| GTK+ 3 Reference Manual |
|---|
Why.
The region field of
GdkEventExpose allows you to redraw
less than the traditional GdkEventRegion.area.
In early GTK+ versions, the GdkEventExpose
structure only had an area field to
let you determine the region that you needed to redraw. In current
GTK+, this field still exists for compatibility and as a simple
interface. However, there is also a region
field which contains a fine-grained region. The
area field is simply the bounding rectangle
of the region.
Widgets that are very expensive to re-render, such as an image
editor, may prefer to use the
GdkEventExpose.region 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 GdkEventExpose.area field
for simplicity.
Regions have an internal representation that is accessible as a
list of rectangles. To turn the
GdkEventExpose.region field into such
a list, use gdk_region_get_rectangles():
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;
}