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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="checklist-gdkeventexpose-region"></a>Use GdkEventExpose.region</h2></div></div></div>
<p><b>Why. </b>
The <em class="structfield"><code>region</code></em> field of
<span class="structname">GdkEventExpose</span> allows you to redraw
less than the traditional
<em class="structfield"><code>GdkEventRegion.area</code></em>.
</p>
<p>
In GTK+ 1.x, the <span class="structname">GdkEventExpose</span>
structure only had an <em class="structfield"><code>area</code></em> field to
let you determine the region that you needed to redraw. In GTK+
2.x, this field exists for compatibility and as a simple
interface. However, there is also a
<em class="structfield"><code>region</code></em> field which contains a
fine-grained region. The <em class="structfield"><code>area</code></em> field
is simply the bounding rectangle of the
<em class="structfield"><code>region</code></em>.
</p>
<p>
Widgets that are very expensive to re-render, such as an image
editor, may prefer to use the
<em class="structfield"><code>GdkEventExpose.region</code></em> field to paint
as little as possible. Widgets that just use a few drawing
primitives, such as labels and buttons, may prefer to use the
traditional <em class="structfield"><code>GdkEventExpose.area</code></em> field
for simplicity.
</p>
<p>
Regions have an internal representation that is accessible as a
list of rectangles. To turn the
<em class="structfield"><code>GdkEventExpose.region</code></em> field into such
a list, use <a href="../html/gdk2-Points-Rectangles-and-Regions.html#gdk-region-get-rectangles"><code class="function">gdk_region_get_rectangles()</code></a>:
</p>
<a name="gdkregion-get-rectangles"></a><pre class="programlisting">
static gboolean
my_widget_expose_event_handler (GtkWidget *widget, GdkEventExpose *event)
{
GdkRectangle *rects;
int n_rects;
int i;
gdk_region_get_rectangles (event->region, &rects, &n_rects);
for (i = 0; i < n_rects; i++)
{
/* Repaint rectangle: (rects[i].x, rects[i].y),
* (rects[i].width, rects[i].height)
*/
}
g_free (rects);
return FALSE;
}
</pre>
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