asp.net GDI+把图片绘制成自定义的椭圆形状

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using System.Web.UI;
 using System.Web.UI.WebControls;
 using System.Drawing;
 using System.Drawing.Drawing2D;

 public partial class _Default : System.Web.UI.Page
 {
     protected void Page_Load(object sender, EventArgs e)
     {
         Bitmap bitmap = new Bitmap(, );
         Graphics g = Graphics.FromImage(bitmap);
         g.Clear(Color.White);
         TextureBrush mytextbrush = new TextureBrush(System.Drawing.Image.FromFile(Server.MapPath("~/images/001aa.jpg")));
         g.FillEllipse(mytextbrush,,,,);
         System.IO.MemoryStream ms=new System.IO.MemoryStream();
         bitmap.Save(ms,System.Drawing.Imaging.ImageFormat.Jpeg);
         Response.ClearContent();
         Response.ContentType = "image/Jpeg";
         Response.BinaryWrite(ms.ToArray());
     }
 }