asp.net GDI+绘制矩形渐变

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(200, 100);
        Graphics graphics = Graphics.FromImage(bitmap);
        graphics.Clear(Color.White);
        Rectangle rectangle = new Rectangle(0, 0, 200, 100);
        LinearGradientBrush mylineargradientbrush = new LinearGradientBrush(rectangle, Color.White, Color.Green, LinearGradientMode.ForwardDiagonal);
        graphics.FillRectangle(mylineargradientbrush, 0, 0, 200, 100);
        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());
    }
}