RichTextBox EM_FORMATRANGE RotateTransform cloudly output

Question

Hello,

i have the problem that the output of my Program is in one case total cloudly.

So i use a RichTextBox and the EM_FORMATRANGE Message to render the output to Metafile.

IntPtr hdc = _g.GetHdc();

Metafile metafile = new Metafile(hdc, new RectangleF(0, 0, iWidth, iHeight), MetafileFrameUnit.Pixel); 

Graphics g1 = Graphics.FromImage(metafile); 

IntPtr hDCEMF = g1.GetHdc();

fRange.chrg.cpMin = 0;

fRange.chrg.cpMax = -1;

fRange.hdc = hDCEMF;

fRange.hdcTarget = hDCEMF;

fRange.rcPage = LayoutAreaPage;

fRange.rc = LayoutArea;

IntPtr wparam = IntPtr.Zero;

wparam = new IntPtr(1);

IntPtr lparam = IntPtr.Zero;

lparam = Marshal.AllocCoTaskMem(Marshal.SizeOf(fRange));

Marshal.StructureToPtr(fRange, lparam, false);

SendMessage(m_RichTextCtrl.Handle, EM_FORMATRANGE, wparam, lparam);

Marshal.FreeCoTaskMem(lparam);

SendMessage(m_RichTextCtrl.Handle, EM_FORMATRANGE, (IntPtr)0, (IntPtr)0);

_g.ReleaseHdc();

g1.ReleaseHdc();

g1.Dispose();


_g.TranslateTransform(iLeft, iTop);

_g.RotateTransform((float)m_Rotation); 

_g.DrawImage(metafile, 0, 0, iWidth, iHeight);

 

Scenario 1:

When i use a default RichtextBox, everthing is OK.

 

Scenario 2:

When i use a override RichTextBox with transparent background.

 class RichTextCtrl : RichTextBox
    {
        public const int WS_EX_TRANSPARENT = 0x20;


        public RichTextCtrl()
        {
            this.SetStyle(ControlStyles.Opaque, true);            
            this.SetStyle(ControlStyles.SupportsTransparentBackColor, true);
        }

        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams createParams = base.CreateParams;
                // Transparent background
                createParams.ExStyle |= WS_EX_TRANSPARENT;
                Visible = false;

                return createParams;
            }
        }
    }

Everthing is Ok, except rotate 180 degree.

I meen only exact 180 degree. 179.95 or 180.05 are working fine.

 

For me it seems like a problem in the .net framework.

Thanks for every help in advanced,

Thorsten.