Dobbelt Buffering

jeg ved godt jeg har udkommenteret dobbelt buffering i overstående, men det var bare for at teste om det var der fejlen lå

her er koden fra dobbelt buffer klassen
    CMemDC(CDC* pDC, const CRect* pRect = NULL) : CDC()
    {
        ASSERT(pDC != NULL);

        // Some initialization
        m_pDC = pDC;
        m_oldBitmap = NULL;
        m_bMemDC = !pDC->IsPrinting();

        // Get the rectangle to draw
        if (pRect == NULL)
        {
            pDC->GetClipBox(&m_rect);
        }
       
        else
       
        {
            m_rect = *pRect;
        }

        if (m_bMemDC)
        {
            // Create a Memory DC
            CreateCompatibleDC(pDC);

            pDC->LPtoDP(&m_rect);

            SetMapMode(pDC->SetMapMode(MM_ANISOTROPIC));

            SetWindowExt(pDC->SetWindowExt(100, 300));
            SetViewportExt(pDC->SetViewportExt(m_rect.Width(), m_rect.Height()));

           
        pDC->DPtoLP(&m_rect);
           
            SetWindowOrg(m_rect.left, m_rect.top);

            m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
            m_oldBitmap = SelectObject(&m_bitmap);

           
           
   

            ///////////////////////////////////////////////////////////////
//            dc.SetMapMode(MM_ANISOTROPIC);                           
//            dc.SetWindowExt(100, 300);                               
//            dc.SetViewportExt(cRect.Width(), cRect.Height());   

               
        ///////////////////////////////////////////////////////////////
        }
       
        else
        {
            // Make a copy of the relevent parts of the current DC for printing
            m_bPrinting = pDC->m_bPrinting;
            m_hDC      = pDC->m_hDC;
            m_hAttribDC = pDC->m_hAttribDC;
        }

        // Fill background
        FillSolidRect(m_rect, pDC->GetBkColor());
    }
   

    ~CMemDC()   
    {       
        if (m_bMemDC) {
            // Copy the offscreen bitmap onto the screen.
            m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
                            this, m_rect.left, m_rect.top, SRCCOPY);           
           
            //Swap back the original bitmap.
            SelectObject(m_oldBitmap);       
        } else {
            // All we need to do is replace the DC with an illegal value,
            // this keeps us from accidently deleting the handles associated with
            // the CDC that was passed to the constructor.           
            m_hDC = m_hAttribDC = NULL;
        }   
    }
   
    // Allow usage as a pointer   
    CMemDC* operator->()
    {
        return this;
    }   

    // Allow usage as a pointer   
    operator CMemDC*()
    {
        return this;
    }
};

lukker