#include <gtk/gtk.h>

/* This is a callback function. The data arguments are ignored
 * in this example. More on callbacks below.
 */
static void
print_hello (GtkWidget *widget,
     gpointer   data)
{
  g_print ("Hello World\n");
}

static gboolean
on_delete_event (GtkWidget *widget,
         GdkEvent  *event,
         gpointer   data)
{
  /* If you return FALSE in the "delete_event" signal handler,
   * GTK will emit the "destroy" signal. Returning TRUE means
   * you don't want the window to be destroyed.
   *
   * This is useful for popping up 'are you sure you want to quit?'
   * type dialogs.
   */

  g_print ("delete event occurred\n");

  return TRUE;
}

int
main (int   argc,
      char *argv[])
{
  /* GtkWidget is the storage type for widgets */
  GtkWidget *window;
  GtkWidget *button;

  /* This is called in all GTK applications. Arguments are parsed
   * from the command line and are returned to the application.
   */
  gtk_init (&argc, &argv);

  /* create a new window, and set its title */
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_window_set_title (GTK_WINDOW (window), "Hello");

  /* When the window emits the "delete-event" signal (which is emitted
   * by GTK+ in response to an event coming from the window manager,
   * usually as a result of clicking the "close" window control), we
   * ask it to call the on_delete_event() function as defined above.
   *
   * The data passed to the callback function is NULL and is ignored
   * in the callback function.
   */
  g_signal_connect (window, "delete-event", G_CALLBACK (on_delete_event), NULL);

  /* Here we connect the "destroy" event to the gtk_main_quit() function.
   *
   * This signal is emitted when we call gtk_widget_destroy() on the window,
   * or if we return FALSE in the "delete_event" callback.
   */
  g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL);

  /* Sets the border width of the window. */
  gtk_container_set_border_width (GTK_CONTAINER (window), 10);

  /* Creates a new button with the label "Hello World". */
  button = gtk_button_new_with_label ("Hello World");

  /* When the button receives the "clicked" signal, it will call the
   * function print_hello() passing it NULL as its argument.
   *
   * The print_hello() function is defined above.
   */
  g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);

  /* The g_signal_connect_swapped() function will connect the "clicked" signal
   * of the button to the gtk_widget_destroy() function; instead of calling it
   * using the button as its argument, it will swap it with the user data
   * argument. This will cause the window to be destroyed by calling
   * gtk_widget_destroy() on the window.
   */
  g_signal_connect_swapped (button, "clicked", G_CALLBACK (gtk_widget_destroy), window);

  /* This packs the button into the window. A GtkWindow inherits from GtkBin,
   * which is a special container that can only have one child
   */
  gtk_container_add (GTK_CONTAINER (window), button);

  /* The final step is to display this newly created widget... */
  gtk_widget_show (button);

  /* ... and the window */
  gtk_widget_show (window);

  /* All GTK applications must have a gtk_main(). Control ends here
   * and waits for an event to occur (like a key press or a mouse event),
   * until gtk_main_quit() is called.
   */
  gtk_main ();

  return 0;
}

#include <gtk/gtk.h>

static void
print_hello (GtkWidget *widget,
     gpointer   data)
{
  g_print ("Hello World\n");
}

int
main (int   argc,
      char *argv[])
{
  GtkWidget *window;
  GtkWidget *grid;
  GtkWidget *button;

  /* This is called in all GTK applications. Arguments are parsed
   * from the command line and are returned to the application.
   */
  gtk_init (&argc, &argv);

  /* create a new window, and set its title */
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_window_set_title (GTK_WINDOW (window), "Grid");
  g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL);
  gtk_container_set_border_width (GTK_CONTAINER (window), 10);

  /* Here we construct the container that is going pack our buttons */
  grid = gtk_grid_new ();

  /* Pack the container in the window */
  gtk_container_add (GTK_CONTAINER (window), grid);

  button = gtk_button_new_with_label ("Button 1");
  g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);

  /* Place the first button in the grid cell (0, 0), and make it fill
   * just 1 cell horizontally and vertically (ie no spanning)
   */
  gtk_grid_attach (GTK_GRID (grid), button, 0, 0, 1, 1);

  button = gtk_button_new_with_label ("Button 2");
  g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);

  /* Place the second button in the grid cell (1, 0), and make it fill
   * just 1 cell horizontally and vertically (ie no spanning)
   */
  gtk_grid_attach (GTK_GRID (grid), button, 1, 0, 1, 1);

  button = gtk_button_new_with_label ("Quit");
  g_signal_connect (button, "clicked", G_CALLBACK (gtk_main_quit), NULL);

  /* Place the Quit button in the grid cell (0, 1), and make it
   * span 2 columns.
   */
  gtk_grid_attach (GTK_GRID (grid), button, 0, 1, 2, 1);

  /* Now that we are done packing our widgets, we show them all
   * in one go, by calling gtk_widget_show_all() on the window.
   * This call recursively calls gtk_widget_show() on all widgets
   * that are contained in the window, directly or indirectly.
   */
  gtk_widget_show_all (window);

  /* All GTK applications must have a gtk_main(). Control ends here
   * and waits for an event to occur (like a key press or a mouse event),
   * until gtk_main_quit() is called.
   */
  gtk_main ();

  return 0;
}

#include <gtk/gtk.h>

/* Surface to store current scribbles */
static cairo_surface_t *surface = NULL;

static void
clear_surface (void)
{
  cairo_t *cr;

  cr = cairo_create (surface);

  cairo_set_source_rgb (cr, 1, 1, 1);
  cairo_paint (cr);

  cairo_destroy (cr);
}

/* Create a new surface of the appropriate size to store our scribbles */
static gboolean
configure_event_cb (GtkWidget         *widget,
            GdkEventConfigure *event,
            gpointer           data)
{
  if (surface)
    cairo_surface_destroy (surface);

  surface = gdk_window_create_similar_surface (gtk_widget_get_window (widget),
                                       CAIRO_CONTENT_COLOR,
                                       gtk_widget_get_allocated_width (widget),
                                       gtk_widget_get_allocated_height (widget));

  /* Initialize the surface to white */
  clear_surface ();

  /* We've handled the configure event, no need for further processing. */
  return TRUE;
}

/* Redraw the screen from the surface. Note that the ::draw
 * signal receives a ready-to-be-used cairo_t that is already
 * clipped to only draw the exposed areas of the widget
 */
static gboolean
draw_cb (GtkWidget *widget,
 cairo_t   *cr,
 gpointer   data)
{
  cairo_set_source_surface (cr, surface, 0, 0);
  cairo_paint (cr);

  return FALSE;
}

/* Draw a rectangle on the surface at the given position */
static void
draw_brush (GtkWidget *widget,
    gdouble    x,
    gdouble    y)
{
  cairo_t *cr;

  /* Paint to the surface, where we store our state */
  cr = cairo_create (surface);

  cairo_rectangle (cr, x - 3, y - 3, 6, 6);
  cairo_fill (cr);

  cairo_destroy (cr);

  /* Now invalidate the affected region of the drawing area. */
  gtk_widget_queue_draw_area (widget, x - 3, y - 3, 6, 6);
}

/* Handle button press events by either drawing a rectangle
 * or clearing the surface, depending on which button was pressed.
 * The ::button-press signal handler receives a GdkEventButton
 * struct which contains this information.
 */
static gboolean
button_press_event_cb (GtkWidget      *widget,
               GdkEventButton *event,
               gpointer        data)
{
  /* paranoia check, in case we haven't gotten a configure event */
  if (surface == NULL)
    return FALSE;

  if (event->button == 1)
    {
      draw_brush (widget, event->x, event->y);
    }
  else if (event->button == 3)
    {
      clear_surface ();
      gtk_widget_queue_draw (widget);
    }

  /* We've handled the event, stop processing */
  return TRUE;
}

/* Handle motion events by continuing to draw if button 1 is
 * still held down. The ::motion-notify signal handler receives
 * a GdkEventMotion struct which contains this information.
 */
static gboolean
motion_notify_event_cb (GtkWidget      *widget,
                GdkEventMotion *event,
                gpointer        data)
{
  int x, y;
  GdkModifierType state;

  /* paranoia check, in case we haven't gotten a configure event */
  if (surface == NULL)
    return FALSE;

  /* This call is very important; it requests the next motion event.
   * If you don't call gdk_window_get_pointer() you'll only get
   * a single motion event. The reason is that we specified
   * GDK_POINTER_MOTION_HINT_MASK to gtk_widget_set_events().
   * If we hadn't specified that, we could just use event->x, event->y
   * as the pointer location. But we'd also get deluged in events.
   * By requesting the next event as we handle the current one,
   * we avoid getting a huge number of events faster than we
   * can cope.
   */
  gdk_window_get_pointer (event->window, &x, &y, &state);

  if (state & GDK_BUTTON1_MASK)
    draw_brush (widget, x, y);

  /* We've handled it, stop processing */
  return TRUE;
}

static void
close_window (void)
{
  if (surface)
    cairo_surface_destroy (surface);

  gtk_main_quit ();
}

int
main (int   argc,
      char *argv[])
{
  GtkWidget *window;
  GtkWidget *frame;
  GtkWidget *da;

  gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_window_set_title (GTK_WINDOW (window), "Drawing Area");

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

  gtk_container_set_border_width (GTK_CONTAINER (window), 8);

  frame = gtk_frame_new (NULL);
  gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_IN);
  gtk_container_add (GTK_CONTAINER (window), frame);

  da = gtk_drawing_area_new ();
  /* set a minimum size */
  gtk_widget_set_size_request (da, 100, 100);

  gtk_container_add (GTK_CONTAINER (frame), da);

  /* Signals used to handle the backing surface */
  g_signal_connect (da, "draw",
            G_CALLBACK (draw_cb), NULL);
  g_signal_connect (da,"configure-event",
            G_CALLBACK (configure_event_cb), NULL);

  /* Event signals */
  g_signal_connect (da, "motion-notify-event",
            G_CALLBACK (motion_notify_event_cb), NULL);
  g_signal_connect (da, "button-press-event",
            G_CALLBACK (button_press_event_cb), NULL);

  /* Ask to receive events the drawing area doesn't normally
   * subscribe to. In particular, we need to ask for the
   * button press and motion notify events that want to handle.
   */
  gtk_widget_set_events (da, gtk_widget_get_events (da)
                     | GDK_BUTTON_PRESS_MASK
                     | GDK_POINTER_MOTION_MASK
                     | GDK_POINTER_MOTION_HINT_MASK);

  gtk_widget_show_all (window);

  gtk_main ();

  return 0;
}