How to handle double-click events in GTK+3?

Question

I was wondering how to produce double clicks?

Take the following code that draws lines using single clicks http://zetcode.com/gfx/cairo/basicdrawing/:

#include <cairo.h>
#include <gtk/gtk.h>

static void do_drawing(cairo_t *);

struct {
  int count;
  double coordx[100];
  double coordy[100];
} glob;

static gboolean on_draw_event(GtkWidget *widget, cairo_t *cr, 
    gpointer user_data)
{
  do_drawing(cr);

  return FALSE;
}

static void do_drawing(cairo_t *cr)
{
  cairo_set_source_rgb(cr, 0, 0, 0);
  cairo_set_line_width(cr, 0.5);

  int i, j;
  for (i = 0; i <= glob.count - 1; i++ ) {
      for (j = 0; j <= glob.count - 1; j++ ) {
          cairo_move_to(cr, glob.coordx[i], glob.coordy[i]);
          cairo_line_to(cr, glob.coordx[j], glob.coordy[j]);
      }
  }

  glob.count = 0;
  cairo_stroke(cr);    
}

static gboolean clicked(GtkWidget *widget, GdkEventButton *event,
    gpointer user_data)
{
    if (event->button == 1) {
        glob.coordx[glob.count] = event->x;
        glob.coordy[glob.count++] = event->y;
    }

    if (event->button == 3) {
        gtk_widget_queue_draw(widget);
    }

    return TRUE;
}


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

  glob.count = 0;

  gtk_init(&argc, &argv);

  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

  darea = gtk_drawing_area_new();
  gtk_container_add(GTK_CONTAINER(window), darea);

  gtk_widget_add_events(window, GDK_BUTTON_PRESS_MASK);

  g_signal_connect(G_OBJECT(darea), "draw", 
      G_CALLBACK(on_draw_event), NULL); 
  g_signal_connect(window, "destroy",
      G_CALLBACK(gtk_main_quit), NULL);  

  g_signal_connect(window, "button-press-event", 
      G_CALLBACK(clicked), NULL);

  gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
  gtk_window_set_default_size(GTK_WINDOW(window), 400, 300); 
  gtk_window_set_title(GTK_WINDOW(window), "Lines");

  gtk_widget_show_all(window);

  gtk_main();

  return 0;
}

How do I get this program to respond to double clicks events instead of the single clicks?

I cannot find it in this list https://lazka.github.io/pgi-docs/Gtk-3.0/classes/Button.html#Gtk.Button.signals.clicked.

Answer 1

From GdkEventButton:

For double-clicks the order of events will be:

• GDK_BUTTON_PRESS

• GDK_BUTTON_RELEASE

• GDK_BUTTON_PRESS

• GDK_2BUTTON_PRESS

• GDK_BUTTON_RELEASE

Note that the first click is received just like a normal button press, while the second click results in a GDK_2BUTTON_PRESS being received just after the GDK_BUTTON_PRESS.

(...)

For a double click to occur, the second button press must occur within 1/4 of a second of the first.

Each GdkEvent has a GdkEventType field that you can check for GDK_2BUTTON_PRESS or GDK_DOUBLE_BUTTON_PRESS (alias added in 3.6):

a mouse button has been double-clicked (clicked twice within a short period of time). Note that each click also generates a GDK_BUTTON_PRESS event.

in button-press-event callback.

#include <gtk/gtk.h>

gboolean clicked(GtkWidget *widget, GdkEventButton *event, gpointer user_data)
{
    if(event->type == GDK_DOUBLE_BUTTON_PRESS)
        printf("double\n");

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

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    label = gtk_label_new("label");
    gtk_container_add(GTK_CONTAINER(window), label);

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

    gtk_widget_add_events(window, GDK_BUTTON_PRESS_MASK);
    g_signal_connect(window, "button-press-event", G_CALLBACK(clicked), NULL);

    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
    gtk_window_set_default_size(GTK_WINDOW(window), 400, 300);
    gtk_widget_show_all(window);
    gtk_main ();
    return 0;
}