81 lines
3.8 KiB
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81 lines
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<title>Use GdkEventExpose.region: GTK+ 3 Reference Manual</title>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="checklist-gdkeventexpose-region"></a>Use GdkEventExpose.region</h2></div></div></div>
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<p><b>Why. </b>
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The <em class="structfield"><code>region</code></em> field of
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<span class="structname">GdkEventExpose</span> allows you to redraw
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less than the traditional <em class="structfield"><code>GdkEventRegion.area</code></em>.
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</p>
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<p>
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In early GTK+ versions, the <span class="structname">GdkEventExpose</span>
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structure only had an <em class="structfield"><code>area</code></em> field to
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let you determine the region that you needed to redraw. In current
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GTK+, this field still exists for compatibility and as a simple
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interface. However, there is also a <em class="structfield"><code>region</code></em>
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field which contains a fine-grained region. The
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<em class="structfield"><code>area</code></em> field is simply the bounding rectangle
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of the <em class="structfield"><code>region</code></em>.
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</p>
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<p>
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Widgets that are very expensive to re-render, such as an image
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editor, may prefer to use the
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<em class="structfield"><code>GdkEventExpose.region</code></em> field to paint
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as little as possible. Widgets that just use a few drawing
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primitives, such as labels and buttons, may prefer to use the
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traditional <em class="structfield"><code>GdkEventExpose.area</code></em> field
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for simplicity.
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</p>
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<p>
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Regions have an internal representation that is accessible as a
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list of rectangles. To turn the
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<em class="structfield"><code>GdkEventExpose.region</code></em> field into such
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a list, use <code class="function">gdk_region_get_rectangles()</code>:
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</p>
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<a name="gdkregion-get-rectangles"></a><pre class="programlisting">
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static gboolean
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my_widget_expose_event_handler (GtkWidget *widget, GdkEventExpose *event)
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{
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GdkRectangle *rects;
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int n_rects;
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int i;
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gdk_region_get_rectangles (event->region, &rects, &n_rects);
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for (i = 0; i < n_rects; i++)
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{
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/* Repaint rectangle: (rects[i].x, rects[i].y),
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* (rects[i].width, rects[i].height)
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*/
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}
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g_free (rects);
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return FALSE;
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}
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</pre>
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