asp.net GDI+ 使用PathGradienBrush类实现彩色渐变

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(400, 200);
        Graphics graphics = Graphics.FromImage(bitmap);
        graphics.Clear(Color.White);
        Point centerPoint = new Point(100, 100);
        int r = 100;
        GraphicsPath path = new GraphicsPath();
        path.AddEllipse(centerPoint.X - r, centerPoint.Y - r, 2 * r, 2 * r);
        PathGradientBrush mypathgradientBrush = new PathGradientBrush(path);
        mypathgradientBrush.CenterPoint = centerPoint;
        mypathgradientBrush.CenterColor = Color.DarkGreen;
        mypathgradientBrush.SurroundColors = new Color[] { Color.Gold };
        graphics.FillEllipse(mypathgradientBrush, centerPoint.X - r, centerPoint.Y - r, 2 * r, 2 * r);
        centerPoint = new Point(300, 100);
        r = 33;
        path = new GraphicsPath();
        path.AddEllipse(centerPoint.X - r, centerPoint.Y - r, 2 * r, 2 * r);
        path.AddEllipse(centerPoint.X - 2*r, centerPoint.Y - 2*r, 4 * r, 4 * r);
        path.AddEllipse(centerPoint.X - 3 * r, centerPoint.Y - 3 * r, 6 * r, 6 * r);
        mypathgradientBrush = new PathGradientBrush(path);
        mypathgradientBrush.CenterPoint = centerPoint;
        mypathgradientBrush.CenterColor = Color.Gold;
        mypathgradientBrush.SurroundColors = new Color[] { Color.Black, Color.Blue, Color.DarkGreen };
        graphics.FillPath(mypathgradientBrush, path);
        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());
    }
}