PathGradientBrush类进行渐变颜色的填充

  private void Form1_Paint(object sender, PaintEventArgs e)
  {
      Graphics g = e.Graphics;
      GraphicsPath gp = new GraphicsPath();

      gp.AddLine(, , , );
      gp.AddLine(, , , );
      gp.AddLine(, , , );
      gp.CloseFigure();

     g.FillRectangle(Brushes.White,this.ClientRectangle);
     g.SmoothingMode = SmoothingMode.AntiAlias;   //反锯齿

    PathGradientBrush pgb = new PathGradientBrush(gp);
     pgb.CenterColor = Color.White;
     pgb.SurroundColors = new Color[]
     {
          Color.Blue
      };
      g.FillPath(pgb,gp);
      g.DrawPath(Pens.Black,gp);
      pgb.Dispose();
      gp.Dispose();
 }

GraphicsPath：可以添加自定义的由一系列相互连接的直线、曲线连接起来组成的开放（非闭合）图形。
   创建路径时就会隐式创建一个新图形（由上面的直线、曲线等组成）