gtkdrawingarea.sgml

This GTK+ version 2.12.3. GTK+ is a multi-platform toolkit for creating graphical user interfaces.

<!-- ##### SECTION Title ##### -->
GtkDrawingArea

<!-- ##### SECTION Short_Description ##### -->
A widget for custom user interface elements

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<para>

The #GtkDrawingArea widget is used for creating custom user interface
elements. It's essentially a blank widget; you can draw on
<literal>widget-&gt;window</literal>. After creating a drawing area,
the application may want to connect to:

<itemizedlist>
  <listitem>
    <para>
    Mouse and button press signals to respond to input from
    the user. (Use gtk_widget_add_events() to enable events 
    you wish to receive.)
    </para>
  </listitem>
  <listitem>
    <para>
    The "realize" signal to take any necessary actions
    when the widget is instantiated on a particular display.
    (Create GDK resources in response to this signal.)
    </para>
  </listitem>
  <listitem>
    <para>
    The "configure_event" signal to take any necessary actions
    when the widget changes size.
    </para>
  </listitem>
  <listitem>
    <para>
    The "expose_event" signal to handle redrawing the
    contents of the widget.
    </para>
  </listitem>
</itemizedlist>
</para>
<para>
The following code portion demonstrates using a drawing
area to display a circle in the normal widget foreground 
color.
Note that GDK automatically clears the exposed area
to the background color before sending the expose event, and 
that drawing is implicitly clipped to the exposed area.
</para>
<example>
<title>Simple <structname>GtkDrawingArea</structname> usage.</title>
<programlisting>
gboolean
expose_event_callback (GtkWidget *widget, GdkEventExpose *event, gpointer data)
{
  gdk_draw_arc (widget->window,
                widget->style->fg_gc[GTK_WIDGET_STATE (widget)],
                TRUE,
                0, 0, widget->allocation.width, widget->allocation.height,
                0, 64 * 360);
 
  return TRUE;
}
[...]
  GtkWidget *drawing_area = gtk_drawing_area_new (<!-- -->);
  gtk_widget_set_size_request (drawing_area, 100, 100);
  g_signal_connect (G_OBJECT (drawing_area), "expose_event",  
                    G_CALLBACK (expose_event_callback), NULL);
</programlisting>
</example>

<para>
Expose events are normally delivered when a drawing area first comes
onscreen, or when it's covered by another window and then uncovered
(exposed). You can also force an expose event by adding to the "damage
region" of the drawing area's window; gtk_widget_queue_draw_area() and
gdk_window_invalidate_rect() are equally good ways to do this. You'll
then get an expose event for the invalid region.
</para>

<para>
The available routines for drawing are documented on the <link
linkend="gdk-Drawing-Primitives">GDK Drawing Primitives</link> page.
See also gdk_draw_pixbuf() for drawing a #GdkPixbuf.
</para>

<para>
To receive mouse events on a drawing area, you will need to enable
them with gtk_widget_add_events(). To receive keyboard events, you
will need to set the #GTK_CAN_FOCUS flag on the drawing area, and
should probably draw some user-visible indication that the drawing
area is focused. Use the GTK_HAS_FOCUS() macro in your expose event
handler to decide whether to draw the focus indicator. See
gtk_paint_focus() for one way to draw focus.
</para>

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<para>
Sometimes #GtkImage is a useful alternative to a drawing area. 
You can put a #GdkPixmap in the #GtkImage and draw to the #GdkPixmap, 
calling gtk_widget_queue_draw() on the #GtkImage when you want to 
refresh to the screen.
</para>

<!-- ##### SECTION Stability_Level ##### -->


<!-- ##### STRUCT GtkDrawingArea ##### -->
<para>
The #GtkDrawingArea struct contains private data only, and
should be accessed using the functions below.
</para>


<!-- ##### FUNCTION gtk_drawing_area_new ##### -->
<para>
Creates a new drawing area.
</para>

@Returns: a new #GtkDrawingArea


<!-- ##### FUNCTION gtk_drawing_area_size ##### -->
<para>
(Use gtk_widget_set_size_request() instead.)
Sets the size that the drawing area will request
in response to a "size_request" signal. The 
drawing area may actually be allocated a size
larger than this depending on how it is packed
within the enclosing containers.
</para>

@darea: a #GtkDrawingArea.
@width: the width to request.
@height: the height to request.