繼承System.Windows.Forms.Form窗體類時，重載其畫窗體形狀的事件OnPaint,就可以畫出各種自定義的窗體形狀。例子代碼是畫一個圓形窗體。
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);//這句是很重要的，設定窗體顯示的區域為你所畫的區域。
}