tools: gst-device-monitor: Print gst-launch example

Print a gst-launch-1.0 line that could get to this device,
useful as we don't have other ways to see what it does exactly.
This may not work if the create element has configurations other than
properties.

https://bugzilla.gnome.org/show_bug.cgi?id=781152

tools/gst-device-monitor.c

@@ -42,6 +42,99 @@ typedef struct
 
 static gboolean bus_msg_handler (GstBus * bus, GstMessage * msg, gpointer data);
 
+static gchar *
+get_launch_line (GstDevice * device)
+{
+  static const char *const ignored_propnames[] =
+      { "name", "parent", "direction", "template", "caps", NULL };
+  GString *launch_line;
+  GstElement *element;
+  GstElement *pureelement;
+  GParamSpec **properties, *property;
+  GValue value = G_VALUE_INIT;
+  GValue pvalue = G_VALUE_INIT;
+  guint i, number_of_properties;
+  GstElementFactory *factory;
+
+  element = gst_device_create_element (device, NULL);
+
+  if (!element)
+    return NULL;
+
+  factory = gst_element_get_factory (element);
+  if (!factory) {
+    gst_object_unref (element);
+    return NULL;
+  }
+
+  if (!gst_plugin_feature_get_name (factory)) {
+    gst_object_unref (element);
+    return NULL;
+  }
+
+  launch_line = g_string_new (gst_plugin_feature_get_name (factory));
+
+  pureelement = gst_element_factory_create (factory, NULL);
+
+  /* get paramspecs and show non-default properties */
+  properties =
+      g_object_class_list_properties (G_OBJECT_GET_CLASS (element),
+      &number_of_properties);
+  if (properties) {
+    for (i = 0; i < number_of_properties; i++) {
+      gint j;
+      gboolean ignore = FALSE;
+      property = properties[i];
+
+      /* skip some properties */
+      if ((property->flags & G_PARAM_READWRITE) != G_PARAM_READWRITE)
+        continue;
+
+      for (j = 0; ignored_propnames[j]; j++)
+        if (!g_strcmp0 (ignored_propnames[j], property->name))
+          ignore = TRUE;
+
+      if (ignore)
+        continue;
+
+      /* Can't use _param_value_defaults () because sub-classes modify the
+       * values already.
+       */
+
+      g_value_init (&value, property->value_type);
+      g_value_init (&pvalue, property->value_type);
+      g_object_get_property (G_OBJECT (element), property->name, &value);
+      g_object_get_property (G_OBJECT (pureelement), property->name, &pvalue);
+      if (gst_value_compare (&value, &pvalue) != GST_VALUE_EQUAL) {
+        gchar *valuestr = gst_value_serialize (&value);
+
+        if (!valuestr) {
+          GST_WARNING ("Could not serialize property %s:%s",
+              GST_OBJECT_NAME (element), property->name);
+          g_free (valuestr);
+          goto next;
+        }
+
+        g_string_append_printf (launch_line, " %s=%s",
+            property->name, valuestr);
+        g_free (valuestr);
+
+      }
+
+    next:
+      g_value_unset (&value);
+      g_value_unset (&pvalue);
+    }
+    g_free (properties);
+  }
+
+  gst_object_unref (element);
+  gst_object_unref (pureelement);
+
+  return g_string_free (launch_line, FALSE);
+}
+
+
 static gboolean
 print_structure_field (GQuark field_id, const GValue * value,
     gpointer user_data)
@@ -97,6 +190,12 @@ device_added (GstDevice * device)
     gst_structure_free (props);
     g_print ("\n");
   }
+  str = get_launch_line (device);
+  if (gst_device_has_classes (device, "Source"))
+    g_print ("\tgst-launch-1.0 %s ! ...\n", str);
+  if (gst_device_has_classes (device, "Sink"))
+    g_print ("\tgst-launch-1.0 ... ! %s\n", str);
+  g_free (str);
   g_print ("\n");
 
   g_free (name);