private void DrawGrid(Context g)
{
g.Color = new Color (0.05, 0.05, 0.05);
g.SetDash (new double[] {4, 4}, 2);
g.LineWidth = 1;
for (int i = 1; i < 4; i++) {
g.MoveTo (i * size / 4, 0);
g.LineTo (i * size / 4, size);
g.MoveTo (0, i * size / 4);
g.LineTo (size, i * size / 4);
}
g.MoveTo (0, size - 1);
g.LineTo (size - 1, 0);
g.Stroke ();
g.SetDash (new double[] {}, 0);
}