1.新建Bitmap，并用Graphics来画图和标注文字，具体代码如下：

        Bitmap image = new Bitmap(width, height);
        Graphics graphics = Graphics.FromImage(image);
        try
        {
            graphics.Clear(Color.White);
            Font font = new Font("Arial", 9, FontStyle.Regular);//坐标刻度所使用的字体
            Font font1 = new Font("宋体", 15, FontStyle.Regular);//图片标题所使用的字体
            Font font2 = new Font("宋体", 10, FontStyle.Regular);//注释信息所使用的字体
            LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Gray, Color.Gray, 1.2f, true);//绘制网格线的LinearGradientBrush
            LinearGradientBrush brush2 = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Red, Color.Red, 1.2f, true);//注释信息的LinearGradientBrush
            LinearGradientBrush brush3 = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Green, Color.Green, 1.2f, true);//注释信息的LinearGradientBrush
            LinearGradientBrush brush4 = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Brown, Color.Brown, 1.2f, true);//注释信息的LinearGradientBrush

            graphics.FillRectangle(Brushes.White, 0, 0, width, height);
            Brush brush1 = new SolidBrush(Color.Black);
            if (manqpfl.Length > 0 & manqpfl1.Length > 0 & manqpfl2.Length > 0)
            {
                graphics.DrawString(" 从" + MinYear.ToString() + "年"+MinMonth.ToString()+"月到" + MaxYear.ToString() + "年"+MaxMonth.ToString()+"月的满期数据折线图", font1, brush1, new PointF(width / 2 - 200, 30));//标注图片标题
                graphics.DrawString("商业险为红色折线", font2, brush2, new PointF(width / 2 + 200, 500));//标注注释信息
                graphics.DrawString("交强险为绿色折线", font2, brush3, new PointF(width / 2 + 200, 530));//标注注释信息
                graphics.DrawString("车  险为棕色折线", font2, brush4, new PointF(width / 2 + 200, 560));//标注注释信息
            }
            //画图片的边框线
            graphics.DrawRectangle(new Pen(Color.Black), 0, 0, image.Width - 1, image.Height - 1);
    
            //绘制Y轴
            int x = 60;
            Pen mypen1 = new Pen(Color.Black, 2);
            graphics.DrawLine(mypen1, x, 120, x, 458);
            //绘制网格纵线
            Pen mypen = new Pen(brush, 1); 
            for (int i = 0; i < TotalMonths; i++)
            {
                graphics.DrawLine(mypen, x, 120, x, 458);
                x = x + 60;  //Y轴上每60像素为一个单位刻度
            }
            //绘制网格横线
            int y = 158;
            for (int i = 0; i < 5; i++)
            {
                graphics.DrawLine(mypen, 60, y, width-15, y);
                y = y + 60;  //X轴上每60像素为一个单位刻度
            }
            //绘制X轴
            graphics.DrawLine(mypen1, 60, y, width-15, y);

            //标注x轴文字
            x = 35;
            for (int i = 0; i < TotalMonths; i++)
            {
                string month= ds.Tables[0].Rows[i]["yy"].ToString() + "." + ds.Tables[0].Rows[i]["mm"].ToString();
                graphics.DrawString(month.ToString(), font, Brushes.Red, x, 460); //设置文字内容及输出位置
                x = x + 60;  //X轴上每60像素为一个单位刻度
            }
            //y轴文字
            String[] m = { " 90", " 80", " 70", " 60", " 50" ," 40"};
            y = 150;
            for (int i = 0; i < 6; i++)
            {
                graphics.DrawString(m[i].ToString(), font, Brushes.Red, 25, y); //设置文字内容及输出位置
                y = y + 60; //Y轴上每60像素为一个单位刻度
            }

            int[] Count = new int[TotalMonths];
            int[] Count1 = new int[TotalMonths];
            int[] Count2 = new int[TotalMonths];
            for (int j = 0; j < TotalMonths; j++)
            {
                Count[j] = Convert.ToInt32(manqpfl[j] * 360 / 60);//求数据点对坐标轴的相对位移
                Count1[j] = Convert.ToInt32(manqpfl1[j] * 360 / 60);
                Count2[j] = Convert.ToInt32(manqpfl2[j] * 360 / 60);
            }

            Point[] myPoint = caculatePoints(Count, TotalMonths);//求出数据点在屏幕上的绝对位置
            Point[] myPoint1 = caculatePoints(Count1, TotalMonths);
            Point[] myPoint2 = caculatePoints(Count2, TotalMonths);

            Pen mypen2 = new Pen(Color.Red, 2);//manqpfl折线为红色
            Pen mypen3 = new Pen(Color.Green, 2);//manqpfl1折线为绿色
            Pen mypen4 = new Pen(Color.Brown, 2);//manqpfl2折线为棕色

            graphics.DrawLines(mypen2, myPoint);  //绘制manqpfl折线
            graphics.DrawLines(mypen3, myPoint1);  //绘制manqpfl1折线
            graphics.DrawLines(mypen4, myPoint2);  //绘制manqpfl2折线
           
            //标注数据点的值
            for (int i = 0; i < TotalMonths;i++ )
            {
                graphics.DrawString(manqpfl[i].ToString(), font, Brushes.Blue, myPoint[i].X-8, myPoint[i].Y);
                graphics.DrawString(manqpfl1[i].ToString(), font, Brushes.Blue, myPoint1[i].X-8, myPoint1[i].Y-15);
                graphics.DrawString(manqpfl2[i].ToString(), font, Brushes.Blue, myPoint2[i].X-8, myPoint2[i].Y-15);
            }

            //输出Bitmap
            System.IO.MemoryStream MStream = new System.IO.MemoryStream();
            image.Save(MStream, System.Drawing.Imaging.ImageFormat.Gif);
            Response.ClearContent();
            Response.ContentType = "image/Gif";
            Response.BinaryWrite(MStream.ToArray());
            //this.mess.InnerHtml = MStream.ToArray().ToString();
        }
        finally
        {
            graphics.Dispose();
            image.Dispose();
        }

    //计算折线中点的坐标
    protected Point[] caculatePoints(int[] Count,int TotalNumber)
    {
        Point[] myPoint = new Point[TotalNumber];
        for (int i = 0; i < TotalNumber; i++)
        {
            myPoint[i].X = 60 + i * 60; myPoint[i].Y = 700 - Count[i];
        }
        return myPoint;
    }

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