart