Code for GUI using GTK Windows and BCM2835

/*   You can see this all up and running in void realms on face book at this address
 *   https://www.facebook.com/groups/1400884323467285/
 *   or at https://www.facebook.com/mark.harrington.142892
 *   Alternatively the net-beans project can be downloaded from here at this address
 *   https://github.com/markh2016/GTKBCMGUI.git
 *   File:   main.c
 *   Author: Mark David Harrington
 *
 *  Created on 23 February 2020, 15:53
 *  Add this line to properties-> build -> complier -> additional properties below
 * `pkg-config --cflags gtk+-3.0`
 *  Add this line to properties -> build -> linker -> additional properties  below
 *  pkg-config --libs gtk+-3.0`
 *  Then click apply  then click OK
 *  Now  your ready to compile GTK  windows software for Linux / Unix
 *  You also need to  include  the following to your settings compiler path
 * Project -> Properties -> Catagories -> C Compiler -> Include Directories
   Copy and past list below into that field within netbeans

 *  /usr/include/gtk-3.0;/usr/include/at-spi2-atk;/usr/include/at-spi2-atk/2.0;/usr/include/dbus-1.0;
    /usr/lib/arm-linux-gnueabihf/dbus-1.0/include;/usr/include/gio-unix-2.0;/usr/include/cairo;
    /usr/include/pango-1.0;/usr/include/harfbuzz;/usr/include/fribidi;/usr/include/atk-1.0;/usr/include/pixman-1;
    /usr/include/freetype2;/usr/include/libpng16;/usr/include/gdk-pixbuf-2.0;/usr/include/libmount;
    /usr/include/blkid;/usr/include/uuid;/usr/include/glib-2.0;
    /usr/lib/arm-linux-gnueabihf/glib-2.0/include;/usr/local/lib
 */

/* Program source code below  from here */

#include <stdio.h>
#include <stdlib.h>
#include <gtk/gtk.h>
#include <bcm2835.h>

/*
 * simple gtk application
 *
 */

#define PIN RPI_GPIO_P1_11


/*global variable declaration*/

    GtkWidget *window; /* window */
    GtkWidget *halign; /*Layout of child objects in window container */
    GtkWidget *btn;    /*Button which we will send signals from */
    int gv_count = 0 ;
    char *btofftext = "Switch Off" ;
    char *btontext =  "Switch On " ;


/* this is our event handler for button clicked */
void button_clicked(GtkWidget *widget, gpointer data) {


  if(gv_count > 1)
  {
      gv_count = 0 ;
  }

  g_print("clicked\n");

  if(gv_count == 0){
  bcm2835_gpio_write(PIN, HIGH);
  gtk_button_set_label(GTK_BUTTON(btn),btofftext);
  }


  if(gv_count==1 )
  {
    bcm2835_gpio_write(PIN, LOW);
     gtk_button_set_label(GTK_BUTTON(btn),btontext);
  }

   gv_count+=1 ;

}

/* another callback */
void destroy (GtkWidget *widget, gpointer *data)
{
    bcm2835_close();
    gtk_main_quit ();
}


int main(int argc, char** argv) {



    /* init hardware */

    if (!bcm2835_init())
      return 1;
     // Set the pin to be an output
    bcm2835_gpio_fsel(PIN, BCM2835_GPIO_FSEL_OUTP);



    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
    gtk_window_set_default_size(GTK_WINDOW(window), 200, 100);
    gtk_window_set_title(GTK_WINDOW(window), "RPI LIGHT Switch");
    gtk_container_set_border_width(GTK_CONTAINER(window), 15);


    /* Define container and add button pluc container */
    halign = gtk_alignment_new(0, 0, 0, 0);
    btn = gtk_button_new_with_label(btontext);
    gtk_widget_set_size_request(btn, 70, 30);

    /*Now add objects */

    gtk_container_add(GTK_CONTAINER(halign), btn);
    gtk_container_add(GTK_CONTAINER(window), halign);

   /* Connect signals */

      g_signal_connect(G_OBJECT(btn), "clicked",
      G_CALLBACK(button_clicked), NULL);


      g_signal_connect(window, "destroy",
            G_CALLBACK (destroy), NULL);


    /*show window with components */
    gtk_widget_show_all(window);

    /* This is the message event loop which continuously monitors the  all events dispatched by
     * buttons , any other widgets inside the windows  and window events
     */

    gtk_main();

    return (EXIT_SUCCESS);
}