protected void ComputePosition(Gdk.Rectangle area, out double x, out double y)
{
double cell_width = area.Width - 2 * Xpad;
double cell_height = area.Height - 2 * Ypad;
double stars_width = MaxRating * Size;
double stars_height = Size;
x = area.X + Xpad + (cell_width - stars_width) / 2.0;
y = area.Y + Ypad + (cell_height - stars_height) / 2.0;
}