Question

Hey I am using c++ to write a program which has a drawing area. I need to make it possible to detect mouse signals from the drawing area and draw points at these positions. How can I do this? There are not many forums which help with this stuff and the documentation is not clear. Can somebody please help me?

Answer 1

Drawing in a gtk3 application is done in response to the “draw” signal. You connect a callback function to the “draw” signal, and when gtk+ needs to redraw the window, your callback is invoked.

g_signal_connect (drawingarea, "draw",
                  G_CALLBACK (draw_cb), NULL);

The callback looks something like this:

static gboolean
draw_cb (GtkWidget *widget,
         cairo_t   *cr,
         gpointer   data)
{
  // do your drawing on the provided cairo_t
  // ...

  return FALSE;
}

Now, to handle mouse clicks, you’ll need to connect another callback function to “button-press-event”:

g_signal_connect (drawingarea, "button-press-event",
                  G_CALLBACK (button_press_event_cb), NULL);

See the drawing area reference docs for a small example and the drawing area demo for a complete application.