Simple Raspberry pi IOT GTK example for touch screens

/*
 * File:   main.c
 * Author: Mark David Harrington
 * code to illustrate how to use the bcm2835 with GTK 3  and Raspberry pi for IOT
 * applications  across ssh with X11 forwarding
 *
 *  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
 ******************************************************************************************
 *  Full code and image at https://github.com/markh2016/GTKSingleRPILightSwitch.git ***** *
 * ****************************************************************************************
 */

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

/*
 * simple gtk application
 * MD Harrington
 */

#define PIN RPI_GPIO_P1_11


/*global variable declaration*/

    GtkWidget *window; /* window */
    GtkWidget *btn;    /*Button which we will send signals from */
    GtkWidget *offimage ;
    GtkWidget *onimage  ;
    int gv_count = 0 ;


/* this is our event handler for button clicked */
void on_btn1_clicked(GtkWidget *widget, gpointer data) {




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



  if(gv_count == 0){
  bcm2835_gpio_write(PIN, HIGH);
  onimage = gtk_image_new_from_file("lightsOn.png") ;
  gtk_button_set_image (GTK_BUTTON (btn),onimage) ;
  }


  if(gv_count==1 )
  {
    bcm2835_gpio_write(PIN, LOW);
    offimage = gtk_image_new_from_file("lightsoff.png") ;
    gtk_button_set_image (GTK_BUTTON (btn),offimage);
  }

   gv_count+=1 ;

}

/* another callback */
void on_main_window_destroy(GtkWidget *widget, gpointer *data)
{   bcm2835_gpio_write(PIN, LOW);
    bcm2835_close();
    gtk_main_quit ();
}


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

    GtkBuilder  *builder;

    /* init hardware */

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

    // pass main method params to  gtkinit

    gtk_init(&argc, &argv);

    // builder instance  and return pointer address

     builder = gtk_builder_new();
    // grab the galde exml file snd read this in
     gtk_builder_add_from_file (builder, "switch.glade", NULL);

    // return the window object

    window = GTK_WIDGET(gtk_builder_get_object(builder, "main_window"));

     // now read the signals slots that we created in the glade file

    gtk_builder_connect_signals(builder, NULL);

    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);


    // get pointers to the buttons
    btn = GTK_WIDGET(gtk_builder_get_object(builder, "btn1"));


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

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

    gtk_main();

    return (EXIT_SUCCESS);
}