初涉 GDI+

照着资料改的一个画图方法中间出现了一大块黑色区域  没搞明白为啥      //自己写的一个画图方法
        public void DrawCurve(Page page, DataSet ds, int sum)
        {
            #region  图片的设置            //获取记录数量
            int count = ds.Tables[0].Rows.Count;
            int wd = 80 + 20 * (count - 1);
            if (wd < 800)
                //{ 
                wd = 800;// }            Bitmap img = new Bitmap(wd, 800);
            Graphics g = Graphics.FromImage(img);
            Pen Bp = new Pen(Color.Black);
            Pen Rp = new Pen(Color.Red);
            Pen Sp = new Pen(Color.Silver);
            Font BigTitleFont = new Font("Arial", 12, FontStyle.Bold);
            Font NomalFont = new Font("Arial", 6);
            Font BigFont = new Font("Arial", 9);
            #endregion
            g.DrawRectangle(new Pen(Color.White, 400), 0, 0, img.Width, img.Height);
            //画标题的brush
            LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, img.Width, img.Height), Color.Black, Color.Black, 1.2F, true);
            LinearGradientBrush Bluebrush = new LinearGradientBrush(new Rectangle(0, 0, img.Width, img.Height), Color.Blue, Color.Blue, 1.2F, true);
            //绘制大标题
            string bigtitle = "历史记录曲线图";
            g.DrawString(bigtitle, BigTitleFont, brush, 40, 5);
            //取得当前发送量
            double nums = 0;
            for (int i = 0; i < count; i++)
            {
                var value = ds.Tables[0].Rows[i]["recordvalue"].ToString().Split('|');
                if (value.Length == 2)
                {
                    nums += Convert.ToDouble(value[1].ToString());
                    break;
                }
                if (value.Length == 1)
                {
                    nums += Convert.ToDouble(value[0].ToString());
                    break;
                }
                if (value.Length == 3)
                {
                    nums += Convert.ToDouble(value[2].ToString());
                    break;
                }
            }
            //绘制信息简报
            string info = "这是信息简报";//"记录时间：" + ds.Tables[0].Rows[0]["recordtime"].ToString() + "  曲线图生成时间：" + DateTime.Now.ToString() + "  记录总量：" + sum.ToString() + "  当前发送总量：" + nums.ToString();
            g.DrawString(info, BigFont, Bluebrush, 40, 25);
            //绘制图片边框
            g.DrawRectangle(Bp, 0, 0, img.Width - 1, img.Height - 1);            //绘制竖坐标线       
            for (int i = 0; i < count; i++)
            {
                g.DrawLine(Sp, 40 + 20 * i, 60, 40 + 20 * i, 720);
            }
            //绘制时间轴坐标标签
            for (int a = 0; a < ds.Tables[0].Rows.Count;a++)
            {                string st = Convert.ToDateTime(ds.Tables[0].Rows[a][1]).ToShortTimeString();
                g.DrawString(st.ToString(), NomalFont, brush, 30 + 20 * a, 370);
            }
            //绘制横坐标线
            for (int i = 0; i < 21; i++)
            {
                g.DrawLine(Sp, 40, 60 + 30 * i, 40 + 20 * (count - 1), 60 + 30 * i);
                int s = 100 - i * 10;
               
                 
                //绘制发送量轴坐标标签
                g.DrawString(s.ToString(), NomalFont, brush, 10, 60 + 30 * i);
            }            //绘制竖坐标轴
            g.DrawLine(Bp, 40, 55, 40, 360);
            //绘制横坐标轴
            g.DrawLine(Bp, 40, 360, 45 + 20 * (count - 1), 360);            //定义曲线转折点
            Point[] p = new Point[count];
            for (int i = 0; i < count; i++)
            {
                var value = ds.Tables[0].Rows[i]["recordvalue"].ToString().Split('|');
                string thevalue = "";
                if (value.Length == 2)
                {
                    thevalue = value[1].ToString();                }
                if (value.Length == 1)
                {
                    thevalue = value[0].ToString();                }
                if (value.Length == 3)
                {
                    thevalue = value[2].ToString();                }
                p[i].X = 40 + 20 * i;
                thevalue = Math.Round(Convert.ToDouble(thevalue),0).ToString();
                p[i].Y =360 -  Convert.ToInt32(thevalue)*3 ;// 360 - Convert.ToInt32(thevalue) / 5 * 3 / 5;
            }
            //绘制发送曲线
            g.DrawLines(Rp, p);
            
            for (int i = 0; i < count; i++)
            {
                var value = ds.Tables[0].Rows[i]["recordvalue"].ToString().Split('|');
               string thevalue = "";
                if (value.Length == 2)
                {
                  thevalue    = value[1].ToString();
                   
                }
                if (value.Length == 1)
                {
                   thevalue= value[0].ToString();
                    
                }
                if (value.Length == 3)
                {
                    thevalue = value[2].ToString();
                   
                }
                //绘制发送记录点的发送量
                g.DrawString(thevalue, NomalFont, Bluebrush, p[i].X, p[i].Y - 10);
                //绘制发送记录点
                g.DrawRectangle(Rp, p[i].X - 1, p[i].Y - 1, 2, 2);
            }
            //绘制竖坐标标题
            g.DrawString("数值", BigFont, brush, 5, 40);
            //绘制横坐标标题
            g.DrawString("时间", BigFont, brush, 40, 385);            #region 保存绘制的图片,图片输出            MemoryStream stream = new MemoryStream();
            img.Save(stream, ImageFormat.Jpeg);            page.Response.Clear();
            page.Response.ContentType = "image/jpeg";
            page.Response.BinaryWrite(stream.ToArray());
            #endregion
        }GDI+asp.net