fswin.c

#include <gtk/gtk.h>
#include <glib.h>
#include <glib/gprintf.h>

void map_cb(GtkWidget *widget, gpointer data)
{
    gtk_window_set_keep_above(GTK_WINDOW(widget), TRUE);
    g_print("gtk fullscreen window active\n");
    FILE *fp = fopen("/var/tmp/crfswin.running", "w");
    fclose(fp);
    gdk_window_freeze_updates(widget->window);
}

int main(int argc, char *argv[])
{
    GtkWidget *window;
    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

    gtk_window_set_title(GTK_WINDOW(window), "L:SS_N:screenSaver_ID:crfswin-screensaver_FS:S_FH:S_O:U");
    gtk_window_set_modal(GTK_WINDOW(window), TRUE);
    gtk_window_set_decorated(GTK_WINDOW(window), FALSE);
    gtk_window_set_type_hint(GTK_WINDOW (window), GDK_WINDOW_TYPE_HINT_DIALOG);
    g_signal_connect(GTK_WINDOW(window), "destroy", G_CALLBACK(gtk_main_quit), NULL);
    g_signal_connect(GTK_WINDOW(window), "map-event", G_CALLBACK(map_cb), NULL);
    gtk_window_fullscreen(GTK_WINDOW(window));
    gtk_widget_show(window);
    gtk_window_set_keep_above(GTK_WINDOW(window), TRUE);

    gtk_main();
    return 0;
}