[SOLVED] C++: Avoid flickering using WM_ERASEBKGND-Message in MFC-Application

C++: Avoid flickering using WM_ERASEBKGND-Message in MFC-Application

in the OnDraw()-Method i create a Bitmap and blit it to the output every time the window size changes:

void CmbmView::OnDraw(CDC* pDC)
{
  CRect WindowSize;
  HDC hdc;
  BITMAPINFO pbmi;
  HBITMAP hbm;
  CBitmap *pBitmap;
  CDC MemDC;
  void* ppvBits;

  GetClientRect(WindowSize);

  hdc = CreateDC (TEXT ("DISPLAY"), NULL, NULL, NULL) ;

  memset(&pbmi, 0, sizeof(BITMAPINFO));
  pbmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
  pbmi.bmiHeader.biWidth = WindowSize.Width();
  pbmi.bmiHeader.biHeight = -WindowSize.Height(); // top down
  pbmi.bmiHeader.biPlanes = 1;
  pbmi.bmiHeader.biBitCount = 32;
  pbmi.bmiHeader.biCompression = BI_RGB;

  hbm = CreateDIBSection(hdc, &pbmi, DIB_RGB_COLORS, &ppvBits, NULL, NULL);
  pBitmap = CBitmap::FromHandle(hbm);

  MemDC.CreateCompatibleDC(pDC); 
  MemDC.SelectObject(pBitmap);

  // "Draw" into ppvBits
  GetDocument()->DrawApple(pDC, ppvBits, WindowSize.Width(), WindowSize.Height(), m_MaxIter, m_MaxBetragQuadrat, m_BW);

  // Blit it to the output
  pDC->BitBlt(0, 0, WindowSize.Width(), WindowSize.Height(), &MemDC, 0, 0, SRCCOPY);
}

But every time the application needs to recreate the bitmap in OnDraw(), the Screen gets white until it blits the bitmap to the screen. How can i use the WM_ERASEBKGND-Message to avoid this flickering?

Solution

I don't know with MFC but with the native Windows API you have to process the WM_ERASEBKGND message and simply return TRUE;. This tells the default window procedure that the message is processed hence the window background is erased. As a result the flickering disappears.

Additionally if you're using function InvalidateRect(..) be sure to set parameter bErase to FALSE. Note that the parameter is TRUE by default if not explicitly given.