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

[Nicolas Dufresne]

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
caps and query downstream caps with that as a filter.

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
in StreamFormats as being sorted best first, but this is not currently in
libcamera.

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());
+
+	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 */
+		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 */
+	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));
+		gst_task_stop(task);
+		return;
+	}
+
+done:
+	switch (flow_ret) {
+	case GST_FLOW_NOT_NEGOTIATED:
+		for (GstPad *srcpad : state->srcpads) {
+			gst_pad_push_event(srcpad, gst_event_new_eos());
+		}
+		GST_ELEMENT_FLOW_ERROR(self, flow_ret);
+		gst_task_stop(task);
+		return;
+	default:
+		break;
 	}
 }
 
-- 
2.24.1