protected void Page_Load(object sender, EventArgs e)
{
 Bitmap bm = new Bitmap(800, 600);
 Graphics g = Graphics.FromImage(bm);
 g.FillRectangle(Brushes.White,new Rectangle(0,0,800,600));
 FillRoundRectangle(g,Brushes.Plum,new Rectangle(100, 100, 100, 100), 8);
 DrawRoundRectangle(g, Pens.Yellow,new Rectangle(100, 100, 100, 100), 8);
 bm.Save(Response.OutputStream, ImageFormat.Jpeg);
 g.Dispose();
 bm.Dispose();
}
public static void DrawRoundRectangle(Graphics g,Pen pen,Rectangle rect, int cornerRadius)
{
 using (GraphicsPath path = CreateRoundedRectanglePath(rect, cornerRadius))
 {
  g.DrawPath(pen, path);
 }
}
public static void FillRoundRectangle(Graphics g, Brush brush,Rectangle rect, int cornerRadius)
{
 using (GraphicsPath path = CreateRoundedRectanglePath(rect, cornerRadius))
 {
  g.FillPath(brush, path);
 }
}
internal static GraphicsPath CreateRoundedRectanglePath(Rectangle rect, int cornerRadius)
{
 GraphicsPath roundedRect = new GraphicsPath();
 roundedRect.AddArc(rect.X, rect.Y, cornerRadius * 2, cornerRadius * 2, 180, 90);
 roundedRect.AddLine(rect.X + cornerRadius, rect.Y, rect.Right - cornerRadius * 2, rect.Y);
 roundedRect.AddArc(rect.X + rect.Width - cornerRadius * 2, rect.Y, cornerRadius * 2, cornerRadius * 2, 270, 90);
 roundedRect.AddLine(rect.Right, rect.Y + cornerRadius * 2, rect.Right, rect.Y + rect.Height - cornerRadius * 2);
 roundedRect.AddArc(rect.X + rect.Width - cornerRadius * 2, rect.Y + rect.Height - cornerRadius * 2, cornerRadius * 2, cornerRadius * 2, 0, 90);
 roundedRect.AddLine(rect.Right - cornerRadius * 2, rect.Bottom, rect.X + cornerRadius * 2, rect.Bottom);
 roundedRect.AddArc(rect.X, rect.Bottom - cornerRadius * 2, cornerRadius * 2, cornerRadius * 2, 90, 90);
 roundedRect.AddLine(rect.X, rect.Bottom - cornerRadius * 2, rect.X, rect.Y + cornerRadius * 2);
 roundedRect.CloseFigure();
 return roundedRect;
}