Re: GDK_POINTER_MOTION_HINT_MASK has no effect

[jcupitt gmail com]

On Nov 27, 2007 2:27 AM, Stewart Weiss <stewart weiss acm org> wrote:
> Does anyone know what the real semantics are, and when is_hint is true?

Here's a complete small program that shows mouse events (with hints)
for a drawing area.

--------------
/* compile with
 *      gcc -g -Wall try32.c `pkg-config gtk+-2.0 --cflags --libs`
 */

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

static gboolean
event_cb (GtkWidget * widget, GdkEvent * ev)
{
  gboolean handled;

  handled = FALSE;

  switch (ev->type)
    {
    case GDK_BUTTON_PRESS:
      printf ("button %d press\n", ev->button.button);
      handled = TRUE;
      break;

    case GDK_BUTTON_RELEASE:
      printf ("button %d release\n", ev->button.button);
      handled = TRUE;
      break;

    case GDK_MOTION_NOTIFY:
      /* A hint? Read the position to get the latest value.
       */
      if (ev->motion.is_hint)
        {
          GdkDisplay *display = gtk_widget_get_display (widget);
          GdkScreen *screen;
          int x_root, y_root;

          printf ("seen a hint!\n");

          gdk_display_get_pointer (display, &screen, &x_root, &y_root, NULL);
          ev->motion.x_root = x_root;
          ev->motion.y_root = y_root;
        }

      printf ("motion at %g x %g\n", ev->motion.x_root, ev->motion.y_root);

      if (ev->motion.state & GDK_BUTTON1_MASK)
        printf ("(and btn1 held down)\n");
      if (ev->motion.state & GDK_BUTTON2_MASK)
        printf ("(and btn2 held down)\n");

      handled = TRUE;

      break;

    default:
      break;
    }

  return (handled);
}

int
main (int argc, char **argv)
{
  GtkWidget *win;
  GtkWidget *area;

  gtk_init (&argc, &argv);
  win = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  g_signal_connect (win, "destroy", G_CALLBACK (gtk_main_quit), NULL);

  area = gtk_drawing_area_new ();
  gtk_widget_add_events (GTK_WIDGET (area),
                         GDK_POINTER_MOTION_MASK |
                         GDK_POINTER_MOTION_HINT_MASK |
                         GDK_BUTTON_PRESS_MASK |
                         GDK_BUTTON_RELEASE_MASK);

  gtk_signal_connect_after (GTK_OBJECT (area), "event",
                            GTK_SIGNAL_FUNC (event_cb), NULL);

  gtk_container_add (GTK_CONTAINER (win), area);

  gtk_window_set_default_size (GTK_WINDOW (win), 250, 250);
  gtk_widget_show_all (win);

  gtk_main ();

  return (0);
}
------------------------

You get output like:

seen a hint!
motion at 1367 x 446
seen a hint!
motion at 1368 x 446
button 1 press
seen a hint!
motion at 1368 x 447
(and btn1 held down)
button 2 press
seen a hint!
motion at 1368 x 448
(and btn1 held down)
(and btn2 held down)

John