[libcamera-devel] [PATCH v2 15/27] gst: libcamerasrc: Implement minimal caps negotiation

[Nicolas Dufresne]

This is not expected to work in every possible cases, but should be sufficient as
an initial implementation. What is does is that it turns the StreamFormats into
caps and queries 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 trust the order
in StreamFormats as being sorted best first, but this is not currently in
libcamera. A todo has been added in the head of this file as a reminder to fix
that in the core.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
---
 src/gstreamer/gstlibcamerasrc.cpp | 82 ++++++++++++++++++++++++++++++-
 1 file changed, 81 insertions(+), 1 deletion(-)

diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
index e2c63d1..2c5c34c 100644
--- a/src/gstreamer/gstlibcamerasrc.cpp
+++ b/src/gstreamer/gstlibcamerasrc.cpp
@@ -6,6 +6,12 @@
  * gstlibcamerasrc.cpp - GStreamer Capture Element
  */
 
+/**
+ * \todo libcamera UVC drivers picks the lowest possible resolution first, this
+ * should be fixed so that we get a decent resolution and framerate for the
+ * role by default.
+ */
+
 #include "gstlibcamera-utils.h"
 #include "gstlibcamerapad.h"
 #include "gstlibcamerasrc.h"
@@ -23,6 +29,7 @@ GST_DEBUG_CATEGORY_STATIC(source_debug);
 struct GstLibcameraSrcState {
 	std::unique_ptr<CameraManager> cm;
 	std::shared_ptr<Camera> cam;
+	std::unique_ptr<CameraConfiguration> config;
 	std::vector<GstPad *> srcpads;
 };
 
@@ -131,16 +138,89 @@ gst_libcamera_src_task_enter(GstTask *task, GThread *thread, gpointer user_data)
 	GstLibcameraSrc *self = GST_LIBCAMERA_SRC(user_data);
 	GLibRecLocker(&self->stream_lock);
 	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 */
+		/* 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);
+	/* \todo Check if camera may increase or decrease the number of streams
+	 * regardless of the number of 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);
+
+		/* Retrieve 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 the 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;
+		}
+	}
+
+	{
+		gint 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:
+		GST_ELEMENT_FLOW_ERROR(self, flow_ret);
+		gst_task_stop(task);
+		return;
+	default:
+		break;
 	}
 }
 
-- 
2.24.1