Non-standard device event input for GTK - c

Question

I am using GTK as the user interface to a piece of hardware (a 3D printer). The hardware can create events as a result of user interactions with the machine (not the GUI). For example, they can remove the build plate which trips a switch thus sending a signal to my program that this has happened, but how do I get gtk_main() to recognize that this event has happened?
In other words, how do I get gtk_main() to watch for non-standard device input events?

Answer 1

You can use custom actions provided by GtkApplication.
In any case you must implement by yourself the monitoring code, either by polling your hardware status or by leveraging more advanced techniques (if possible).
/* gcc -o monitor monitor.c $(pkg-config --cflags --libs gtk+-3.0) */
#include <gtk/gtk.h>
static void
startup(GtkApplication *application)
{
GAction *action;
/* plate-removed is a custom action */
action = G_ACTION(g_simple_action_new("plate-removed", NULL));
g_action_map_add_action(G_ACTION_MAP(application), action);
g_object_unref(action);
/* You can connect your callbacks to the GAction::activate signal */
action = g_action_map_lookup_action(G_ACTION_MAP(application), "plate-removed");
g_signal_connect_swapped(action, "activate",
G_CALLBACK(g_print), "Plate has been removed\n");
}
static gpointer
worker_thread(gpointer user_data)
{
GApplication *application = G_APPLICATION(user_data);
for (;;) {
g_usleep(g_random_int_range(500000, 5000000));
/* Event occurred: emit the signal */
g_action_group_activate_action(G_ACTION_GROUP(application),
"plate-removed", NULL);
}
return NULL;
}
static gboolean
polling_loop(gpointer user_data)
{
GApplication *application = G_APPLICATION(user_data);
if (g_random_int_range(1, 20) == 8) {
/* Event occurred: emit the signal */
g_action_group_activate_action(G_ACTION_GROUP(application),
"plate-removed", NULL);
}
return G_SOURCE_CONTINUE;
}
static void
activate(GtkApplication *application)
{
GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_application_add_window(application, GTK_WINDOW(window));
gtk_widget_show_all(window);
/* You can use whatever you want to monitor your hardware, in particular
* a polling loop or a worker thread */
g_timeout_add(50, polling_loop, application);
/* g_thread_new("WorkerThread", worker_thread, application); */
}
int
main(int argc, char *argv[])
{
GtkApplication *application;
int retval;
application = gtk_application_new(NULL, G_APPLICATION_FLAGS_NONE);
g_signal_connect(application, "startup", G_CALLBACK(startup), NULL);
g_signal_connect(application, "activate", G_CALLBACK(activate), NULL);
retval = g_application_run(G_APPLICATION(application), argc, argv);
g_object_unref(application);
return retval;
}