examples: v4l2: Add v4l2src crop example

Add a simple utility to illustrate how to set input cropping on v4l2src.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1089>

subprojects/gst-plugins-good/tests/examples/v4l2/meson.build

@@ -9,3 +9,9 @@ executable('v4l2src-renegotiate', 'v4l2src-renegotiate.c',
   c_args : gst_plugins_good_args,
   include_directories : [configinc],
   install: false)
+
+executable('v4l2src-crop', 'v4l2src-crop.c',
+  dependencies: [gst_dep],
+  c_args : gst_plugins_good_args,
+  include_directories : [configinc],
+  install: false)

subprojects/gst-plugins-good/tests/examples/v4l2/v4l2src-crop.c

@@ -0,0 +1,213 @@
+/* GStreamer
+ * Copyright (C) 2021 Damian Hobson-Garcia <dhobsong@igel.co.jp>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+/* demo application showing v4l2src cropping */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gst/gst.h>
+
+#define PLAY_TIME_SEC   5
+
+struct rect
+{
+  guint left;
+  guint top;
+  guint width;
+  guint height;
+};
+
+static gboolean
+bus_call (GstBus * bus, GstMessage * msg, gpointer data)
+{
+  GMainLoop *loop = (GMainLoop *) data;
+
+  switch (GST_MESSAGE_TYPE (msg)) {
+
+    case GST_MESSAGE_EOS:
+      g_print ("End of stream\n");
+      g_main_loop_quit (loop);
+      break;
+
+    case GST_MESSAGE_ERROR:{
+      gchar *debug;
+      GError *error;
+
+      gst_message_parse_error (msg, &error, &debug);
+      g_free (debug);
+
+      g_printerr ("Error: %s\n", error->message);
+      g_error_free (error);
+
+      g_main_loop_quit (loop);
+      break;
+    }
+    default:
+      break;
+  }
+
+  return TRUE;
+}
+
+static void
+on_crop_bounds (GstElement * element, GParamSpec * pspec, void *data)
+{
+  GValue bounds = { 0 };
+  int i;
+  union
+  {
+    struct rect rect;
+    guint vals[4];
+  } crop_bounds;
+
+  struct rect crop;
+
+  g_value_init (&bounds, G_PARAM_SPEC_VALUE_TYPE (pspec));
+  g_object_get_property (G_OBJECT (element), "crop-bounds", &bounds);
+
+  if (gst_value_array_get_size (&bounds) != 4) {
+    g_error ("Invalid crop bounds received");
+    return;
+  }
+
+  for (i = 0; i < 4; i++) {
+    const GValue *val = gst_value_array_get_value (&bounds, i);
+    if (!G_VALUE_HOLDS_INT (val)) {
+      g_error ("Invalid crop bounds value received");
+      return;
+    }
+    crop_bounds.vals[i] = g_value_get_int (val);
+  }
+
+  g_print ("Crop bounds: @(%d, %d), %dx%d\n", crop_bounds.rect.left,
+      crop_bounds.rect.top, crop_bounds.rect.width, crop_bounds.rect.height);
+
+  /* Crop out a region from the bottom right quandrant of the
+   * crop bounding region */
+  crop.left = (crop_bounds.rect.width - crop_bounds.rect.left) / 2;
+  crop.top = (crop_bounds.rect.height - crop_bounds.rect.top) / 2;
+  crop.width = crop.left / 2;
+  crop.height = crop.left / 2;
+
+  g_print ("Setting crop region to @(%d, %d), %dx%d\n", crop.left, crop.top,
+      crop.width, crop.height);
+
+  g_object_set (G_OBJECT (element),
+      "crop-left", crop.left,
+      "crop-top", crop.top,
+      "crop-right", crop_bounds.rect.width - crop.left - crop.width,
+      "crop-bottom", crop_bounds.rect.height - crop.top - crop.height, NULL);
+}
+
+static const gchar *device = "/dev/video0";
+static const gchar *videosink = "autovideosink";
+
+static GOptionEntry entries[] = {
+  {"device", 'd', 0, G_OPTION_ARG_STRING, &device, "V4L2 Camera Device",
+      NULL},
+  {"videosink", 's', 0, G_OPTION_ARG_STRING, &videosink, "Video Sink to use",
+      NULL},
+  {NULL}
+};
+
+static gboolean
+send_eos (gpointer user_data)
+{
+  GstElement *pipeline = user_data;
+
+  gst_element_send_event (pipeline, gst_event_new_eos ());
+  return FALSE;
+}
+
+int
+main (int argc, char *argv[])
+{
+  GMainLoop *loop;
+
+  GstElement *pipeline, *source, *conv, *sink;
+  GstBus *bus;
+  guint bus_watch_id;
+  GError *error = NULL;
+  GOptionContext *context;
+  gboolean ret;
+
+  context = g_option_context_new ("- test v4l2src crop");
+  g_option_context_add_main_entries (context, entries, GETTEXT_PACKAGE);
+  g_option_context_add_group (context, gst_init_get_option_group ());
+  ret = g_option_context_parse (context, &argc, &argv, &error);
+  g_option_context_free (context);
+
+  if (!ret) {
+    g_print ("option parsing failed: %s\n", error->message);
+    g_error_free (error);
+    return 1;
+  }
+
+  gst_init (&argc, &argv);
+
+  loop = g_main_loop_new (NULL, FALSE);
+
+  /* Create gstreamer elements */
+  pipeline = gst_pipeline_new ("v4l2src crop sample");
+  source = gst_element_factory_make ("v4l2src", "source");
+  conv = gst_element_factory_make ("videoconvert", "converter");
+  sink = gst_element_factory_make (videosink, "video-output");
+
+  if (!pipeline || !source || !conv || !sink) {
+    g_printerr ("One or more elements could not be created. Exiting.\n");
+    return -1;
+  }
+
+  /* Set up the v4l2src element */
+  g_object_set (G_OBJECT (source), "device", device, NULL);
+
+  /* Add a message handler */
+  bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
+  bus_watch_id = gst_bus_add_watch (bus, bus_call, loop);
+  gst_object_unref (bus);
+
+  gst_bin_add_many (GST_BIN (pipeline), source, conv, sink, NULL);
+  gst_element_link_many (source, conv, sink, NULL);
+
+  /* Connect a callback to be notified when the crop bounding region is
+   * retreived from the V4L2 device */
+  g_signal_connect (source, "notify::crop-bounds", (GCallback) on_crop_bounds,
+      NULL);
+
+  /* Set the pipeline to "playing" state */
+  gst_element_set_state (pipeline, GST_STATE_PLAYING);
+
+  /* Stop the playback after specified time */
+  g_timeout_add_seconds (PLAY_TIME_SEC, send_eos, pipeline);
+
+  g_main_loop_run (loop);
+
+  /* Out of the main loop, clean up nicely */
+  g_print ("Stopping playback\n");
+  gst_element_set_state (pipeline, GST_STATE_NULL);
+
+  g_print ("Deleting pipeline\n");
+  gst_object_unref (GST_OBJECT (pipeline));
+  g_source_remove (bus_watch_id);
+  g_main_loop_unref (loop);
+
+  return 0;
+}