void SetSamplePoint(Gdk.Point p)
{
region.X = p.X;
region.Y = p.Y;
region.Width = 2 * radius;
region.Height = 2 * radius;
if (view.Pixbuf != null)
{
region.Offset(-Math.Min(region.X, Math.Max(region.Right - view.Pixbuf.Width, radius)),
-Math.Min(region.Y, Math.Max(region.Bottom - view.Pixbuf.Height, radius)));
region.Intersect(new Gdk.Rectangle(0, 0, view.Pixbuf.Width, view.Pixbuf.Height));
}
UpdateSample();
}