docs/reference/gtk/html/checklist-gdkeventexpose-region.html

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  24 <a name="checklist-gdkeventexpose-region"></a>Use GdkEventExpose.region</h2></div></div></div>
  25 <p><b>Why. </b>
  26         The <em class="structfield"><code>region</code></em> field of
  27         <span class="structname">GdkEventExpose</span> allows you to redraw
  28         less than the traditional <em class="structfield"><code>GdkEventRegion.area</code></em>.
  29       </p>
  30 <p>
  31       In early GTK+ versions, the <span class="structname">GdkEventExpose</span>
  32       structure only had an <em class="structfield"><code>area</code></em> field to
  33       let you determine the region that you needed to redraw. In current
  34       GTK+, this field still exists for compatibility and as a simple
  35       interface. However, there is also a <em class="structfield"><code>region</code></em>
  36       field which contains a fine-grained region. The
  37       <em class="structfield"><code>area</code></em> field is simply the bounding rectangle
  38       of the <em class="structfield"><code>region</code></em>.
  39     </p>
  40 <p>
  41       Widgets that are very expensive to re-render, such as an image
  42       editor, may prefer to use the
  43       <em class="structfield"><code>GdkEventExpose.region</code></em> field to paint
  44       as little as possible.  Widgets that just use a few drawing
  45       primitives, such as labels and buttons, may prefer to use the
  46       traditional <em class="structfield"><code>GdkEventExpose.area</code></em> field
  47       for simplicity.
  48     </p>
  49 <p>
  50       Regions have an internal representation that is accessible as a
  51       list of rectangles.  To turn the
  52       <em class="structfield"><code>GdkEventExpose.region</code></em> field into such
  53       a list, use <code class="function">gdk_region_get_rectangles()</code>:
  54     </p>
  55 <a name="gdkregion-get-rectangles"></a><pre class="programlisting">
  56 static gboolean
  57 my_widget_expose_event_handler (GtkWidget *widget, GdkEventExpose *event)
  58 {
  59   GdkRectangle *rects;
  60   int n_rects;
  61   int i;
  62
  63   gdk_region_get_rectangles (event-&gt;region, &amp;rects, &amp;n_rects);
  64
  65   for (i = 0; i &lt; n_rects; i++)
  66     {
  67       /* Repaint rectangle: (rects[i].x, rects[i].y),
  68        *                    (rects[i].width, rects[i].height)
  69        */
  70     }
  71
  72   g_free (rects);
  73
  74   return FALSE;
  75 }
  76     </pre>
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