private void showLineNo()
{
//获得当前坐标信息
Point p = this.richTextBox1.Location;
int crntFirstIndex = this.richTextBox1.GetCharIndexFromPosition(p);
int crntFirstLine = this.richTextBox1.GetLineFromCharIndex(crntFirstIndex);
Point crntFirstPos = this.richTextBox1.GetPositionFromCharIndex(crntFirstIndex);
//
p.Y += this.richTextBox1.Height;
//
     int crntLastIndex = this.richTextBox1.GetCharIndexFromPosition(p);
     int crntLastLine = this.richTextBox1.GetLineFromCharIndex(crntLastIndex);
     Point crntLastPos = this.richTextBox1.GetPositionFromCharIndex(crntLastIndex);
     //
     //
     //准备画图
     Graphics g = this.panel1.CreateGraphics();
     Font font = new Font(this.richTextBox1.Font,this.richTextBox1.Font.Style);
     SolidBrush brush = new SolidBrush(Color.Green);
     //
     //
     //画图开始
     //刷新画布
     Rectangle rect = this.panel1.ClientRectangle;
     brush.Color = this.panel1.BackColor;
g.FillRectangle(brush, 0, 0, this.panel1.ClientRectangle.Width,this.panel1.ClientRectangle.Height);
     brush.Color = Color.Green;//重置画笔颜色
     //
     //绘制行号
     int lineSpace = 0;
     if (crntFirstLine != crntLastLine)
     {
          lineSpace = (crntLastPos.Y - crntFirstPos.Y) / (crntLastLine - crntFirstLine);
     }
     else
     {
          lineSpace = Convert.ToInt32(this.richTextBox1.Font.Size);
     }
     int brushX = this.panel1.ClientRectangle.Width - Convert.ToInt32(font.Size * 3);
     int brushY = crntLastPos.Y+ Convert.ToInt32(font.Size*0.21f);//惊人的算法啊！！
     for (int i = crntLastLine; i >= crntFirstLine;i-- )
     {
           g.DrawString((i + 1).ToString(), font, brush, brushX, brushY);
           brushY -= lineSpace;
     }
     g.Dispose();
     font.Dispose();
     brush.Dispose();
}