一个画任意形状的窗体的例子

继承System.Windows.Forms.Form窗体类时，重载其画窗体形状的事件OnPaint,就可以画出各种自定义的窗体形状。例子代码是画一个圆形窗体。
protected override void OnPaint(PaintEventArgs e)
        {
       GraphicsPath gp = new GraphicsPath();
       gp.AddEllipse(20,20,110,110);
       //gp.AddLine(30,30,110,110);
    
       Matrix RotationTransform = new Matrix(1,0, 0,1,1,1);    // rotation matrix
       //Matrix TranslationTransform = new Matrix(1, 0, 0, 1, 0, 0); // translation matrix
       PointF TheRotationPoint = new PointF(110.0f, 110.0f);    // rotation point     
       // rotate the rotation transformation matrix f degrees around TheRotationPoint
       RotationTransform.RotateAt(f, TheRotationPoint);     
       //Call the Transform method of the Graphics Path in order to multiply it by the rotation matrix and rotate the balloon
       gp.Transform(RotationTransform);
       e.Graphics.DrawPath(Pens.Black, gp);
       f=f+10;
       this.Region=new Region(gp);//这句是很重要的，设定窗体显示的区域为你所画的区域。
        }