static public void DrawNode(ICanvas canvas, UnitPoint nodepoint)
{
RectangleF r = new RectangleF(canvas.ToScreen(nodepoint), new SizeF(0, 0));
r.Inflate(3, 3);
if (r.Right < 0 || r.Left > canvas.ClientRectangle.Width)
return;
if (r.Top < 0 || r.Bottom > canvas.ClientRectangle.Height)
return;
canvas.Graphics.FillRectangle(Brushes.White, r);
r.Inflate(1, 1);
canvas.Graphics.DrawRectangle(Pens.Black, ScreenUtils.ConvertRect(r));
}