Add GStreamer plugin and element skeleton

This implements the GStreamer plugin interface and adds libcamerasrc
element feature to it. This is just enough to allow plugin
introspection.

gst-inspect-1.0 build/src/gstreamer/libgstlibcamera.so
Plugin Details:
  Name                     libcamera
  Description              libcamera capture plugin
  Filename                 build/src/gstreamer/libgstlibcamera.so
  Version                  0.0.0+1042-6c9f16d3-dirty
  License                  LGPL
  Source module            libcamera
  Binary package           libcamera
  Origin URL               https://libcamera.org

  libcamerasrc: libcamera Source

  1 features:

GST_PLUGIN_PATH=$(pwd)/build/src/gstreamer gst-inspect-1.0 libcamerasrc
Factory Details:
  Rank                     primary (256)
  Long-name                libcamera Source
  Klass                    Source/Video
  Description              Linux Camera source using libcamera
  Author                   Nicolas Dufresne <nicolas.dufresne@collabora.com

Plugin Details:
  Name                     libcamera
  Description              libcamera capture plugin
  Filename                 /home/nicolas/Sources/libcamera/build/src/gstreamer/libgstlibcamera.so
  Version                  0.0.0+1042-6c9f16d3-dirty
  License                  LGPL
  Source module            libcamera
  Binary package           libcamera
  Origin URL               https://libcamera.org

GObject
 +----GInitiallyUnowned
       +----GstObject
             +----GstElement
                   +----GstLibcameraSrc

Pad Templates:
  none

Element has no clocking capabilities.
Element has no URI handling capabilities.

Pads:
  none

Element Properties:
  name                : The name of the object
                        flags: accès en lecture, accès en écriture, 0x2000
                        String. Default: "libcamerasrc0"
  parent              : The parent of the object
                        flags: accès en lecture, accès en écriture, 0x2000
                        Object of type "GstObject"

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
[Silence -Wunused-function warning for older GLib versions]
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

meson_options.txt

@@ -7,6 +7,11 @@ option('documentation',
         type : 'boolean',
         description : 'Generate the project documentation')
 
+option('gstreamer',
+        type : 'feature',
+        value : 'auto',
+        description : 'Compile libcamera GStreamer plugin')
+
 option('test',
         type : 'boolean',
         description: 'Compile and include the tests')

src/gstreamer/gstlibcamera.c

@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Collabora Ltd.
+ *     Author: Nicolas Dufresne <nicolas.dufresne@collabora.com>
+ *
+ * gstlibcamera.c - GStreamer plugin
+ */
+
+#include "gstlibcamerasrc.h"
+
+static gboolean
+plugin_init(GstPlugin *plugin)
+{
+	return gst_element_register(plugin, "libcamerasrc", GST_RANK_PRIMARY,
+				    GST_TYPE_LIBCAMERA_SRC);
+	return TRUE;
+}
+
+GST_PLUGIN_DEFINE(GST_VERSION_MAJOR, GST_VERSION_MINOR,
+		  libcamera, "libcamera capture plugin",
+		  plugin_init, VERSION, "LGPL", PACKAGE, "https://libcamera.org");

src/gstreamer/gstlibcamerasrc.cpp

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Collabora Ltd.
+ *     Author: Nicolas Dufresne <nicolas.dufresne@collabora.com>
+ *
+ * gstlibcamerasrc.cpp - GStreamer Capture Element
+ */
+
+#include "gstlibcamerasrc.h"
+
+struct _GstLibcameraSrc {
+	GstElement parent;
+};
+
+G_DEFINE_TYPE(GstLibcameraSrc, gst_libcamera_src, GST_TYPE_ELEMENT);
+
+static void
+gst_libcamera_src_init(GstLibcameraSrc *self)
+{
+}
+
+static void
+gst_libcamera_src_class_init(GstLibcameraSrcClass *klass)
+{
+	GstElementClass *element_class = (GstElementClass *)klass;
+
+	gst_element_class_set_metadata(element_class,
+				       "libcamera Source", "Source/Video",
+				       "Linux Camera source using libcamera",
+				       "Nicolas Dufresne <nicolas.dufresne@collabora.com");
+}

src/gstreamer/gstlibcamerasrc.h

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Collabora Ltd.
+ *     Author: Nicolas Dufresne <nicolas.dufresne@collabora.com>
+ *
+ * gstlibcamerasrc.h - GStreamer Capture Element
+ */
+
+#ifndef __GST_LIBCAMERA_SRC_H__
+#define __GST_LIBCAMERA_SRC_H__
+
+#include <gst/gst.h>
+
+G_BEGIN_DECLS
+
+#define GST_TYPE_LIBCAMERA_SRC gst_libcamera_src_get_type()
+G_DECLARE_FINAL_TYPE(GstLibcameraSrc, gst_libcamera_src,
+		     GST_LIBCAMERA, SRC, GstElement)
+
+G_END_DECLS
+
+#endif /* __GST_LIBCAMERA_SRC_H__ */

src/gstreamer/meson.build

@@ -0,0 +1,32 @@
+libcamera_gst_sources = [
+    'gstlibcamera.c',
+    'gstlibcamerasrc.cpp',
+]
+
+libcamera_gst_c_args = [
+    '-DVERSION="@0@"'.format(libcamera_git_version),
+    '-DPACKAGE="@0@"'.format(meson.project_name()),
+]
+
+glib_dep = dependency('glib', required : get_option('gstreamer'))
+
+gst_dep = dependency('gstreamer-video-1.0', version : '>=1.14.0',
+                     required : get_option('gstreamer'))
+
+if glib_dep.found() and gst_dep.found()
+    # The G_DECLARE_FINAL_TYPE macro creates static inline functions that were
+    # not marked as possibly unused prior to GLib v2.63.0. This causes clang to
+    # complain about the ones we are not using. Silence the -Wunused-function
+    # warning in that case.
+    if cc.get_id() == 'clang' and glib_dep.version().version_compare('<2.63.0')
+        libcamera_gst_c_args += [ '-Wno-unused-function' ]
+    endif
+
+    libcamera_gst = shared_library('gstlibcamera',
+        libcamera_gst_sources,
+        c_args : libcamera_gst_c_args,
+        dependencies : [libcamera_dep, gst_dep],
+        install: true,
+        install_dir : '@0@/gstreamer-1.0'.format(get_option('libdir')),
+    )
+endif

src/meson.build

@@ -10,3 +10,5 @@ subdir('qcam')
 if get_option('v4l2')
     subdir('v4l2')
 endif
+
+subdir('gstreamer')