vDrawCurve()方法
该法用光滑的曲线把给定的点连接起来，常用形式有
public void DrawCurve(Pen pen, Point[] points)
其中，Point结构类型的数组中指明各节点，默认弯曲强度为0.5，注意数组中至少要有4个元素。
public void DrawCurve(Pen pen, Point[] points, float tension)
其中tension指定弯曲强度，该值范围为0.0f ～1.0f，超出此范围会产生异常，当弯曲强度为零时，就是直线
演示：
private void Form1_Paint(object sender,
System.Windows.Forms.PaintEventArgs e)
{
Pen redPen = new Pen(Color.Red, 3);
Pen greenPen = new Pen(Color.Green, 3);
Point[] curvePoints =
{
new Point( 50, 250),
new Point(100, 25),
new Point(200, 250),
new Point(250, 50),
new Point(300, 75),
new Point(350, 200),
new Point(400, 150)
};
e.Graphics.DrawLines(redPen, curvePoints);
e.Graphics.DrawCurve(greenPen, curvePoints);
}
