如何将Panel里的内容全部旋转90度后打印？

 [System.Runtime.InteropServices.DllImportAttribute( "gdi32.dll ")]
                         private   static   extern   bool   BitBlt(
                                        IntPtr   hdcDest,   //   handle   to   destination   DC
                                        int   nXDest,   //   x-coord   of   destination   upper-left   corner
                                        int   nYDest,   //   y-coord   of   destination   upper-left   corner
                                        int   nWidth,   //   width   of   destination   rectangle
                                        int   nHeight,   //   height   of   destination   rectangle
                                        IntPtr   hdcSrc,   //   handle   to   source   DC
                                        int   nXSrc,   //   x-coordinate   of   source   upper-left   corner
                                        int   nYSrc,   //   y-coordinate   of   source   upper-left   corner
                                        System.Int32   dwRop   //   raster   operation   code
                         );

        Bitmap myImage;
        private void button1_Click(object sender, EventArgs e)
        {
            Graphics g1 = panel1.CreateGraphics();
            myImage = new Bitmap(this.panel1.Width, this.panel1.Height, g1);
            Graphics g2 = Graphics.FromImage(myImage);
            IntPtr dc1 = g1.GetHdc();
            IntPtr dc2 = g2.GetHdc();
            BitBlt(dc2, 0, 0, this.panel1.Width, this.panel1.Height, dc1, 0, 0, 13369376);
            g1.ReleaseHdc(dc1);
            g2.ReleaseHdc(dc2);

            myImage.RotateFlip(RotateFlipType.Rotate90FlipNone);

            PageSetupDialog mypgDialog = new PageSetupDialog();
            mypgDialog.Document = printDocument1;

            try
            {
                mypgDialog.ShowDialog();
            }
            catch
            {
                printDocument1.PrintController.OnEndPrint(printDocument1, new System.Drawing.Printing.PrintEventArgs());
            }
            //*****************************

            PrintPreviewDialog dlg = new PrintPreviewDialog();

            dlg.Document = printDocument1;

            dlg.Document.DefaultPageSettings.PaperSize = new System.Drawing.Printing.PaperSize("cardc", 324, 204);

            if (dlg.ShowDialog() == DialogResult.OK)
            {
                printDocument1.Print();
            }

            g1.Dispose();

        }

     
        private void printDocument1_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
        {
            e.Graphics.DrawImage(myImage, new Point(10, 10));
        }