sec-addingxinputsupport.html

gtk 开发手册和参考文档。 包括gtk glib gdk等

segfault.)</P
><P
>The InputDialog has two buttons "Close" and "Save", which by default
have no actions assigned to them. In the above function we make
"Close" hide the dialog, hide the "Save" button, since we don't
implement saving of XInput options in this program.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN2919"
>25.4.2. Using extended device information</A
></H2
><P
>Once we've enabled the device, we can just use the extended 
device information in the extra fields of the event structures.
In fact, it is always safe to use this information since these
fields will have reasonable default values even when extended
events are not enabled.</P
><P
>Once change we do have to make is to call
<TT
CLASS="LITERAL"
>gdk_input_window_get_pointer()</TT
> instead of
<TT
CLASS="LITERAL"
>gdk_window_get_pointer</TT
>. This is necessary because
<TT
CLASS="LITERAL"
>gdk_window_get_pointer</TT
> doesn't return the extended device
information.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>void gdk_input_window_get_pointer( GdkWindow       *window,
                                   guint32         deviceid,
                                   gdouble         *x,
                                   gdouble         *y,
                                   gdouble         *pressure,
                                   gdouble         *xtilt,
                                   gdouble         *ytilt,
                                   GdkModifierType *mask);</PRE
></TD
></TR
></TABLE
><P
>When calling this function, we need to specify the device ID as
well as the window. Usually, we'll get the device ID from the
<TT
CLASS="LITERAL"
>deviceid</TT
> field of an event structure. Again, this function
will return reasonable values when extension events are not
enabled. (In this case, <TT
CLASS="LITERAL"
>event-&#62;deviceid</TT
> will have the value
<TT
CLASS="LITERAL"
>GDK_CORE_POINTER</TT
>).</P
><P
>So the basic structure of our button-press and motion event handlers
doesn't change much - we just need to add code to deal with the
extended information.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>static gint
button_press_event (GtkWidget *widget, GdkEventButton *event)
{
  print_button_press (event-&#62;deviceid);
  
  if (event-&#62;button == 1 &#38;&#38; pixmap != NULL)
    draw_brush (widget, event-&#62;source, event-&#62;x, event-&#62;y, event-&#62;pressure);

  return TRUE;
}

static gint
motion_notify_event (GtkWidget *widget, GdkEventMotion *event)
{
  gdouble x, y;
  gdouble pressure;
  GdkModifierType state;

  if (event-&#62;is_hint)
    gdk_input_window_get_pointer (event-&#62;window, event-&#62;deviceid,
				  &#38;x, &#38;y, &#38;pressure, NULL, NULL, &#38;state);
  else
    {
      x = event-&#62;x;
      y = event-&#62;y;
      pressure = event-&#62;pressure;
      state = event-&#62;state;
    }
    
  if (state &#38; GDK_BUTTON1_MASK &#38;&#38; pixmap != NULL)
    draw_brush (widget, event-&#62;source, x, y, pressure);
  
  return TRUE;
}</PRE
></TD
></TR
></TABLE
><P
>We also need to do something with the new information. Our new
<TT
CLASS="LITERAL"
>draw_brush()</TT
> function draws with a different color for
each <TT
CLASS="LITERAL"
>event-&#62;source</TT
> and changes the brush size depending
on the pressure.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>/* Draw a rectangle on the screen, size depending on pressure,
   and color on the type of device */
static void
draw_brush (GtkWidget *widget, GdkInputSource source,
	    gdouble x, gdouble y, gdouble pressure)
{
  GdkGC *gc;
  GdkRectangle update_rect;

  switch (source)
    {
    case GDK_SOURCE_MOUSE:
      gc = widget-&#62;style-&#62;dark_gc[GTK_WIDGET_STATE (widget)];
      break;
    case GDK_SOURCE_PEN:
      gc = widget-&#62;style-&#62;black_gc;
      break;
    case GDK_SOURCE_ERASER:
      gc = widget-&#62;style-&#62;white_gc;
      break;
    default:
      gc = widget-&#62;style-&#62;light_gc[GTK_WIDGET_STATE (widget)];
    }

  update_rect.x = x - 10 * pressure;
  update_rect.y = y - 10 * pressure;
  update_rect.width = 20 * pressure;
  update_rect.height = 20 * pressure;
  gdk_draw_rectangle (pixmap, gc, TRUE,
		      update_rect.x, update_rect.y,
		      update_rect.width, update_rect.height);
  gtk_widget_draw (widget, &#38;update_rect);
}</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN2937"
>25.4.3. Finding out more about a device</A
></H2
><P
>As an example of how to find out more about a device, our program
will print the name of the device that generates each button
press. To find out the name of a device, we call the function:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>GList *gdk_input_list_devices               (void);</PRE
></TD
></TR
></TABLE
><P
>which returns a GList (a linked list type from the GLib library)
of GdkDeviceInfo structures. The GdkDeviceInfo structure is defined
as:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>struct _GdkDeviceInfo
{
  guint32 deviceid;
  gchar *name;
  GdkInputSource source;
  GdkInputMode mode;
  gint has_cursor;
  gint num_axes;
  GdkAxisUse *axes;
  gint num_keys;
  GdkDeviceKey *keys;
};</PRE
></TD
></TR
></TABLE
><P
>Most of these fields are configuration information that you can ignore
unless you are implementing XInput configuration saving. The fieldwe
are interested in here is <TT
CLASS="LITERAL"
>name</TT
> which is simply the name that X
assigns to the device. The other field that isn't configuration
information is <TT
CLASS="LITERAL"
>has_cursor</TT
>. If <TT
CLASS="LITERAL"
>has_cursor</TT
> is false, then we
we need to draw our own cursor. But since we've specified
<TT
CLASS="LITERAL"
>GDK_EXTENSION_EVENTS_CURSOR</TT
>, we don't have to worry about this.</P
><P
>Our <TT
CLASS="LITERAL"
>print_button_press()</TT
> function simply iterates through
the returned list until it finds a match, then prints out
the name of the device.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>static void
print_button_press (guint32 deviceid)
{
  GList *tmp_list;

  /* gdk_input_list_devices returns an internal list, so we shouldn't
     free it afterwards */
  tmp_list = gdk_input_list_devices();

  while (tmp_list)
    {
      GdkDeviceInfo *info = (GdkDeviceInfo *)tmp_list-&#62;data;

      if (info-&#62;deviceid == deviceid)
	{
	  printf("Button press on device '%s'\n", info-&#62;name);
	  return;
	}

      tmp_list = tmp_list-&#62;next;
    }
}</PRE
></TD
></TR
></TABLE
><P
>That completes the changes to "XInputize" our program.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SEC-FURTHERSOPHISTICATIONS"
>25.4.4. Further sophistications</A
></H2
><P
>Although our program now supports XInput quite well, it lacks some
features we would want in a full-featured application. First, the user
probably doesn't want to have to configure their device each time they
run the program, so we should allow them to save the device
configuration. This is done by iterating through the return of
<TT
CLASS="LITERAL"
>gdk_input_list_devices()</TT
> and writing out the configuration to a
file.</P
><P
>To restore the state next time the program is run, GDK provides
functions to change device configuration:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>gdk_input_set_extension_events()
gdk_input_set_source()
gdk_input_set_mode()
gdk_input_set_axes()
gdk_input_set_key()</PRE
></TD
></TR
></TABLE
><P
>(The list returned from <TT
CLASS="LITERAL"
>gdk_input_list_devices()</TT
> should not be
modified directly.) An example of doing this can be found in the
drawing program gsumi. (Available from <A
HREF="http://www.msc.cornell.edu/~otaylor/gsumi/"
TARGET="_top"
>http://www.msc.cornell.edu/~otaylor/gsumi/</A
>) Eventually, it
would be nice to have a standard way of doing this for all
applications. This probably belongs at a slightly higher level than
GTK, perhaps in the GNOME library.</P
><P
>Another major omission that we have mentioned above is the lack of
cursor drawing. Platforms other than XFree86 currently do not allow
simultaneously using a device as both the core pointer and directly by
an application. See the <A
HREF="http://www.msc.cornell.edu/~otaylor/xinput/XInput-HOWTO.html"
TARGET="_top"
>XInput-HOWTO</A
> for more information about this. This means that
applications that want to support the widest audience need to draw
their own cursor.</P
><P
>An application that draws its own cursor needs to do two things:
determine if the current device needs a cursor drawn or not, and
determine if the current device is in proximity. (If the current
device is a drawing tablet, it's a nice touch to make the cursor 
disappear when the stylus is lifted from the tablet. When the
device is touching the stylus, that is called "in proximity.")
The first is done by searching the device list, as we did
to find out the device name. The second is achieved by selecting
"proximity_out" events. An example of drawing one's own cursor is
found in the "testinput" program found in the GTK distribution.</P
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="sec-thedrawingareawidget.html"
>&#60;&#60;&#60; Previous</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="gtk-tut.html"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="ch-tips.html"
>Next &#62;&#62;&#62;</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>The DrawingArea Widget, And Drawing</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="ch-scribble.html"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Tips For Writing GTK Applications</TD
></TR
></TABLE
></DIV
>    
    </td>
    </tr></table>
  </td>
  </tr>
</table>
</body>
</BODY
></HTML
>